MAGNETIC EFFECT OF CURRENT · An electromagnet shows magnetic properties only as long as the...

MAGNETIC EFFECT OF CURRENT 1. Lodestone. The black ore of iron (Fe304) called magnetite, capable of attracting similar pieces

of iron is called Lodestone. They are naturally existing magnets used by man to find the

directions. Now-a-days we use magnetic needles to find direction. The end pointing towards

the geographic North is called North pole and the South seeking pole is called South pole.

2. Basic Laws of Magnetism.

3. (1) There are two poles namely North pole and South pole.

4. (ii) Like poles repel each other, while unlike poles attract each other.

5. Oersted's Experiment. H. C. Oersted, a Danish physicist first noticed the magnetic effect of

electric current. According to him, a needle kept near the wire carrying current will deflect

due to the magnetic field produced. Any change in direction of current will show variation in

deflection.

6. Magnets. The smallest magnetic element that can be built is called a magnet. It has two poles

named North and South pole. When it is hung using a string tied to its middle, the two poles

will seek North and South of earth. When broken, a magnet becomes two magnets. Magnetic

monopoles do not exist.

7. Magnetic Substances. Those substances which are attracted by a magnet are called magnetic

substances. Examples : iron, nickel, cobalt, steel

8. Non-magnetic Substances. Those substances which are not attracted by a magnet are called

non-magnetic substances.

9. Examples : wood, glass, copper, aluminium, brass, paper, etc.

10. Magnetic Field. Surrounding a magnet its influence is felt by any other magnetic element. It

may be an attractive or a repulsive influence. The strength is defined as the force experienced

by unit magnetic North pole placed at a point. It is measured in Tesla or Weber/m2.

11. Magnetic field is a quantity that has both magnitude and direction. The direction of the

magnetic field is taken to be the direction in which a north pole of the compass needle moves

inside it.

12. Magnetic Field Lines. When a bar magnet is placed on a cardboard and iron-filings are

sprinkled, they will arrange themselves in a pattern as shown below.

13. They are said to align along the field lines of the bar magnet.

14. To picturise magnetic field lines, follow the following steps :

a) Bring the needle close to North pole and mark the tips of the needle.

b) Move the compass such that, one end points the fixed farther point and place a point on the

other end of the needle.

c) Repeat the steps till the South pole is reached.

d) Join all these points to get a line and put an arrow to indicate direction.

e) Repeat the four steps to show many lines, which will resemble the orientations of iron filings.

15. Properties of magnetic field lines

a) The magnetic field lines never intersect each other because if they do so it means that at that

point the compass needle would point towards two directions which is not possible.

OR The field lines emerge from the north pole and merge at the south pole side of magnet

.Inside the magnet, the direction of field lines is from its south pole to its north pole. Thus the

magnetic field lines are closed curves. This is why no two field-lines are found to cross each

other.

b) They emerge at North Pole and merge at South Pole (closed loops are formed).

c) They are crowded near the poles and are far apart near the middle.

d) These are directed from North Pole to South Pole outside the magnet and from south to North

Pole inside the magnet.

e) The strength of magnetic field is indicated by the closeness of the field lines. Closer the lines,

more will be the strength and farther the lines, lesser will be the field strength.

f)

16. Compass needle A compass needle is a small bar magnet whose ends always point towards

north south direction. The end pointing towards north is called North Pole and the end

pointing towards south is called South Pole.

17. Why does a compass needle get deflected when brought near magnet?Compass needle get

deflected when brought near magnet due to the force of the magnet.

18. why iron fillings align themselveswhem it bis brought near magnet ?

19. The iron fillings align themselves to represent magnetic lines of force.

20. Magnet in a Magnetic Field. When a magnet is placed in a magnetic field, it aligns along the

field lines with the north pole on the direction of the magnetic field. In the same manner,

magnetic needle also aligns. On the surface of earth there exists a magnetic field due to the

contents of the earth making it to behave as a magnet. This is the reason why magnetic needle

is being used to find direction on the surface of earth.

21. Magnetic Field around a Current Carrying Straight Conductor. Insert a wire carrying

current through a hole at the middle of a cardboard. When a current I is passed through the

wire, surrounding the wire, magnetic field will be created. When you sprinkle iron filings, on

the board, they will all settle in concentric rings. The direction of North pole is given by the

arrow. Reversal of current will reverse the magnetic field.

22. The direction of magnetic field produced by the electric current depends upon the

direction of flow of current .

a. If we reverse the direction of current then the direction of magnetic field produced by the

electric current get changed.

b. The magnitude of the magnetic field produced at a given point increases as the current

through the wire increases.

c. The concentric circles representing the magnetic field around a current-carrying straight

wire become larger and larger as we move away from it. ( or we can say it directly

depends on current and in inversely on radius )

23. Right Hand Thumb Rule. Hold the wire carrying current in your right hand, such that the

thumb indicates the direction of current, then the folded fingers will indicate the presence of

magnetic field (lines) surrounding the wire.

24. Magnetic Field due to a Current Carrying Circular Wire. The field created due to a

circular coil is given by the figure. The direction of field is perpendicular to the plane of the

coil and directed inwards for the clockwise current flowing. For anticlockwise current, it will

be flowing anticlockwise.

25. The field lines in circular coil have the following characters :

a. Circular near the wire.

b. Straight at the centre.

c. Field is perpendicular to the plane of the coil.

d. For larger areas, the field at the centre is uniform.

e. Field lines will enter into one plane and leave the other. (Enter on the side with clockwise

current).

26. Gfhdg

27. The magnetic field at the centre of the circular coil due to a current is dependent

a. directly on the current,

b. directly on the number of turns and

c. inversely on the radius of the coil.

28. The direction of current can determine which pole it will behave like

MAGNETIC FIELD PRODUCED BY A CURRENT-CARRYING SOLENOID

29. SOLENOID :Long cylindrical coil consisting of a large number of turns of an insulated wire

is called a solenoid. An iron rod is usually placed inside the hollow tube. This iron rod is

called the core. When current is passed through a solenoid, a magnetic field gets developed

around it.

A. The electric current in each circular loop of a solenoid flows in the same direction.

B. The magnetic fields of all the loops add up to make solenoid act as a bar magnet for any point

outside it.

C. One end of the current-carrying solenoid acts as the north pole, while the other end as the

south pole.

D. The end of a solenoid at which current flows in an anticlockwise direction acts as a north

pole, while the end at which current flows in a clockwise direction acts as a south pole. This

rule is called clock rule

30.

31. On what factors does the strength of the magnetic field produced by a current-carrying solenoid

depend Strength of the magnetic field produced by a current-carrying solenoid depends upon the

following factors:

A. The strength of the magnetic field (B) produced by a current-carrying solenoid is directly proportional

to the number ol turns in the coil.

B. The larger the number of turns in the solenoid, stronger is the magnetic field produced.

C. The strength of the magnetic field (B) produced by a current-carrying solenoid is directly proportional

to the current (I) flowing through the solenoid.

D. The higher is the current, stronger is the magnetic field produced.

E. The nature of the core material ,the magnetic field produced when soft iron is used as the core material

is very strong. Thus, the core of a solenoid acts as an electromagnet.

32. Magnetising a Material. When a material is placed inside a coil carrying current (may be a

solenoid), it will get magnetised. A bunch of nails or an iron rod placed along the axis of the

coil can be magnetised by the current allowed to pass through the coil. Once the current is

put- off the magnetic field will also be lost. Such magnets are called electro-magnets.

33. Permanent Magnets are made of carbon steel, chromium steel, tungsten steel and some alloys

like Alnico and Nipermag. If the rod which is magnetised using a solenoid is made of steel

then the magnetism acquired will not be lost even after the removal of current. Such magnets

are called permanent magnets.

34. What is an electromagnet : Electromagnets are based on the magnetic effect of electric

current. An electromagnet is usually prepared by placing a soft iron core in a solenoid, or by

winding a large number of turns of an insulated wire (generally the insulated copper wire) on

a cylindrical soft iron core. An electromagnet shows magnetic properties only as long as the

electric current flows through the solenoid. Thus, electromagnets are temporary magnets.

35. Soft iron is used for making the core of an electromagnet because it can be magnetised and

demagnetised easily.

36. Steel can be magnetised only when placed in a very strong magnetic field. When the current is

switched off, steel does not lose its magnetism completely and it becomes a permanent

magnet. It is because of this reason that steel is not used for making the core of an

electromagnet.

37. Uses of Electromagnet.

38. Electromagnets are used in electric bells, loudspeakers, electric motors, telephone diaphragms,

electric fan and for sorting scrap metal and for extraction in hospitals, etc.

39. Giant electromagnets are used in cranes to lift machinery, in shipyards for loading and

unloading purposes and bulk quantity of iron and steel.

40. For lifting heavy loads. Electromagnets are used on cranes to lift heavy loads in steel works

and scrapyards.

41. In hospitals. Electromagnets are used for removing splinters of iron or steel from the injured

eyes.

42. Magnets in Living Beings. When weak current is flowing in nerve cells it causes a temporary

magnetic field (1 billionth of earth's field). Using this magnetic field caused images of body

parts can be taken. This technique is called Magnetic Resonance Imaging (MRI).

Even abdomen of honey bees, bacteria, algae etc., have magnetic elements inside their body

parts.

43. Force on Current Carrying Conductor in Magnetic Field. Ampere suggested that any

current carrying conductor when placed in a magnetic field will experience a force. When a

current I passes through a conductor of length . I placed in a perpendicular magnetic field B,

then the force experienced

44. Fleming's Left Hand Rule. Stretch the first three fingers of the left hand mutually

perpendicular to each other such that the fore finger points the direction of magnetic field, the

middle finger points the direction of current, then the thumb will indicate the direction of

force experienced by the conductor. It is to be applied when the current and field are

perpendicular to each other.

45. Force on a Charge. Similar to a conductor carrying current, a charge moving in a magnetic

field will always experience force in perpendicular direction.

46. Electric Motor. The device used to convert electrical energy to mechanical energy is called

Electric Motor. It is used in fans, machines, etc. Principle. Electric motor works on the

principle of force experienced by a current carrying conductor in a magnetic field. The two

forces in the opposite sides are equal and opposite. Since they act in different lines they

bring rotational motion.

47. Uses of Electric Motor. Electric motor is used as an important component in washing

machines, mixers and blenders, electric fans, refrigerators, hair dryers, generators, water

pumps, record player, tape recorders etc.

48. Electromagnetic Induction. According to Faraday, when a magnet is in motion relative to a

coil attached with a galvanometer, induced electric current is set up in the coil. This idea of

creation of current by changing magnetic strength is called Electromagnetic Induction.

➢ When North pole of a magnet is taken towards a coil with galvanometer, induced

current will flow in such a way that the North pole is created on the side of the magnet

to oppose the change that produces the current.

➢ When North pole is taken towards or South pole is taken towards, the galvanometer

deflection will be opposite. Faster the magnet is moved towards or away from the

galvanometer; the deflection in the galvanometer will be more in opposite directions.

➢ The movement of bar magnet is stopped the deflection of galvanometer is zero or no

deflection.

49. Magnetic Flux. It is defined as the product of the magnetic field and the area through which

magnetic field passes perpendicularly.

50. Faraday's Law. The rate at whifch the magnetic flux linked with a coil changes, produces the

induced emf or current. More the rate, more the current and vice-versa.

