Static electricity1. Static electricity is electrical charge that is at rest or not moving.2. The study of static electricity is called electrostatics.3. There are two types of static electric charge, i.e. positive charges and negative

charges.4. Positive charges consist of protons. Protons cannot move.5. Negative charges consist of electrons. Electron transfer happens when two

different materials are rubbed together.Characteristics of static electric charges

1. Positive charges and negative charges have the ability to attract or repel other charges.

2. Charges of the same type (like charges) repel one another.

3. Charges of different types (unlike charges) attract one another.

4. The repulsive force and attractive force that exist between electrical charges is called electrostatic force.

5. Electrostatic force is a type of force caused by static electric charges.

6. Electrostatic force on a charged object causes an object without charge to be attracted to it.

Production of static electric charges

1. Static electric charges can be produced on a neutral object by rubbing it with a different material like a woollen or silk cloth.

2. When two different materials are rubbed, electron transfer occurs. One of the material receives electrons while the other loses electrons.

3. The material that receives electrons becomes negatively charged because it has more electrons than protons.

4. The material that loses electrons becomes positively charged because it has more protons than electrons.

5. An object is neutral if the number of positive charges (protons) and negative charges (electrons) is the same.

6. Examples of materials that are easily charged are cellulose acetate and polythene.

7. The type of charge produced depends on the types of material that are rubbed together.

Detection of electric charges

1. An electroscope is used to detect snail electric charges or static eiectric charges.2. Charged materials can also be detected by an electroscope.

3. Before it is used, the electroscope should be earthed by touching the metal disc with a finger. This is intended to neutralise the electroscope.

4. When a charged material is brought near the metal disc of the electroscope, its gold foil will diverge.

5. When a material that is not charged (neutral) is brought near the metal disc of the electroscope, its gold foil does not diverge.

Phenomenon related to static electric charges in d •Friction between two materials produces electric charges. Because of this. electric charges can be produced anywhere.

(a) Occurrence of lightning· Clouds acquire electrical charges when water vapour in it rubs with air.

(b) Spark plug· A spray of sparks is produced when a car enaine is started.· Electric charges 'jump' across spark space on the plug to produce sparks.· These sparks cause fuel to burn to produce energy.

(c) Nylon clothes

· A crackling sound is heard when we take off our nylon clothes on a dry day.· This is because static electric charges are produced when the nylon clothes rub against

our body.(d) Combing hair

· Dry hair will stand erect or will be attracted towards the comb on a dry day.· This is because hair becomes charged when it rubs against the comb.

(e) Electronic lighter· Electric charges are produced when an electronic lighter is lit produce sparks.· The sparks will then ignite the gas.

Safety measures related to static electric chargesSafety measures should be taken in certain Re1ations related to static electric charges.a Lightning conductor

· The roofs of high buildings are usually installed with lightning conductors to protect these buildings from being struck by lightning.

· The end of a lightning conductor that is branched and sharp directs the electric charges of the lightning to the earth (earthed).

· The other end of the lightning conductor is buried in the ground to direct the electric charges from the lightning to the earth without damaging the building.Oil tanker

· An oil tanker becomes charged with static electricity when it moves because of friction with air.

· Furthermore, the rubber tyres prevent the charges from flowing to the earth.· Because of this, a metal chain is fixed to the bottom of the tanker to direct the charges to

the earth when the metal chain touches the road.

· This is important as it prevents sparks from being produced that may cause a fire.Aeroplane

· An aeroplane will acquire high electric charges when it rubs against the air as it flies.· Aeroplane tyres are specially made to direct electric charges to the earth when the plane

lands.ELECTRICITY- Sources of electrical energy

1. Electrical energy is energy produced when electric current flows.2. A source of electrical energy is any device that produces electric charges or

electric current.3. Dry cells are a type of chemical cells most widely used in electrical appliances

like radios, torchlights and clocks. A new dry cell supplies 1.5 V voltage.4. An accumulator is the battery used in vehicles like cars, lorries, motorcycles, vans

and buses. An accumulator is used to start the engine of vehicles and light the vehicle lights.