51. Fleming's Right Hand Rule. Stretch the first three fingers of the right hand mutually

perpendicular to each other such that the fore finger gives the direction of magnetic field and

the thumb points the direction of the motion of a conductor then, the middle finger will give

the direction of the induced current.

52. Electric Generators. Generator works on the principle of Electromagnetic Induction. It

converts the mechanical energy available into electrical energy. When a coil is rotated in a

magnetic field, then there will be induced current flowing in it. The direction of the induced

current can be found using the Fleming's right hand rule.

53. In India AC generated and used reverses in 1/100 second or has a frequency of 50 Hz.

Alternating current is used for transmission since,

A. Loss of energy is less over large distance.

B. Conversion for necessary potential is possible in AC transformers.

54. D.C current

55. Electric Supply in House. Electrical supply to the house is supplied at 220 volts using two

wires - one using red insulation cover for live wire and the other having black insulation

called neutral wire.

56. Kilowatt Hour. Kilowatt hour is the commercial unit for electrical energy. In houses a

kilowatt hour meter is used for measuring the energy consumed. All electrical appliances are

connected with the earth wire, so that any wrong connection will inactivate the device and

save the device from destruction.

57. Advantages of Alternating Current:

58. Electric power can be transmitted over long distances without much loss of energy.

Therefore the cost of transmission is low. This is made possible with the help of transformer.

Transformer cannot be used for direct current.

59. Alternating current can be controlled by a choke oil, whereas direct current can be controlled

by an ohm resistance and heavy energy losses are in the form of heat.

60. Whenever direct current is required, alternating current can be easily converted into direct

current with the help of rectifiers.

61. Alternating current equipments such as electric motors are more durable and convenient as

compared to D.C. equipments.

62. Disadvantages of Alternating Current:Number of thin wires are twisted to form a thick wire

since at high frequencies the alternating current flows in the outer surface of the conductor.

63. If accidently touched the A.C. wire, it gives a serious jolt or shock as compared to direct

current so A.C. is more dangerous as compared to D.C.

64. House-hold Connection. We use parallel Connection in the various electrical points in the

house. This is because,

65. (z) individual appliance can be operated at any time,

66. (ii) all appliances will get the same potential difference of 220 volts, needed for their

operation.

67. Domestic Electric Circuits. The electric power in our homes is supplied at 220 V, 50 Hz. The

main component of domestic electric circuits are :

68. (z) Live or positive wire - covered with red insulation.

69. Neutral or negative wire - covered with black insulation.

70. Earth wire - covered with green insulation. Live wire is at a high potential of 220 volt whereas

the neutral wire is at zero potential called ground potential. Thus the potential difference

between these two wires is 220 volt.

71. Earthing or Earth Wire. The earth wire is usually connected to a copper plate deep in the earth

near the house. The metallic body of all the electrical appliances is connected to earth wire.

The earth wire provides a low resistance to the current hence any leakage of current to the

metallic body keep its potential equal to that of the earth, i.e., zero potential and the user may

not get a severe electric shock. Earth wire is connected in parallel with domestic circuits.

72. Short Circuit. When the circuit offers zero or negligible resistance to the flow of current, the

circuit is said to be short circuit.

73. It happens when live wire and neutral wire touches each other due to (z) fault in the

appliances (ii) damage in the insulation of two wires. Then according to ohm's law, large

amount of current flows through the circuit because of low resistance. According to Joule's

law of heating effect, heat is produced in the live wire (H oc i2) and produces spark damaging

the devices and wiring at the place of short circuit.

74. Overloading. If the total current drawn by all the appliances at a particular time exceeds the

bearing capacity of that wire, the wires of the domestic wiring get heated. This is known as

overloading.

75. It might be . due to accidental rise in supply voltage connecting many devices to one socket.

76. Fuse Wire. It is a safety wire connected in series in the live wire. In case of any large current

supply or malfunctioning in the electric connections, Joules heating effect takes place, the fuse

wire burns and disconnects the entire circuit from the electrical supply. The fuse wire should

have, (0 low resistance and (ii) low melting point. Normally, the fuse wire is made of an alloy

of copper and tin.

77. Advantage of fuse wire : It protects the circuit and appliances by stopping the flow of any

large electric current - may even be caused by overloading.

78. Transformers are devices which work on the principle of electromagnetic induction. It has two

coils namely, primary and secondary. It is used to step-up or step-down potential. Since power

supplied is to be conserved, the power in primary and secondary should be the same. So when

potential is increased, current will be decreased and vice-versa. A transformer will not work in

DC

79. ACTIVITY1 : Aim : To study the magnetic effect of current flowing through a straight

conductor.

Observation :

➢ As the current passes through the wire, the needle gets deflected.

➢ If the current flows from north to south, the north pole of needle gets

➢ deflected towards east.

➢ On reversing the current in the wire, i.e., from south to north, north pole of needle would

move in west direction.

➢ If we increase the current through the wire, needle will deflect more.

➢ If we move the compass away from the wire, the deflection in the needle will start decreasing.

➢ Increase the distance of the compass needle from the wire and compare the angle with

previous one through which the needle turn.

Conclusion :

➢ Current carrying conductor has a magnetic field associated with it. Direction of magnetic

needle/field at a given point depends on the direction of current v flows in the wire.

➢ Magnitude of the field produced at a given point is directly proportional to the current passing

through the wire.

➢ Magnetic field produced by a given current decreases as the distance from the wire increases.

80. ACTIVITY 2: Aim : To study the magnetic field due to a magnet.

81. Observation :

82. Iron filings are concentrated at the edges.

83. The filings form curves in orderly way.

84. Conclusion :

85. Strength of magnetic field is concentrated at the edge - identified as pole.

86. Field lines are observable with the filings arrangement.

87. Iron filings experience force in the field of the magnet.

88. ACTIVITY3: Aim : To draw magnetic field lines due to a bar magnet.

89. Conclusion :

90. Surrounding a magnet, magnetic field lines of its influence exist.

91. Lines are diverging from poles or converging to poles.

92. Magnetic field lines form closed paths.

93. Close to the magnet, its influence on the needle is more than earth's field.

94. ACTIVITY4 : Aim : To study the magnetic field due to a straight conductor carrying current.

95. Conclusion :

96. Current carrying conductor is a source of magnetic field.

97. Direction of current will determine the direction of magnetic field - reversal of current

reverses magnetic field.

98. Magnetic field B produced depends on the distance r of the needle from the wire. Variation of.

magnitude of current causes change in the strength of the field. B can be found to increase

with increase in the current.

99. ACTIVITY 5 Aim : To study the magnetic field due to a circular coil carrying current.

Conclusion : Magnetic field orientation depends on the current direction. B depends on the

radius of the circular coil.

100. ACTIVITY6 Aim : To study the relationship among the direction of the current, the

field and the motion of the conductor.

➢ Conclusion : 1. The displacement of the rod is caused by the force exerted by the magnet on

the current carrying rod.

➢ 2. The direction of force exerted by the magnet on the rod reverses, when the poles

interchange. Thus, the force exerted by the magnet, current and motion of conductor are

perpendicular to each other which can be illustrated through Fleming's left hand rule.

101. ACTIVITY7 Aim : To study the effect of movement of a conductor and a magnet

relative to each other. Current in the coil is produced due to the relative motion between the

coil and magnet. Current caused does not depend on the fact, whether magnet is moving or

coil is moving. Quicker the movement, the deflection is more - confirming larger emf (i.e.)

current produced is time dependent on the change

102. ACTIVITY8: what happened when magnet is moved inside and outside the solenoid?

103. When the north pole is moved away from the end B of the coil. Galvanometer show

deflection

104. When the north pole is moved towards the end B of the coil. Galvanometer show

deflection in opposite side then the privous.

105. When the south pole is moved towards the end B of the coil. Galvanometer show

deflection

106. When the north pole is moved towards the end B of the coil. Galvanometer show

deflection in opposite side then the privous.

107.

108.

109. ACTIVITY

110. ACTIVITY

111. ACTIVITY

112. ACTIVITY

113. ACTIVITY

114. ACTIVITY

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128. Dsh

129. G

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149.

150.

Magnetic field due to current carrying circular loop:

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We know that the magnetic field produced by a current- carrying straight wire depends inversely on

the distance.

We know that the magnetic field produced by a current- carrying conductor at a given point, depends

directly on the current passing through it.

Therefore, if there is a circular coil having n turns, the field produced is n times as large as produced

by a single turn. This is because the current in each circular turn has the same direction, and the field

due to each turn then just adds up.

Magnetic field due to a current carrying straight wire The straight current carrying conductor

produces a magnetic field around it in the form of concentric circular field lines with the conductor at

the centre.

Factors affecting strength of magnetic field around a current carrying straight conductor. Strength of

magnetic field is directly proportional to the current passing through the conductor and inversely

proportional to the distance from the conductor. ( B a I and B a 1/r )

Right hand thumb rule or Maxwell’s clockwise rule If we hold a straight wire in our right hand, and

if the thumb represents the direction of current then the fingers represent the direction of magnetic

field lines.

Magnetic field due to current carrying circular loop or coil When the current is passed through

circular loop or coil, the lines of force are circular near the wire but straight and parallel near the

centre of loop or coil. Factors affecting magnetic field due to current carrying circular loop or coil.

Magnetic field due to current carrying circular loop at its centre is–

Directly proportional to the current passing through it.

Inversely proportional to the radius of loop.

Magnetic field due to current in a solenoid The Magnetic field due to current carrying solenoid is

similar to the magnetic field produced by a bar magnet. The ends of the solenoid act as North Pole

and South Pole. The field lines inside the solenoid are in the form of straight parallel lines.

Factors affecting Magnetic field due to current in a solenoid

1. Magnetic field is directly proportional to the number of turns in the coil.

2. It is directly proportional to the current passing through it.

3. It is inversely proportional to the length of air gaps between the poles.

4. It depends on the nature of the core material used in the solenoid. Electromagnet.

An electromagnet consists of a long coil of insulated copper wire wrapped around a soft iron core. It

is a temporary magnet as it works as long as current is passed through it. Factors affecting the

strength of magnetic field of an electromagnet

The strength of magnetic field of an electromagnet is –

1. Directly proportional to the number of turns.

2. Directly proportional to the current flowing through it.

3. Inversely proportional to the length of air gaps between the poles.

Uses of electromagnet

1. They are used in electrical devices such as electric bell, electric fan, motor, and generator.

2. They are used for lifting and transporting large mass of iron.

3. They are used in medical practices for removing pieces of iron from wound and used in MRI.

Permanent magnets

A permanent magnet is made from steel alloys like carbon steel, chromium steel, cobalt steel, etc.

They are weaker than electromagnets and their strength and polarity cannot be changed. Force on a

current carrying conductor in a magnetic field.

A current carrying conductor placed in a magnetic field experiences a force due to the interaction

between ---

a. Magnetic field due to current carrying conductor and

b. External magnetic field in which conductor is placed.

Force on a current carrying conductor in a magnetic field

A current carrying conductor placed in a magnetic field experiences a force due to the interaction

between

a. Magnetic field due to current carrying conductor and

b. External magnetic field in which conductor is placed.

Flemming’s Left Hand Rule

If we stretch our thumb, fore finger and the middle finger of our left hand mutually perpendicular and

if the fore finger represents the direction of magnetic field and the middle finger represents the

direction of current then the thumb represents the direction of motion in conductor.

Electric motor

A motor is the device which converts electrical energy into mechanical energy. It has a shaft which

rotates continuously when current is passed through it. It is used in electric fans, mixer grinder, etc.

Principle of electric motor

When a rectangular coil of copper wire is placed in a magnetic field and current is passed through it, a

force acts on the coil which rotates it continuously. Electromagnetic induction. The production of

electric current by moving a straight conductor in a magnetic field is called electromagnetic

induction. It is the production of electricity from magnetism.

Flemming’s Right Hand Rule.

If we stretch our thumb, fore finger and the middle finger of our right hand mutually perpendicular

and if the fore finger represents the direction of magnetic field and the thumb represents the direction

of motion in conductor then the middle finger represents the direction of induced current in the

conductor.

Electric generator

A generator is a machine which is used to generate electric current by converting mechanical energy

into electrical energy. There are two types of generators – alternating current (AC) generator and

direct current (DC) generator.

Principle of electric generator When a coil of copper wire is moved in a strong magnetic field, a

current is induced in the coil.

Earthing

The appliances that have metallic body (like electric iron, toaster, refrigerator, etc.) are connected

with green wire which provides a low resistance conducting path for the current and keeps the body

of appliance at the potential of the earth. This is called earthing.

Earthing is done to save ourselves from electric shocks.

Electric fuse

The device having a short length of thin wire which is made of alloy lead and tin is called fuse wire or

electric fuse. It has a very low melting point. It melts and breaks the circuit if the current exceeds the

safe value.

Fuse wire is connected in series in the circuit.

Overloading

When too many electrical appliances of high power rating (electric oven, air conditioner, etc.) are

switched on at the same time, a large current from the circuit is drawn. This is called overloading of

the circuit. It may also occur when the live wire and the neutral wire come into direct contact.

Steps to avoid overloading

Short circuiting When the live wire and neutral wire come into direct contact, a large amount of

current flows through the circuit due to very small resistance, this is called short circuiting. The heat

produced during short circuiting is so high that it may cause fire.

NCERT Magnetic Effects of Currents SOLVED QUESTIONS

3 marks Qns & ans of Magnetic Effects of Currents

1. Why does a current carrying conductor kept in a magnetic field experience force? On what factors

does the direction of this force depend? Name and state the rule used for determination of direction of

this force.

Answer: Force on a conductor carrying current in a magnetic field :-

A.M. Ampere suggested that if a current carrying conductor produces a magnetic field and exerts a

force on a magnet, then a magnet should also exerts a force on a current carrying conductor.

Eg :- If an aluminum rod is suspended horizontally by a wire between the poles of a horse shoe

magnet and current is passed through the wire, then the aluminum rod is displaced. If the direction of

current is reversed, the direction of displacement is also reversed. The force exerted is maximum if

the conductor is perpendicular to the magnetic field.

Fleming’s Left Hand Rule :-

The direction of force (motion) of a current carrying conductor in a magnetic field is given by

Fleming’s Left Hand Rule.

It states that ‘ If we hold the thumb, fore finger and middle finger of the left hand perpendicular to

each other such that the fore finger points in the direction of magnetic field, the middle finger points

in the direction of current, then the thumb shows the direction of force (motion) of the conductor

2. Explain a) Electric fuse b) Overloading c) Short circuit

Answer: a) Electric fuse :-

Electric fuse is a safety device used in electric circuits to protect the circuit and appliances from

damage due to overloading and short circuit. It is a wire having high resistance and low melting point.

If excess current flows through the circuit, the fuse wire melts and breaks the circuit. Fuse wire is

made of a metal or an alloy of metals like lead, tin, aluminium and copper. Fuse wire is connected in

series with the live wire.

b) Overloading :-

Overloading is caused due to increase in voltage, or if the live wire and neutral wire comes in contact

or if too many appliances are connected to a single socket. It results in overheating of the wires and

can cause damage to the circuit and appliances.

c) Short circuit :-

Short circuit is caused when the live wire and neutral wire comes in contact and the current suddenly

increases in the circuit. It causes spark, fire and damage to the circuit and appliances.

3. Explain Direct and Alternating current

Answer: a)Direct current (DC) :- A current that always flows in one direction only is called direct

current. The current we get from a battery is a direct current.

b) Alternating current (AC) :- A current that reverses its direction periodically is called alternating

current. Most power stations in our country produce alternating current. AC changes direction every

1/100 second and its frequency is 50 Hertz (Hz). One advantage of AC over DC is that it can be

transmitted over long

distances without much loss of energy

4. Draw the pattern of magnetic field lines of a current carrying solenoid. What does the pattern of

fieldlines inside the solenoid indicate? Write one application of magnetic field of current carrying

solenoid.

Figure 13.10 (Page No.229 NCERT Text Book)

Answer: Pattern of magnetic field lines It indicates that the magnetic field is the same at all points

inside the solenoid

Application-

For making an electromagnet

5 marks Questions & Answers of Magnetic Effects of Electric Currents

1. Explain with an experiment principle of Electromagnetic induction? Which law will gives the

direction of electric current?

Answer: The motion of a magnet with respect to a coil or a change in the magnetic field induce a

potential difference in the coil and produces induced current. This is called electromagnetic induction.

i) Motion of a magnet with respect to a coil produces induced current :-

If a magnet is moved towards or away from a coil of wire connected to a galvanometer, the

galvanometer needle shows a deflection. This shows that current is induced in the coil due to the

motion of the magnet.

Change in magnetic field produces induced current :-

Take two coils of wires wound around a cylindrical paper roll. Connect one coil to a battery and the

other coil to a galvanometer. If current is passed through the first coil, the galvanometer needle shows

a deflection in the second coil. If the current is disconnected, the needle moves in the opposite

direction. This shows that current is induced due to change in magnetic field.

Fleming’s Right Hand Rule :-

The direction of induced current is given by Fleming’s Right Hand Rule.

It states that ‘ If the thumb, fore finger and middle finger of the right hand is held perpendicular to

each other such that the thumb points in the direction of motion of the conductor, the fore finger

points in the direction of the magnetic field, then the middle finger shows the direction of induced

current ’.

2. Explain Domestic electric circuit?

Answer: Electric power to homes is supplied through the mains. It has two wires. One is a live wire

(positve wire) with red insulation and the other is a neutral wire (negative wire) with black insulation.

The potential difference between the two wires is 220V. The earth wire with green insulation is

connected to a metal plate kept in the ground.

Two separate circuits are used. One is of 15A for appliances with high power rating like gysers, air

conditioners etc. The other is of 5A for fans, bulbs etc. The different appliances are connected in

parallel so that every appliance gets equal voltage and even if one is switched off the others are not

affected.

The appliances having metallic body like electric iron, refrigerators etc., their metallic body is

connected to the earth wire so that if there is leakage of current, it passes to the earth and prevents

electric shock

3. Explain the meaning of the word ‘electromagnetic’ and ‘induction’ in the term electromagnetic

induction. On what factors does the value of induced current produced in a circuit depend? Name and

state the rule used for determination of direction of induced current. State one practical application of

this phenomenon in every day life.

Ans)

i) Meaning of the terms (1)

(ii) Rate of change of magnetic flux (1)

(iii) Fleming’s Right Hand Rule (1)

(iv) Statement of the rule (1)

(v) Electric Generator (1)

(v) Power can be transmitted over long distances without much loss of energy. 1

HOTS Questions with Answers

Magnetic Effects of Electric Currents

Q1.On what factors does the magnetic field intensity at the centre of the circular coil carrying

depend?

Answer: The magnetic field intensity at the centre of the circular coil is directly proportional to

current and inversely proportional to radius of the coil. So, in both the cases ,that is, twice the current

as well as half in radius, the magnetic field intensity gets doubled.

Q2.State the principle used to determine the force experienced by a conductor carrying current in

uniform magnetic field ?

Answer: .Fleming’s Left Hand Rule-Stretch the first three fingers of the left hand mutually

perpendicular to each other such that the fore finger points in the direction of magnetic field, the

middle finger points in the direction of current, then the thumb will indicate the direction of force

experienced by the conductor.

Q3.On what factors does the force experienced by a conductor carrying current in uniform magnetic

field depend?

Answer: .Force experienced by a conductor depends on

(a)Current and

(b)The perpendicular distance between that point and the conductor.

(c)Magnetic field strength

Q4.On what factors does the strength of a magnetic field at a point due to a straight conductor

carrying current depend ?

Answer:.(a)Magnitude of electric current and

(b)perpendicular distance between that point and the . Conductor.

Q5.Differentiate between direct current and alternating current.

Answer: .DIRECT ALTERNATING CURRENT CURRENT

(a)It has constant a) It varies in magnitude.

(b)It has constant b) It canges its direction direction alternatively

(c)It is less danger ous in terms of terms of shock. c) It is more dangerous in electic shock.

Q6.A switch is always connected in

(a)earth wire

(b)neutral wire

(c)live wire

Answer: . It is always connected with live wire.

Q7.What type of connection is used in household circuits?

Answer: .In household circuits all electrical appliances are connected in parallel.

Q8.State the principle of the working of an electric motor.

Answer: .An electric motor works on the principle of force experienced by a current carrying

conductor in a magnetic field. The two forces acting are equal and opposite. Since they act in

different lines the bring rotational motion.

Q9.State the principle of a D.C generator.

Answer: .It is based on the principle of electromagnetic induction.

Q10.State the characteristics of magnetic field lines.

Answer: ( i)The direction of magnetic field is indicated by the arrow in the line at any point

(tangent).

(ii)The field lines come out of the north pole and emerge into the south pole(closed loops are

formed). (iii)No two field lines will never ever intersect each other.

Q11.State Right Hand Thumb Rule.

Answer: .Hold the wire carrying current in your hand, such that the thumb points in the direction of

current, the direction of the curled fingers will indicate the the direction of magnetic field.

Q12.Define the phenomenon overloading.

Answer: .If the total current drawn by all the appliances at a particular time exeeds the bearing

capacity of that wire, the wires of the domestic wiring get heated.This Phenomenon is called

overloading.

Q.13. How can it be shown that magnetic field exist around a wire carrying current?

Answer: By using magnetic compass which, shows deflection.

A current-carrying straight conductor is placed in the east-west direction. What

Q.14 Will be the direction of the force experienced by this conductor due to earth’s magnetic field?

How will this force get affected on? (a) reversing the direction of flow of current (b) doubling the

magnitude of current.

The direction of earth’s magnetic field is from G-south to G-north.

Answer: Let current is from west to east. Therefore force is vertically upwards.

(a) By reversing the direction of current, the direction of will be reversed i.e.

vertically downwards.

(b) The magnitude of the force is doubled.

Q.15. A wire carrying current passes through the middle of the plane A perpendicular to it. If a

magnetic needle is placed in the plane parallel to the wire. What will be the direction of the needle?

Answer: (i) along the tangent to a circle going anti-clockwise to an out coming current( to plane A).

Q.16.A wire carrying current passes through the middle of the plane A perpendicular to it. If a

magnetic needle is placed in the plane perpendicular to the plane A, what will be the direction of the

needle? Answer: .Any direction, as the needle is not influenced by a perpendicular field.

Q.17.If a magnetic needle is placed at the north pole in a horizontal plane, in what direction it will

indicate? Why?

Answer: They will show random orientation as the magnetic field at the poles are along the vertical

line and not on the horizontal plane.

Q.18.If a magnetic needle is placed at the north pole in a vertical plane, what will be its direction?