5. A dynamo is found on a bicycle and produces electrical energy when the bicycle is pedalled.

Electric current

1. Moving electric charges (electrons) produce electric current.2. Electric current enables electrical appliances like televisions, refrigerators and

fans to operate.3. Electric current is produced when electrons flow in a certain direction.

4. The Van de Graaff generator is a device that can produce electric charges (electrostatic charges) of very high voltage on its dome.

· When the genarator is turned on, the rubber belt turns and rubs against both rollers. The dome becomes charged.

· The genarator dome is usually positively charged (the generator dome can be positively or negatively charged).

· A dry dome can hold its charges longer.

Voltage1. Voltage is electrical energy that is needed to enable electrons to flow from one

point to another in a conductor.2. Voltage is the force that pushes electrons through a circuit to produce electric

current.3. A dry cell or battery possesses voltage.

Resistance1. Electrons that flow through a conductor constantly experience obstruction.2. The characteristic of a material that opposes the flow of electrons called resistance.3. A material with high resistance allows only a small current to pass through it.4. Resistance in a conductor, for example a wire, depends on

(a) length of conductor· The longer the conductor, the higher its resistance.

(b) diameter or thickness of conductor· The bigger the diameter of the conductor, the lower its resistance.

c) type of conductor· Different types of conductor have different resistance.· Copper and aluminium which are widely used as electric wires are a few metals that have

low resistance.5. Some conductors have high resistance to current that flows through them. This type

of conductor is called a resistor. Direction of electron flow and current in an electric circuit1. In a dry cell, current is produced when electrons flow from the negative terminal of

the cell to the positive terminal through a wire.2. However, the direction of current flow is the opposite of the direction of electron

flow.3. Electric current flows from the positive terminal to the negative terminal of a cell.

MEASURING ELECTRICITY

Measuring electric current1. Electric current that flows from a source of electrical energy can be measured with

an ammeter.2. The unit of measurement for current is ampere (A)3. The ammeter is connected in series to a circuit when measuring current.

4. If the ammeter needle does not move, this shows that no current is flowing in the circuit.

5. The positive terminal of the ammeter should be connected to the positive terminal of the electric source in an electric circuit. Similarly, the negative terminal of the ammeter should be connected to the negative terminal of the electric source.

Measuring voltage1. Voltage can be measured with a voltmeter.2. The unit of measurement for voltage is volt (V).3. The voltmeter is connected in parallel to a circuit when measuring voltage.4. The positive terminal of the voltmeter should be connected to the positive

terminal of the electric source in an electric circuit.Measuring resistance

1. Resistance is measured in the unit of ohm.2. The symbol of ohm is E2.3. A resistor is a device that is used to reduce the electric current that flows in a

circuit.4. The bigger the ohm value in a resistor, the bigger is its resistance.

RELATIONSHIP BETWEEN ELECTRIC CURRENT, VOLTAGE AND RESISTANCERelationship between resistance and electric current1. The quantity of electric current that flows through a circuit will change according to

the resistance.2. The bigger the resistance, the smaller the electric current that flows through a circuit.3. If the resistance is small, the quantity of electric current that flows through a circuit

will be big. Relationship between voltage and electric current

1. The quantity of electric current that flows through a circuit will change according to the voltage.

2. The higher the voltage, the greater the electric current that flows through the circuit.3. When the voltage of an electric source increases, the electric current that flows

through the circuit will also increase.Relationship between voltage, electric current and resistance

1. The electric current that flows increases at the same rate as the rate of increase in voltage value.

2. The voltage quantity is directly proportional to the quantity of electric current.

3. The relationship between voltage, electric current and resistance,

is called Ohm's Law.

4. R is constant for a fixed resistor. Therefore, the ratio of voltage to VI

electric current,

is always fixed. This fixed value is called resistance.5. If a voltage (V) versus electric current (A) graph is drawn, a straight line that passes

through the origin is obtained. The gradient of the graph represents the circuit resistance.