Answer: .They will stand vertically.

Q.19. Is a circular coil carrying current similar to magnet?

Answer: Yes

Q.20. What is the role of soft iron in the core of a solenoid?

Answer: It acts as an electromagnet.

CLASS X Physics solved questions -Magnetic effects of electric current

(Q.) What is magnetic field?

(Ans) The region around the magnet, where force of attraction or repulsion can be felt by magnetic

materials, is called as magnetic field.

(Q.) What will be the frequency of an alternating current, if its direction changes after every 0.05 s?

(Ans) The time period (T) of one cycle would be = 2 x (0.05 s) = 0.1 s.

frequency, f = 1/T. Hence, f = (1 / 0.1) = 10 Hz.

(Q.) What is the principle on which working of electric generator is based? What are its important

parts?

(Ans) The working of electric generator is based on the principle of electromagnetic induction.

Important parts of electric generator are armature, slip rings, brushes and field magnets.

(Q.) Why two magnetic lines of force don’t intersect each other?

(Ans) If so then at the point of intersection there will be two different directions of magnetic field

which is not possible.

(Q.) Give two methods by which we can increase the strength of magnetic field produced by a

circular coil carrying current?

(Ans) The two methods by which we can increase the strength of magnetic field are given below:-

1. By increasing the number of turns of wire in the coil.

2. By increasing the current flowing through the coil.

(Q.) What are the patterns of magnetic field lines inside and outside of a solenoid? What do they

indicate?

(Ans) (i)The field lines inside the solenoid are parallel straight lines. This indicates that the magnetic

field is uniform and is therefore, same at all points inside it.

(ii)The field lines outside the solenoid are curved lines. This indicates that the magnetic field is non-

uniform.

(Q.) What are the factors which govern the force experienced by a current carrying conductor placed

in a uniform magnetic field depends?

(Ans) The factors which govern the force expericed by conductor which is placed in a uniform

magnetic field are:-

1. strength of the magnetic field in which conductor is placed.

2. strength of current flowing through the conductor.

3. length of conductor.

(Q.) Distinguish between an electric motor and generator?

(Ans) The major differences between an electric motor and generator are stated below:

Electric Motor Generator

1. It converts electrical energy into mechanical energy.

2. It needs electrical energy for its working.

3. They are used as water pumps, marble grinders e.t.c

Generator

1. It converts mechanical energy into electrical energy

2. It needs mechanical energy for its working.

3. They are used as water pumps, marble grinders e.t.c

3. Diesel generator, hydro-electric generator are the examples of it.

(Q.) Why mostly all electrical home appliances like refrigerator, toaster etc. are provided with a wire

having green insulation?

(Ans) Earth wire is the insulated green coloured copper wire which is connected to a metal plate deep

inside the earth near the house. It is used as a safety measure.

It is kept at zero potential by connecting it to the ground, thus, providing a low-resistance conducting

path for the current.

When by electric fault, if current flows through the metallic body of electric appliance and we touch

it, then current finds the lower resistance path of earth wire than our body. So, current flows through

earth wire only and we remain safe.

(Q.) Describe domestic household circuit.

(Ans) From an electric pole or underground cables, we receive electric supply in our homes.

Domestic electric circuit consists of three main wires.The wire with red insulation is called live wire.

The wire with black insulation is called neutral wire. Potential difference between the neutral and the

live wire is 220 V.

The wire with green insulation is called earth wire. It is connected to a metallic body deep inside the

earth.

According to new International Convention, insulation of live wire should be of brown colour

whereas neutral and earth wires should be of light blue and green (or yellow) insulation cover. In our

homes, we receive AC electric power of 220 V with a frequency of 50 Hz. Live wire and neutral wire

maintains the p.d. of 220 V. These wires pass through the fuse board. Fuse is specially connected

with the live wire. Current rating of this fuse depends on house load. From the fuse board, these wires

pass through the electric metre. From the metre, the earth wire is locally inserted inside the ground of

the house. After the electric metre, these wires pass through the main switches and fuses in different

rooms. Depending on the power of electrical appliances, two types of fuse (5A or 15 A) are used.

From the switch and fuse board, the power lines are distributed to different electrical appliances.

(Q.) Describe about short circuiting and overloading in detail.

(Ans) Short Circuiting: Short-circuiting occurs in a circuit when the live wire comes in direct contact

with the neutral wire. This causes much damage to the electric appliances connected with them.

Reason of short-circuiting: When the live wire touches the neutral wire, the contact portion of the two

wires behave like load and due to very low resistance of copper wire, it draws very large amount of

current. In the presence of this high current, the copper wire catches fire, due to joules heating effect.

Overloading: Overloading occurs in a circuit when the current in the circuit increases abruptly. It

causes overheating of the wire and might lead to the fire. It can also occur due to accidental increase

in the supply voltage or on connecting too many appliances to a single socket.

(Q.) What is an electromagnet? On what factors its magnetic field depends? Mention the differences

between an electromagnet and a permanent magnet.

(Ans) Electromagnet is a magnet formed by the magnetization of a piece of a magnetic material (such

as soft iron) by inserting it into a solenoid. The magnetic field (strength) of an electromagnet depends

upon:

(i) Amount of current passing through the coil (ii) Number of turns of the coil

(iii) Nature of core material present inside coil

Differences between electromagnet and permanent magnet are:

Electromagnet Permanent Magnet

1.It is temporary magnet and can be demagnetized. 1.It is a permanent magnet and cannot be

demagnetized easily.

2.Magnetic strength can be changed. 2. Its strength is fixed.

3.Its polarity can also be changed. 3.Its polarity is fixed.

4.It is prepared from soft iron. 4.It is prepared from hard steel.

(Q.) What do you understand by magnetic effect of electric current?

(Ans) The phenomenon due to which, a wire behaves like a magnet when electric current is passed

through it, is called as the magnetic effect of electric current.

(Q.) Explain Maxwell's right hand thumb rule?

(Ans) According to Maxwell's right hand thumb rule,

“If we hold the current-carrying conductor in our right hand in such a way that the thumb is stretched

along the direction of the current, then the curled fingers give the direction of the magnetic field

produced by the current”,

(Q.) What are the properties of magnetic field due to a current through a straight wire?(Ans) The

properties of magnetic field due to a current through a straight wire are:

1. The magnitude of the magnetic field produced at a given point increases as the current through the

wire increases.

2. The magnetic field produced by a given current in the conductor decreases as the distance from it

increases.

3. The concentric circles representing the magnetic field around a current-carrying straight wire

become larger and larger as we move away from it.

4. If the direction of the current is reversed in the wire, the lines will still be circular, but the

directions of the lines will be reversed, which can be verified using the compass needle.

(Q.) Which rule is used find the direction of the force on a conductor in a magnetic field.

Explain?Ans) To find the direction of the force on a conductor in a magnetic field, a simple rule

known as Fleming's left-hand rule is used.

According to Fleming's left-hand rule, if you stretch the thumb, forefinger and middle finger of your

left hand such that they are mutually at right angles, If the First finger points in the direction of the

field. The second finger represents the direction of the current (in the classical direction, from

positive to negative), then the thumb will point in the direction of the force acting on the conductor or

in the direction of the resultant motion. Thish rule is used to know the direction of the induced current

Q. Give characteristics of magnetic field lines.

Ans: (i) They represent the magnetic field.

(ii) They are directed from north to South Pole outside a magnet and from south to North Pole inside

a magnet.

(iii) The field lines are closed curves.

(iv) The strength of magnetic field in a region is determined by closeness of the field lines in that

region.

(v) The closer the field lines are, greater will be the field strength and vice–versa.

(vi) No two field lines ever cross each other as it would mean two different directions of field at point

of intersection, which is not possible.

(viii) The parallel lines represent the uniform magnetic field whereas converging lines or diverging

lines represents the non uniform magnetic field.

Q.) What do you mean by electromagnetic induction?

(Ans) "The process, due to which a changing magnetic field in a conductor induces a current in

another conductor, is called electromagnetic induction".

Q. A current through a horizontal power line flows in north to south direction.What is the direction of

magnetic field (i)at a point directly below it and (ii)at a point directly above it?

Ans. (i) West to East (ii) East to West

Q. A straight wire carrying electric current is moving out of plane of paper and is perpendicular to it.

What is the direction and type of induced magnetic field?

Ans . Induced magnetic field will be in the form of concentric circles in the plane of paper.

Q. How can it be shown that magnetic field exist around a wire carrying current?

Ans:By using magnetic compass which, shows deflection.

Q. How can a solenoid be used to magnetise a steel bar.

Ans :By inserting the steel bar inside the solenoid and switching on electric current.

Q. Can a 5 A fuse be used in wire carrying 15 A current? Why?

Ans:No, because both of them would then be ineffective in controlling the amount of current flowing.

Q. Give the factors that affect strength of magnetic field at a point due to a straight conductor

carrying current.

Ans : Magnitude of electric current, perpendicular distance between that point and conductor.

Q. Where do we connect a fuse: with live wire or with neutral wire?

Ans: It is always connected with live wire.

Q. Give two uses of electromagnets.

Ans: (i) It is used in cranes for lifting heavy loads.

(ii) used in electric bells.

Q. Name any two devices which use permanent magnets.

Ans: Loudspeakers, Galvanometer, voltmeter.

Q. A current-carrying straight conductor is placed in the east-west direction. What will be the

direction of the force experienced by this conductor due to earth’s magnetic field? How will this force

get affected on? (a) reversing the direction of floe of current (b) doubling the magnitude of

current.Ans .11 The direction of earth’s magnetic field is from G-south to G-north. Let current

is from west to east. Therefore force is vertically upwards.

(a) By reversing the direction of current, the direction of will be reversed i.e.

vertically downwards.

(b) The magnitude of the force is doubled.

Q. An electron enters a magnetic field at right angles to it as shown in fig. The direction of the force

acting on the electron will be:

(a) to the right (b) to the left (c) out of the page (d) into the pageAns .

12 When a conductor carrying current is placed perpendicular to the direction of magnetic field, the

acting on it is given by Fleming’s left hand rule. Since the direction of current is the same as that of

the motion of a positive charge, the d irection of force acting on it when moving perpendicular to the

direction of magnetic field is the same as that acting on a current-carrying conductor placed

perpendicular to the direction of magnetic field. Obviously, the force acting on an electron is opposite

to that. Therefore in this case it is into the page.

Q. A coil of insulated copper wire is connected to a galvanometer. What would happen if a bar

magnet is (i) Pushed into the coil? (ii) Withdrawn from inside the coil? (iii) Held stationary inside the

coil?

Ans (i) Due to change in magnetic flux linked with coil, the galvanometer shows deflection (say

towards right).

(ii) Due to change in magnetic flux linked with coil, the galvanometer shows deflection (say towards

left opposite to that in case one).

( ii i) As it is stationary no change in magnetic flux linked with coil, so galvanometer shows no

deflection.

Q.A magnetic compass needle is placed in the plane of paper near point A as shown in Figure 13.6. In

which plane should a straight current carrying conductor be placed so that it passes through A and

there is no change in the deflection of the compass? Under what condition is the deflection maximum

and why?Ans: In the plane of the paper itself. The axis of the compass is vertical and the field due to

the conductor is also vertical. It could result in a dip of compass needle which is not possible in this

case (dips result only if axis of compass is horizontal). The deflection is maximum when the

conductor through A is perpendicular to the plane of paper and the field due to it is maximum in the

plane of the paper

Q. Under what conditions permanent electromagnet is obtained if a current carrying solenoid is

used?

Ans: (i) The current through the solenoid should be direct current.

(ii) The rod inside is made of a magnetic material such as steel

Q. It is established that an electric current through a metallic conductor produces a magnetic field

around it. Is there a similar magnetic field produced around a thin beam of moving (i) alpha particles,

(ii) neutrons? Justify your answer.Ans: (i) Yes, Alpha particles being positively charged constitutes a

current in the direction of motion.

(ii) No. The neutrons being electrically neutral constitute no current.

Q. Meena draws magnetic field lines of field close to the axis of a current carrying circular loop. As

she moves away from the centre of the circular loop she observes that the lines keep on diverging.

How will you explain her observation.

Ans: Strength of the magnetic field falls as distance increases. This is indicated by the decrease in

degree of closeness of the lines of field.

Q. What does the divergence of magnetic field lines near the ends of a current carrying straight

solenoid indicate?

Ans: The divergence, that is, the falling degree of closeness of magnetic field lines indicates the fall

in strength of magnetic field near and beyond the ends of the solenoid.

Q. What is the role of the two conducting stationary brushes in a simple electric motor?

Ans: The brushes are connected to the battery and touch the outer side of two halves of the split ring

whose inner sides are insulated and attached to the axle.

Q. What is the difference between a direct current and an alternating current? How many times does

AC used in India change direction in one second?

Ans: Direct current always flows in one direction but the alternating current reverses its direction

periodically. The frequency of AC in India is 50 Hz and in each cycle it alters direction twice.

Therefore AC changes direction 2 × 50 = 100 times in one second.

Q.What is the role of fuse, used in series with any electrical appliance? Why should a fuse with

defined rating not be replaced by one with a larger rating?

Ans: Fuse is used for protecting appliances due to short-circuiting or overloading. The fuse is rated

for a certain maximum current and blows off when a current more than the rated value flows through

it. If a fuse is replaced by one with larger ratings, the appliances may get damaged while the

protecting fuse does not burn off. This practice of using fuse of improper rating should always be

avoided

(Q.) What is the principle behind the working of electric generator? Explain its working with the help

of well labeled diagram.

(Ans) Principle of working (Electric generator): The electric generator works on the principle that

when a conductor is moved in a magnetic field then current is induced in the conductor. The direction

of the induced current is given by Fleming’s left hand rule.

Construction and Working: The construction of a simple electric generator is shown in the figure

below:

It has a rectangular coil which is placed between two strong horse-shoe magnets. On the periphery of

coil large turns of insulated copper wire is wound.

Here the ends A and D of the coil are connected to slip rings R1 and R2. They rotate along with the

coil, while two carbon brushes B1 and B2 keep contact with them.

Suppose coil starts rotating in the clockwise direction than current is induced in the coil, which flows

from points ABCD. The direction of current is given according to the Flemings left hand rule.

After half rotation of the coil, arm CD starts moving up while AB starts moving down. Now the flow

current induced is reversed, that is current flows through DCBA. Hence we may say that after every

half cycle direction of flow of current is reversed. Because of this reason the current produced by the

generator is also called as alternating current.

(Q.) Explain the construction and working of electric motor?

(Ans) Construction: An ordinary electric motor consists of an armature ABCD (a coil of large number

of turns) wound on an iron core.The armature is placed in a strong magnetic field.The ends of the

armature are connected to two halves (P and Q) of a split ring.In electric motors, the split ring acts as

a commutator (a device that reverses the direction of flow of current through a circuit is called

commutator). P and Q are in contact with carbon brushes X and Y, respectively.The carbon brushes

are then connected to a battery and a key.

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Working: As soon as the key is closed, the current in arm AB of the coil flows from A to B and the

current in arm CD flows from C to D.According to Fleming’s Left-Hand Rule, the arm AB will move

downwards while the arm CD will move upwards, resulting in the anticlockwise movement of the

armature along with the split ring. As soon as the armature ABCD reaches its vertical position while

rotating, the current through the coil is cut off as the brushes (X and Y) touch the gap between P and

Q. The coil does not stop rotating as it has gained momentum and it goes beyond the vertical position.

When coil goes beyond vertical position, the direction of current along the arms AB and CD is

reversed .Therefore, the direction of force acting on AB and CD gets reversed. Now, AB moves up

and CD goes down. Again, due to momentum, the armature continues its anticlockwise rotation.

Finally, the coil reaches its initial position. The cycle continues as long as there is flow of electric

current through the armature. An axle can be attached to the rotating split ring which can be used to

do work.

Q. Why does a magnetic compass needle pointing North and South in the absence of a nearby magnet

get deflected when a bar magnet or a current carrying loop is brought near it. Describe some salient

features of magnetic lines of field concept.

Ans: Current carrying loops behave like bar magnets and both have their associated lines of field.

This modifies the already existing earth’s magnetic field and a deflection results. Magnetic field has

both direction and magnitude. Magnetic field lines emerge from N-pole and enter Spole. The

magnetic field strength is represented diagrammatically by the degree of closeness of the field lines.

Field lines cannot cross each other as two values of net field at a single point cannot exist. Only one

value, a unique net value, can exist. If in a given region, lines of field are shown to be parallel and

equispaced, the field is understood to be uniform.

CLASS X Important Questions Bank Magnetic effects of electric current

One mark Questions:

Part 1

1. How can you show that the magnetic field produced by a given electric current in the wire

decreases as the distance from the wire decreases?

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2. What is the advantage of the third wire of earth connection in domestic appliances?

3. What constitutes the field of a magnet?

4. What is short-circuiting in an electric supply?

5. What will be the frequency of an alternating current if its direction changes after every 0.01s?

6. An alternating electric current has a frequency of 50 Hz. How many times does it change its

direction in 1s?

7. How is the strength of the magnetic field at a point near a wire related to the strength of the electric

current flowing in the wire?

8. How can it be shown that a magnetic field exists around a wire through which a direct current is

passing?

9. On what effect of an electric current does an electromagnet work?

10. What is the direction of magnetic field at the centre of a circular coil carrying current in

anticlockwise direction?

Part -2

(Q.1) Passage of current through a straight conductor display some fixed pattern. Pick out the odd one

( 1 mark )

(a) Magnitude of the magnetic field produced at a given point increases as the current through wire

increases

(b) The magnetic field produced by a given current in the conductor increases as the distance from it

decreases

(c) Direction of the field lines is in accordance with the right hand thumb rule

(d) Field lines are unaffected by the quantity of current flowing.

(Q.2) The phenomenon of electro-magnetic induction is ( 1 mark )

(a) The process of generating magnetic field due to a current passing through a coil.

(b) Producing induced current in a coil due to relative motion between the magnet and the coil.

(c) The process of rotating a coil.

(d) The process of charging a body.

(Q.3) A magnetic field cannot exert any force on a( 1 mark )

(a) Moving magnet

(b) Stationary magnet

(c) Stationary charge

(d) Moving charge

(Q.4) Degree of closeness of the magnetic field lines signifies:( 1 mark )

(a) Number of magnetic fields

(b) Distance between different magnetic fields

(c) Relative strength of the magnetic field

(d) Direction of the magnetic field

(Q.5) What is a magnet? ( 1 mark )

(Q.6) What is the SI unit of induced current? ( 1 mark )

(Q.7) What is the frequency of d.c current? ( 1 mark )

(Q.8) What is the frequency of a.c current that you use in your house? ( 1 mark )

(Q.9) What is magnetic field? ( 1 mark )

(Q.10) There is a battery operated toy, what kind of motor is being used in it? ( 1 mark )

(Q.11) Give two example of devices in which d.c motor is used. ( 1 mark )

(Q.12) Give two examples in which a.c motor is used. ( 1 mark )

(Q.13) What is generator? ( 1 mark )

(Q.14) What is motor? ( 1 mark )

(Q.15) When the current in a wire moves from south to north, the direction of the deflection in the

magnetic needle parallel to the wire will be:( 1 mark )

(a) East to west

(b) West to east

(c) East to north

(d) West to south

(Q.16) Magnetic field is a quantity that has both direction and magnitude. Pick out the incorrect

statement( 1 mark )

(a) The magnetic field lines emerge from north pole and merge at the south pole.

(b) Inside the magnet, the direction of field lines is from its south pole to its north pole.

(c) Inside the magnet, the direction of field lines is from its north pole to its south pole.

(d) No two field lines intersect each other and the field is strongest where the field lines are crowded.

(Q.17) The region surrounding a magnet, in which the force of the magnet can be detected is said to

have( 1 mark )

(a) Magnetic field

(b) Electric field

(c) Magnetic poles (d) Electric poles

(Q.18) Which of the following is not the special features of magnets? ( 1 mark )

(a) They align in the North –South direction when suspended freely.

(b) They have two distinct North and South poles.

(c) Like poles attract each other and unlike poles repel each other.

(d) The magnetic field lines produced due to a magnet are closed curves.

(Q.19) Direction of the force experienced by a current-carrying conductor when placed in a magnetic

field is dependent on ( 1 mark )

(a) Direction of the current alone

(b) Direction of the magnetic field alone

(c) Direction of current as well as the direction of magnetic field

(d) Direction of electric field

(Q.20) The magnitude of the force experienced by a current-carrying conductor when placed in a

magnetic field will be( 1 mark )

(a) Maximum if the directions of current and magnetic field are perpendicular to each other

(b) Minimum if the directions of current and magnetic field are perpendicular to each other

(c) Maximum if the directions of current and magnetic field are opposite to each other (d) Maximum

if the directions of current and magnetic field are same

(Q.21) Which of the following is not true for an electric generator( 1 mark )

(a) Converts mechanical energy into electrical energy.

(b) Works on the basis of electromagnetic induction.

(c) Can be used to generate AC or DC.

(d) Converts electrical energy to mechanical energy

(Q.22) An alpha particle is projected towards west and gets deflected towards north by a magnetic

field. The direction of the magnetic field is ( 1 mark )

(a) Towards south

(b) Towards east

(c) Downwards

(d) Upwards

(Q.23) An electric current through a metallic conductor produces a/an _________ around it. ( 1 mark

)

(a) Electric field

(b) Magnetic field

(c) Electromagnetic effect.

(d) Gravitational field

(Q.24) A straight conducting wire is placed parallel to and over a compass needle. The deflection in

the needle ( 1 mark )

(a) Becomes opposite when the direction of the current is reversed

(b) Remains in the same direction even on reversing the direction of current

(c) Keeps fluctuating on passage of current in any direction

(d) Is negligible on reversing the direction of current

(Q.25) At every point of a current carrying circular loop, the concentric circles representing the

magnetic fields around it would become( 1 mark )

(a) Larger and larger as we move away from the wire.

(b) So large at the centre of circular loop that they look like straight lines.

(c) Smaller and smaller as we go away from the wire.

(d) There is no fixed pattern for circles

(Q.26) Which of the following statements is not true?( 1 mark )

(a) The pattern of the magnetic field around a conductor due to an electric current flowing through it

depends on the shape of the conductor.

(b) The magnetic field of a solenoid carrying a current is similar to that of a bar magnet.

(c) Magnitude of magnetic field is directly proportional to the quantity of current flowing through the

current.

(d) Magnetic field produced by the passage of current through a straight wire is permanent.

(Q.27) Magnetic field produced inside a solenoid are so strong that ( 1 mark )

(a) They can be used to magnetize a magnetic material, when placed inside the coil.

(b) They can be used to magnetize a magnetic material, when placed near the coil.

(c) They are still not able to magnetize a magnetic material.

(d) They become permanent.

(Q.28) Increase in number of turns of a coil in the solenoid will( 1 mark )

(a) Have no effect on the strength of magnetic field

(b) Will add to the strength of the magnetic field

(c) Will decrease the strength of the magnetic field

(d) Will change the direction of the magnetic field

(Q.29) An electromagnet consists of a core of ___________ wrapped around with a coil of ________

copper wire.( 1 mark )

(a) Soft iron, insulated

(b) Aluminum, Insulated

(c) Soft iron, uncovered

(d) Magnet, uncovered

(Q.30) A current-carrying conductor when placed in a magnetic field experiences ( 1 mark )

(a) An acceleration

(b) A force

(c) Demagnetization

(d) It always remains in equilibrium

(Q.31) An electric motor is a device( 1 mark )

(a) That converts electrical energy into kinetic energy

(b) That converts electrical energy to mechanical energy

(c) There is no energy conversion of one form to another.

(d) That converts sound energy to light energy.

(Q.32) Which of the following statements cannot be related to the construction of an electric motor? (

1 mark )

(a) A rectangular coil of insulated copper wire is placed between the two poles of a magnetic field

such that two of its parallel sides are perpendicular to the direction of the magnetic field.

(b) The ends of the coil are connected to the two halves of a split ring.

(c) The inner insulated sides are attached to axle whereas the external conducting edges touch two

conducting stationary brushes.

(d) The coil and the axle continuously rotate in one direction.

(Q.33) The direction of the induced current is given by( 1 mark )

(a) Right Hand Thumb Rule

(b) Fleming’s Left Hand Rule

(c) Fleming’s Right hand Rule

(d) Faraday's law

(Q.34) According to Fleming’s Right Hand Rule, if we stretch the thumb, forefinger and middle

finger of right hand – forefinger indicates direction of magnetic field, thumb shows the direction of

motion of conductor, and then the middle finger will show the direction of ( 1 mark )

(a) Induced current

(b) Magnetic Force

(c) Alternating Current

(d) Electric force

(Q.35) The induced current is highest when ( 1 mark )

(a) Direction of motion of coil is at 900 to the magnetic field.

(b) Direction of motion of coil is at 300 to the magnetic field.

(c) Direction of motion of coil is at 600 to the magnetic field.

(d) Direction of motion of coil is at 1800 to the magnetic field.

(Q.36) Parameters of electricity supply in India are ( 1 mark )

(a) Potential Difference of 220 V, Frequency of 50 hertz and Current Rating of 5A/15A

(b) Potential Difference of 150 V, Frequency of 40 hertz and Current Rating of 10 A

(c) Potential Difference of 220 V, Frequency of 60 hertz and Current Rating of 15A

(d) Potential Difference of 220 V, Frequency of 40 hertz and Current Rating of 5 A

(Q.37) Pick the incorrect statement regarding fuse. Fuse is used for protecting the circuits due to ( 1

mark )

(a) Short-circuiting

(b) Overloading of circuits

(c) Faulty connections

(d) Theft

(Q.38) Which of the following will not cause overloading? ( 1 mark )

(a) Accidental hike in the supply voltage

(b) Connecting many appliances to a single socket

(c) Melting of fuse

(d) Short circuiting

Two marks Questions:

1. With the help of a neat-diagram, describe how you can generate induced current in a circuit.

2. What is meant by the term “Magnetic field Lines”? List two properties of magnetic field lines.

3. Write the rule which determines the direction of magnetic field developed around a straight

conductor when current is passed through the conductor.

4. State the rule to determine the direction of magnetic field produced around a current carrying

conductor.

5. On which factors does the force experienced by a current carrying conductor placed in a uniform

magnetic field depend?

6. State Fleming’s right-hand Rule.

7. Why is series arrangement not used for domestic circuits?

8. Differentiate between electric force and magnetic forces.

9. How does AC differ from DC? What are the advantages and disadvantages of AC over DC?

10. Draw the magnetic field due to a current carrying circular coil. State the clock rule to find the

polarities of the faces of the coil.

11. What will be the frequency of an alternating current, if its direction changes after every 0.05 sec?

12.What is the principle on which working of electric generator is based? What are its important

part?.

13.Why two magnetic lines of forces don’t intersect each other?

14. Give two methods with which we can increase the strength of magnetic field produced by a


Three Mark Questions

1. Draw the pattern of field lined due to a solenoid carrying electric current. Mark the north and the

south poles in the diagram.

2. Draw the pattern of lines of force due to a magnetic field through and around a current carrying

loop of wire. How would the strength of the magnetic field produced at the centre of the circular loop

be affected if (i) the strength of the current passing through this loop is doubled? (ii) the radius of the

loop

is reduced to half of the original radius?

3. Draw the pattern lines of force due to a magnetic field associated with a current carrying

conductor. State how the magnetic field produced changes (i) with an increase in current in the

conductor and (ii)

the distance from the conductor.

4. Draw the pattern of field lines due to a bar magnet. Mention any two properties of the magnetic

field

lines.

5. How does the strength of the magnetic field at the centre of a circular coil of wire depend on: (i)

the

radius of the coil? (ii) the number of turns of the wire? (iii) the strength of the current flowing in the

coil?

6. The flow of a current in a circular loop of a wire creates a magnetic field at its centre. How can

existence of the field be detected? State the rule which helps to predict the direction of this magnetic

field.

7. What are the factors on which the strength of magnetic field produced by current-carrying

solenoid

depends?

8. A coil of copper wire is connected to a galvanometer. What would happen if a bar magnet is: (i)

pushed into the coil with north pole entering first (ii) pulled out of the coil (iii) held stationary inside

the coil?

9. Explain what is short-circuiting and overloading in an electric supply.

10. What are magnetic field lines? How is the direction of a magnetic field at a point determined?

Mention two important properties of the

11.What are the factors which govern the force experienced by a current carrying conductor placed in

a

uniform magnetic field depends? ( 3 Marks )

12. Distinguish between an electric motor and generator?

13.What is direct current (d.c) and alternating current (a.c).

14.A current of 2 A flows through a circular coil of radius of 4 cm, and has 10 turns. The coil is

aligned horizontally and current flows though the coil in clockwise direction. Find the magnitude and

direction of magnetic field at the centre of the coil due to the current.

Five Mark Questions:

1. (a) Suggest an activity to show the pattern of magnetic field lines, when you are provided with a

bar magnet, a cardboard piece and iron filings.(b)Draw a rough sketch of the field lines which you

will observe.

2. (a) What is an electromagnet? What does it consists of? (b) Name one material in each case used to

make a (i) permanent magnet (ii) temporary magnet. (c) Describe an activity to show how can you

make an electromagnet in your school lab?

3. State Fleming’s left-hand rule. With a labeled diagram, describe the working of an electric motor.

What is the function of split-ring Commutator in a motor?

4. State Fleming’s right-hand rule. With a labeled diagram, describe the working of an AC electric

generator.

5. Draw the lines of force of the magnetic field through and around (a)single loop of wire carrying

current, (b) a solenoid carrying electric current.

6. Why is pure iron not used for making permanent magnets? Name one material used for making

permanent magnets. Describe how permanent magnets are made electrically. State two examples of

electrical appliances made by using permanent magnets.

7. (a)Draw a schematic labeled diagram of a domestic wiring circuit which includes (i)a main fuse (ii)

a power meter (iii)one light point (iv) a power plug.(b) Why is it necessary to connect an earth wire to

electric appliances having metallic covers?

8. (a)What are magnetic field lines? How is the direction of a magnetic field at a point determined?

(b) Draw two field lines around a bar magnet along its length on its two sides and mark the field

directions on them by arrow marks. (c) List any three properties of magnetic field lines.

9. What is an electric motor? With the help of a diagram, describe the working of an electric motor.

10. What are magnetic field lines? Write their characteristics. Draw the magnetic field lines due to a

current flowing in a circular coil.

11. Explain the principle, construction and working of an electric motor.

12. Explain with labeled diagram, the principle, construction and working of an electric generator.

13. (a ). What is an electromagnet ?

(b). List any of its two uses.

(c ). Draw a labeled diagram to show how an electromagnet is made.

(d ). What is the purpose of the soft iron core used in making an electromagnet ?

14.A solenoid is 1 m long and 2 cm in diameter has 50 turns/cm. A current of 5 A is flowing through

it. Calculate the magnetic induction:

a) Inside the solenoid.

b) At one end on the axis of solenoid.

15. Explain the construction and working of electric motor?

16. What is the principle behind the working of electric generator? Explain its working with the help


17. The mains power supply of a house is through a 5-A fuse. How many 100-W bulbs can be used in

this house at the correct voltage?

18. A wire 10 cm long and carrying a current of 1.5 A is held in a uniform magnetic field in which

B=10-3 T. Calculate the force on the wire if it is held perpendicular to the lines of the magnetic field.

19 A current of 10 A flows in a circular coil of 1000 turns and radius 0.1 m. Find the magnitude of

the magnetic field at the centre of the coil.

20. At what distance from a straight conductor carrying a current of 2.8 A, will the magnetic

induction be 2.8×10-5 T?

21. Find the strength of the current which will produce a magnetic field of 10-4 T at the centre of a

coil of mean radius 0.10 m. The coil comprises 20 turns.

22. A 0.4 m wire, stretched horizontally, carries an electric current of 15 A from East to West, in a

magnetic field whose magnetic field intensity is 0.1 N/Am, directed vertically downwards. What is

(a) the magnitude of the magnetic deflecting force on the wire, and (b) its direction?

Magnetic effect of current cbse test paper-1

Questions from Board Exam Papers and CBSE Sample Papers

Chapter 13- Magnetic Effects of Electric Current

1. What is a magnetic field? What are field lines around a magnet?

2. List the characteristic properties of magnetic field lines.

3. Sketch the pattern of magnetic field lines around a bar magnet.

4. Sketch the pattern of magnetic field lines around a current-carrying straight conductor and state the

factors on which the strength of magnetic field depends.

5. State right hand thumb rule to find the direction of magnetic field around a current –carrying

straight conductor. How will this magnetic field be affected on (a) Increasing the current through the

conductor.

(b) Changing the direction of flow of current in the conductor.

6. A student performs an experiment to study the magnetic effect of current around a current-carrying

straight conductor. He reports that (a) The direction of deflection of the north pole of the compass

needle kept at a given point near the conductor remains unaffected even when the terminals of the

battery sending current in the wire are interchanged. (b) For a give battery, the degree of deflection of

N pole decreases when the compass is kept at a farther away from the conductor. Which of the above

observations of the student is incorrect and why?

7. Describe with a neat diagram an activity to show that a straight conductor carrying direct current

produces a magnetic field around it. State the rule which determines the direction of magnetic field

thus produced.

8. Draw the lines of force (indicating the direction) of magnetic field through and around (a) a single

loop of wire carrying direct current. (b) a solenoid carrying direct current.

9. What are the factors on which the magnetic field due to a current-carrying circular coil depends?

Also explain the pattern of field lines produced in and around a circular coil.

10. Draw the pattern of magnetic field lines of a current-carrying solenoid. What does the pattern of

field lines inside a solenoid indicate? Write one application of magnetic field of current-carrying

solenoid.

11. What is an electro-magnet? Draw a diagram showing an electro-magnet.

12. The magnetic field in a given region is uniform. Draw a diagram to represent it.

13. (a) Describe with diagram an experiment to show that a force is exerted on a current-carrying

conductor when placed perpendicular in a magnetic field. (b) State the rule to find the direction of the

force exerted on a current-carrying conductor in a magnetic field. (c) A current-carrying straight

conductor is placed in the East-West direction. What will the direction experienced by the conductor

due to earth’s magnetic field?

14. Why does a current-carrying conductor kept in a magnetic field experience force? On what factors

does the direction of this force depend? Name and state the rule used for determination of direction of

this force.

15. With a labeled diagram, describe the construction and working of an electric motor. What is the

function of split ring commutator in a motor?

16. What is the use of a commutator? Name the component in an electric motor which acts as a

commutator.

17. What is an armature? Mention the alternative methods adopted in commercial motors to enhance

their power.

18. Explain the principle of an electric motor. Name some appliances in which the electric motor is

used.

19. A positively charged particle projected towards West is deflected towards North by a magnetic

field. What is the direction of the magnetic field?

20. Explain the meaning of the word “electro-magnetic” and “induction” in the term electro-magnetic

induction. On what factors does the value of induced current produced in a circuit depend? Name and

state the rule used for determination of direction of induced current. State one practical application of

this phenomenon in everyday life.

21. Why is electro-magnetic induction so called? A coil connected to a sensitive galvanometer is held

stationary. A bar magnet with its North Pole facing coil is moving towards the coil at a certain speed.

The galvano meter needle shows deflection of 10 divisions to towards right of the centre of the scale.

How will the reading on the galvanometer scale be affected if the south pole of the bar magnet facing

the coil is moved away at the same speed?

22. Describe an activity to demonstrate the phenomenon of electro-magnetic induction.

23. State Fleming’s right hand rule. How is this rule useful?

24. Explain different ways to induce current in a coil.

25. (a) With the help of a neat labeled diagram, explain the construction and working of an electric

generator. What is the function of bushes? (b) How does a D.C generator differ from that of A.C

generator?

26. How does A.C differ from D.C? Which sources produce alternating current? What is the

frequency of alternating current in India

27. Draw a schematic labeled diagram of a domestic electric circuit which includes a mains fuse, a

power meter, a light point, a fan and a power plug.

28. What do you mean by (a) short circuit and (b) overloading? What are the safety precautions taken

to avoid these problems in domestic electric circuits?

29. (a) An electrician put a fuse rating of 5A in that part of domestic electric circuit in which an

electric heater of rating 1.5kW, 220V is operating. What is likely to happen in this and why? What

change, if any, needs to be made? (b) You are given the following current time graphs from two

different sources. (i) Name the type of current in two cases. (ii) Identify any one source for each type

of these currents. (iii) What is the frequency of current in case II in India? (iv)Use above graphs to

write two differences between the current in two cases.

30. An electrician assembling a household circuit uses a long thick copper wire with green insulation

and a short wire made up of copper-tin alloy. What are the two wires called? Mention the importance

of each wire in an electric circuit. How are the two wires connected in the circuit?

Part -2

(Q.1) Passage of current through a straight conductor display some fixed pattern. Pick out the odd one

( 1 mark )

(a) Magnitude of the magnetic field produced at a given point increases as the current through wire

increases

(b) The magnetic field produced by a given current in the conductor increases as the distance from it

decreases

(c) Direction of the field lines is in accordance with the right hand thumb rule

(d) Field lines are unaffected by the quantity of current flowing.

(Q.2) The phenomenon of electro-magnetic induction is ( 1 mark )

(a) The process of generating magnetic field due to a current passing through a coil.

(b) Producing induced current in a coil due to relative motion between the magnet and the coil.

(c) The process of rotating a coil.

(d) The process of charging a body.

(Q.3) A magnetic field cannot exert any force on a( 1 mark )

(a) Moving magnet

(b) Stationary magnet

(c) Stationary charge

(d) Moving charge

(Q.4) Degree of closeness of the magnetic field lines signifies:( 1 mark )

(a) Number of magnetic fields

(b) Distance between different magnetic fields

(c) Relative strength of the magnetic field

(d) Direction of the magnetic field

(Q.5) What is a magnet? ( 1 mark )

(Q.6) What is the SI unit of induced current? ( 1 mark )

(Q.7) What is the frequency of d.c current? ( 1 mark )

(Q.8) What is the frequency of a.c current that you use in your house? ( 1 mark )

(Q.9) What is magnetic field? ( 1 mark )

(Q.10) There is a battery operated toy, what kind of motor is being used in it? ( 1 mark )

(Q.11) Give two example of devices in which d.c motor is used. ( 1 mark )

(Q.12) Give two examples in which a.c motor is used. ( 1 mark )

(Q.13) What is generator? ( 1 mark )

(Q.14) What is motor? ( 1 mark )

(Q.15) When the current in a wire moves from south to north, the direction of the deflection in the

magnetic needle parallel to the wire will be:( 1 mark )

(a) East to west

(b) West to east

(c) East to north

(d) West to south

(Q.16) Magnetic field is a quantity that has both direction and magnitude. Pick out the incorrect

statement( 1 mark )

(a) The magnetic field lines emerge from north pole and merge at the south pole.

(b) Inside the magnet, the direction of field lines is from its south pole to its north pole.

(c) Inside the magnet, the direction of field lines is from its north pole to its south pole.

(d) No two field lines intersect each other and the field is strongest where the field lines are crowded.

(Q.17) The region surrounding a magnet, in which the force of the magnet can be detected is said to

have( 1 mark )

(a) Magnetic field

(b) Electric field

(c) Magnetic poles (d) Electric poles

(Q.18) Which of the following is not the special features of magnets? ( 1 mark )

(a) They align in the North –South direction when suspended freely.

(b) They have two distinct North and South poles.

(c) Like poles attract each other and unlike poles repel each other.

(d) The magnetic field lines produced due to a magnet are closed curves.

(Q.19) Direction of the force experienced by a current-carrying conductor when placed in a magnetic

field is dependent on ( 1 mark )

(a) Direction of the current alone

(b) Direction of the magnetic field alone

(c) Direction of current as well as the direction of magnetic field

(d) Direction of electric field

(Q.20) The magnitude of the force experienced by a current-carrying conductor when placed in a

magnetic field will be( 1 mark )

(a) Maximum if the directions of current and magnetic field are perpendicular to each other

(b) Minimum if the directions of current and magnetic field are perpendicular to each other

(c) Maximum if the directions of current and magnetic field are opposite to each other (d) Maximum

if the directions of current and magnetic field are same

(Q.21) Which of the following is not true for an electric generator( 1 mark )

(a) Converts mechanical energy into electrical energy.

(b) Works on the basis of electromagnetic induction.

(c) Can be used to generate AC or DC.

(d) Converts electrical energy to mechanical energy

(Q.22) An alpha particle is projected towards west and gets deflected towards north by a magnetic

field. The direction of the magnetic field is ( 1 mark )

(a) Towards south

(b) Towards east

(c) Downwards

(d) Upwards

(Q.23) An electric current through a metallic conductor produces a/an _________ around it. ( 1 mark

)

(a) Electric field

(b) Magnetic field

(c) Electromagnetic effect.

(d) Gravitational field

(Q.24) A straight conducting wire is placed parallel to and over a compass needle. The deflection in

the needle ( 1 mark )

(a) Becomes opposite when the direction of the current is reversed

(b) Remains in the same direction even on reversing the direction of current

(c) Keeps fluctuating on passage of current in any direction

(d) Is negligible on reversing the direction of current

(Q.25) At every point of a current carrying circular loop, the concentric circles representing the

magnetic fields around it would become( 1 mark )

(a) Larger and larger as we move away from the wire.

(b) So large at the centre of circular loop that they look like straight lines.

(c) Smaller and smaller as we go away from the wire.

(d) There is no fixed pattern for circles

(Q.26) Which of the following statements is not true?( 1 mark )

(a) The pattern of the magnetic field around a conductor due to an electric current flowing through it

depends on the shape of the conductor.

(b) The magnetic field of a solenoid carrying a current is similar to that of a bar magnet.

(c) Magnitude of magnetic field is directly proportional to the quantity of current flowing through the

current.

(d) Magnetic field produced by the passage of current through a straight wire is permanent.

(Q.27) Magnetic field produced inside a solenoid are so strong that ( 1 mark )

(a) They can be used to magnetize a magnetic material, when placed inside the coil.

(b) They can be used to magnetize a magnetic material, when placed near the coil.

(c) They are still not able to magnetize a magnetic material.

(d) They become permanent.

(Q.28) Increase in number of turns of a coil in the solenoid will( 1 mark )

(a) Have no effect on the strength of magnetic field

(b) Will add to the strength of the magnetic field

(c) Will decrease the strength of the magnetic field

(d) Will change the direction of the magnetic field

(Q.29) An electromagnet consists of a core of ___________ wrapped around with a coil of ________

copper wire.( 1 mark )

(a) Soft iron, insulated

(b) Aluminum, Insulated

(c) Soft iron, uncovered

(d) Magnet, uncovered

(Q.30) A current-carrying conductor when placed in a magnetic field experiences ( 1 mark )

(a) An acceleration

(b) A force

(c) Demagnetization

(d) It always remains in equilibrium

(Q.31) An electric motor is a device( 1 mark )

(a) That converts electrical energy into kinetic energy

(b) That converts electrical energy to mechanical energy

(c) There is no energy conversion of one form to another.

(d) That converts sound energy to light energy.

(Q.32) Which of the following statements cannot be related to the construction of an electric motor? (

1 mark )

(a) A rectangular coil of insulated copper wire is placed between the two poles of a magnetic field

such that two of its parallel sides are perpendicular to the direction of the magnetic field.

(b) The ends of the coil are connected to the two halves of a split ring.

(c) The inner insulated sides are attached to axle whereas the external conducting edges touch two

conducting stationary brushes.

(d) The coil and the axle continuously rotate in one direction.

(Q.33) The direction of the induced current is given by( 1 mark )

(a) Right Hand Thumb Rule

(b) Fleming’s Left Hand Rule

(c) Fleming’s Right hand Rule

(d) Faraday's law

(Q.34) According to Fleming’s Right Hand Rule, if we stretch the thumb, forefinger and middle

finger of right hand – forefinger indicates direction of magnetic field, thumb shows the direction of

motion of conductor, and then the middle finger will show the direction of ( 1 mark )

(a) Induced current

(b) Magnetic Force

(c) Alternating Current

(d) Electric force

(Q.35) The induced current is highest when ( 1 mark )

(a) Direction of motion of coil is at 900 to the magnetic field.

(b) Direction of motion of coil is at 300 to the magnetic field.

(c) Direction of motion of coil is at 600 to the magnetic field.

(d) Direction of motion of coil is at 1800 to the magnetic field.

(Q.36) Parameters of electricity supply in India are ( 1 mark )

(a) Potential Difference of 220 V, Frequency of 50 hertz and Current Rating of 5A/15A

(b) Potential Difference of 150 V, Frequency of 40 hertz and Current Rating of 10 A

(c) Potential Difference of 220 V, Frequency of 60 hertz and Current Rating of 15A

(d) Potential Difference of 220 V, Frequency of 40 hertz and Current Rating of 5 A

(Q.37) Pick the incorrect statement regarding fuse. Fuse is used for protecting the circuits due to ( 1

mark )

(a) Short-circuiting

(b) Overloading of circuits

(c) Faulty connections

(d) Theft

(Q.38) Which of the following will not cause overloading? ( 1 mark )

(a) Accidental hike in the supply voltage

(b) Connecting many appliances to a single socket

(c) Melting of fuse

(d) Short circuiting

Two marks Questions:

1. With the help of a neat-diagram, describe how you can generate induced current in a circuit.

2. What is meant by the term “Magnetic field Lines”? List two properties of magnetic field lines.

3. Write the rule which determines the direction of magnetic field developed around a straight

conductor when current is passed through the conductor.

4. State the rule to determine the direction of magnetic field produced around a current carrying

conductor.

5. On which factors does the force experienced by a current carrying conductor placed in a uniform

magnetic field depend?

6. State Fleming’s right-hand Rule.

7. Why is series arrangement not used for domestic circuits?

8. Differentiate between electric force and magnetic forces.

9. How does AC differ from DC? What are the advantages and disadvantages of AC over DC?

10. Draw the magnetic field due to a current carrying circular coil. State the clock rule to find the

polarities of the faces of the coil.

11. What will be the frequency of an alternating current, if its direction changes after every 0.05 sec?

12.What is the principle on which working of electric generator is based? What are its important

part?.

13.Why two magnetic lines of forces don’t intersect each other?

14. Give two methods with which we can increase the strength of magnetic field produced by a


Three Mark Questions

1. Draw the pattern of field lined due to a solenoid carrying electric current. Mark the north and the

south poles in the diagram.

2. Draw the pattern of lines of force due to a magnetic field through and around a current carrying

loop of wire. How would the strength of the magnetic field produced at the centre of the circular loop

be affected if (i) the strength of the current passing through this loop is doubled? (ii) the radius of the

loop

is reduced to half of the original radius?

3. Draw the pattern lines of force due to a magnetic field associated with a current carrying

conductor. State how the magnetic field produced changes (i) with an increase in current in the

conductor and (ii)

the distance from the conductor.

4. Draw the pattern of field lines due to a bar magnet. Mention any two properties of the magnetic

field

lines.

5. How does the strength of the magnetic field at the centre of a circular coil of wire depend on: (i)

the

radius of the coil? (ii) the number of turns of the wire? (iii) the strength of the current flowing in the

coil?

6. The flow of a current in a circular loop of a wire creates a magnetic field at its centre. How can

existence of the field be detected? State the rule which helps to predict the direction of this magnetic

field.

7. What are the factors on which the strength of magnetic field produced by current-carrying

solenoid

depends?

8. A coil of copper wire is connected to a galvanometer. What would happen if a bar magnet is: (i)

pushed into the coil with north pole entering first (ii) pulled out of the coil (iii) held stationary inside

the coil?

9. Explain what is short-circuiting and overloading in an electric supply.

10. What are magnetic field lines? How is the direction of a magnetic field at a point determined?

Mention two important properties of the

11.What are the factors which govern the force experienced by a current carrying conductor placed in

a

uniform magnetic field depends? ( 3 Marks )

12. Distinguish between an electric motor and generator?

13.What is direct current (d.c) and alternating current (a.c).

14.A current of 2 A flows through a circular coil of radius of 4 cm, and has 10 turns. The coil is

aligned horizontally and current flows though the coil in clockwise direction. Find the magnitude and

direction of magnetic field at the centre of the coil due to the current.

Five Mark Questions:

1. (a) Suggest an activity to show the pattern of magnetic field lines, when you are provided with a

bar magnet, a cardboard piece and iron filings.(b)Draw a rough sketch of the field lines which you

will observe.

2. (a) What is an electromagnet? What does it consists of? (b) Name one material in each case used to

make a (i) permanent magnet (ii) temporary magnet. (c) Describe an activity to show how can you

make an electromagnet in your school lab?

3. State Fleming’s left-hand rule. With a labeled diagram, describe the working of an electric motor.

What is the function of split-ring Commutator in a motor?

4. State Fleming’s right-hand rule. With a labeled diagram, describe the working of an AC electric

generator.

5. Draw the lines of force of the magnetic field through and around (a)single loop of wire carrying

current, (b) a solenoid carrying electric current.

6. Why is pure iron not used for making permanent magnets? Name one material used for making

permanent magnets. Describe how permanent magnets are made electrically. State two examples of

electrical appliances made by using permanent magnets.

7. (a)Draw a schematic labeled diagram of a domestic wiring circuit which includes (i)a main fuse (ii)

a power meter (iii)one light point (iv) a power plug.(b) Why is it necessary to connect an earth wire to

electric appliances having metallic covers?

8. (a)What are magnetic field lines? How is the direction of a magnetic field at a point determined?

(b) Draw two field lines around a bar magnet along its length on its two sides and mark the field

directions on them by arrow marks. (c) List any three properties of magnetic field lines.

9. What is an electric motor? With the help of a diagram, describe the working of an electric motor.

10. What are magnetic field lines? Write their characteristics. Draw the magnetic field lines due to a

current flowing in a circular coil.

11. Explain the principle, construction and working of an electric motor.

12. Explain with labeled diagram, the principle, construction and working of an electric generator.

13. (a ). What is an electromagnet ?

(b). List any of its two uses.

(c ). Draw a labeled diagram to show how an electromagnet is made.

(d ). What is the purpose of the soft iron core used in making an electromagnet ?

14.A solenoid is 1 m long and 2 cm in diameter has 50 turns/cm. A current of 5 A is flowing through

it. Calculate the magnetic induction:

a) Inside the solenoid.

b) At one end on the axis of solenoid.

15. Explain the construction and working of electric motor?

16. What is the principle behind the working of electric generator? Explain its working with the help


17. The mains power supply of a house is through a 5-A fuse. How many 100-W bulbs can be used in

this house at the correct voltage?

18. A wire 10 cm long and carrying a current of 1.5 A is held in a uniform magnetic field in which

B=10-3 T. Calculate the force on the wire if it is held perpendicular to the lines of the magnetic field.

19 A current of 10 A flows in a circular coil of 1000 turns and radius 0.1 m. Find the magnitude of

the magnetic field at the centre of the coil.

20. At what distance from a straight conductor carrying a current of 2.8 A, will the magnetic

induction be 2.8×10-5 T?

21. Find the strength of the current which will produce a magnetic field of 10-4 T at the centre of a

coil of mean radius 0.10 m. The coil comprises 20 turns.

22. A 0.4 m wire, stretched horizontally, carries an electric current of 15 A from East to West, in a

magnetic field whose magnetic field intensity is 0.1 N/Am, directed vertically downwards. What is

(a) the magnitude of the magnetic deflecting force on the wire, and (b) its direction?

cbse ncert solution Magnetic Effects of Electric Current

1.Why does a compass needle get deflected when brought near a bar magnet?

A compass needle is a small bar magnet. When it is brought near a bar magnet, its magnetic field

lines interact with that of the bar magnet. Hence, a compass needle shows a deflection when brought

near the bar magnet.

2.List the properties of magnetic lines of force.

The properties of magnetic lines of force are as follows.

(a) Magnetic field lines emerge from the north pole.

(b) They merge at the south pole.

(c) The direction of field lines inside the magnet is from the south pole to the north pole.

(d) Magnetic lines do not intersect with each other.

3.Why don’t two magnetic lines of force intersect each other?

If two field lines of a magnet intersect, then at the point of intersection, the compass needle points in

two different directions. This is not possible. Hence, two field lines do not intersect each other.

4.State Fleming’s left-hand rule.

Fleming’s left hand rule states that if we arrange the thumb, the centre finger, and the forefinger of

the left hand at right angles to each other, then the thumb points towards the direction of the magnetic

force, the centre finger gives the direction of current, and the forefinger points in the direction of

magnetic field.

5. What is the principle of an electric motor?

The working principle of an electric motor is based on the magnetic effect of current. A current-

carrying loop experiences a force and rotates when placed in a magnetic field. The direction of

rotation of the loop is given by the Fleming’s left-hand rule.

6.What is the role of the split ring in an electric motor?

The split ring in the electric motor acts as a commutator. The commutator reverses the direction of

current flowing through the coil after each half rotation of the coil. Due to this reversal of the current,

the coil continues to rotate in the same direction.

7.Explain different ways to induce current in a coil.

The different ways to induce current in a coil are as follows:

(a) If a coil is moved rapidly between the two poles of a horse-shoe magnet, then an electric current is

induced in the coil.

(b) If a magnet is moved relative to a coil, then an electric current is induced in the coil.

8. What are the essential difference between an AC generator and a DC generator

The essential difference between an AC generator and a DC generator is that

(a) AC generator has an electromagnet while a DC generator has permanent magnet.

(b) DC generator will generate a higher voltage.

(c) AC generator will generate a higher voltage.

(d) An AC generator has two rings called slip rings. A DC generator has two half rings called

commutator. This is the main difference between both the types of generators.

(d) AC generator has slip rings while the DC generator has a commutator.

A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is

(i) pushed into the coil, (ii) withdrawn from inside the coil, (iii) held stationary inside the coil?

9. A current induces in a solenoid if a bar magnet is moved relative to it. This is the principle of

electromagnetic induction.

(i) When a bar magnet is pushed into a coil of insulated copper wire, a current is induced

momentarily in the coil. As a result, the needle of the galvanometer deflects momentarily in a

particular direction.

(ii) When the bar magnet is withdrawn from inside the coil of the insulated copper wire, a current is

again induced momentarily in the coil in the opposite direction. As a result, the needle of the

galvanometer deflects momentarily in the opposite direction.

(iii) When a bar magnet is held stationary inside the coil, no current will be induced in the coil.

Hence, galvanometer will show no deflection.

1o. If we place a compass needle near straight conductor carrying current

(a)What happens to the deflection of the compass needle if the direction of current is

reversed .

(b)What change will you notice in the compass needle if it is moved away from

conductor but the current through the conductor remains the same?

(a) Direction of deflection will reverse

(b) Deflection will decrease

(One Mark Question)

Q.1 Why does the bulk of iron fillings stick to the ends of a bar magnet and not at its

centre?

Ans. Because at the ends magnetic strength is maximum and at centres magnetic strength is

least.

Q.2 If the frequency of A.C. is 50 Hz. Then how many times it is changing its

direction in 1 second?

Ans- 100 Times.

Q.3 What is the pattern of the magnetic field lines around a straight conductor

carrying current?

Ans. Concentric circles

Q.4 If the current is flowing in the direction of advancemet of screw, then what is the

direction of magnetic field lines?

Ans.In the direction of rotation of screw.

Q.5 How can you say that the magnetic field is uniform inside the solenoid.

Ans. Because field lines are parallel inside the solenoid.

Q.6 Which property of a proton will change while it moves freely in a magnetic field?

Ans. Momentum or Velocity.

Q.7 According to Flemings right hand rule, which part of right hand indicate the

movement of conductor?

Ans. Thumb

Q.8 If the no. of turns of a circular current carrying coil are doubled, then how will

the magnetic field produced by it changes?

Ans. Doubled

Q.9 In which position the force on conductor is maximum when it is placed in

uniform magnetic field?

Ans. When conductor is Perpendicular to field

10 A current through a horizontal power line flows in north to south direction.What

is the direction of magnetic field (i)at a point directly below it and (ii)at a point

directly above it?

Ans. (i) West to East (ii) East to West

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