6. Ohm's Law is used to solve problems related to values of voltage, electric current and resistance.

7. If any two values in the formula R = —I are known, the third value can be determined.

8. The following steps are a guide to solving problems related to Ohm's Law.

PARALLEL AND SERIES CIRCUITSSymbols of electric circuit componentsTo make the drawing of an electric circuit easier, components of an electric circuit should be represented by certain symbols.

Electric circuit1. An electric circuit is a path that allows electric current to flow through it.2. An electric circuit must be properly and completely arranged so that electric current

can flow through it.3. The bulb will light up or the ammeter needle will deflect if an electric circuit is

connected correctly.

4. There are two types of electric circuit, i.e.(a) series circuit(b) parallel circuit

Series circuit

1. When circuit components like a bulb or resistor is connected from end to end or in a row, the circuit is called a series circuit.

2. The electric current flows on only one path from the positive terminal to the negative terminal of an electric source.

3. In a series circuit, if one part of the circuit is disconnected or the bulb is burnt, the circuit becomes incomplete and other bulbs will also be put out.

Parallel circuit

1. In a parallel circuit, electric components are arranged side by side and parallel to one another.

2. There is more than one path for the flow of electric current.3. In a parallel circuit, if one bulb or resistor is spoilt or removed, electric current will

still flow through another path. Other bulbs are still lit.

ELECTRIC CURRENT, VOLTAGE AND RESISTANCE IN A SERIES CIRCUITFlow of electric current in a series circuit

1. The ammeter gives the same reading even though it is connected at different positions. This shows that the current that flows in all the positions in a series circuit is the same.

2. If the current that flows through the ammeter X, Y dan Z are represented respectively by symbols I, I1, and I2 then the ampere values for I, I1 and I3 are the same, i.e.: I=I1=I2

Voltage in a series circuitVoltage of cells in series

1. The more cells that are connected in series, the greater the current that flows. This is because more cells supply greater voltage or electrical energy to the circuit.

2. The more cells connected in series, the bigger the total cell voltage. This causes the bulb to shine brighter.

3. The total voltage is the same as the sum of the voltages of each cell.

age of bulbs in series1. The voltage that passes through every circuit component like the bulb (or resistor) in

a series circuit is the same.2. The voltage that passes through all the circuit components t supplied by an electric

source) is the same as the total voltage of each circuit component.

3. If the voltage that is supplied by an electric source is represented by the symbol V and bulb X and Y respectively use voltage value V1 and V2, then the relationship between V, V1 and V2 is

Resistance in a series circuit1. If more bulbs are added in series, resistance in the circuit will increase causing the

current that flows through the bulbs to decrease. Therefore, the bulbs will shine dimly.

2. If resistance of the bulbs are represented by R1 and R2, resistance (R) in a series circuit is the sum of the resistance in each bulb, i.e.:

3. In a series circuit,(a)the current that flows through each bulb is the same.

(b)the voltage supplied by the electric source is shared by all the bulbs. The voltage that passes through the circuit is the same as the sum of the voltage used by each bulb.

(c) the circuit resistance is the sum of the resistance in each bulb.

4. The following steps are used to solve problems related to voltage, electric current and resistance in a series circuit by using Ohm's Law.

Advantages and disadvantages of a series circuit

ELECTRIC CURRENT, VOLTAGE AND RESISTANCE IN A PARALLEL CIRCUITFlow of electric current in a parallel circuit

1. In a parallel circuit, the quantity of current supplied by the electric source will be channelled to the branches according to their resistance value.

2. If a circuit branch has high resistance, the current value that flows through it will be low and conversely, if the circuit branch has low resistance, the current value that flows through it will be high.

3. The quantity of current supplied by the electric source in a parallel circuit is the same as the sum of the current that flows through each branch path.

(a) Bulbs in each circuit branch with the same resistance will shine with the same brightness because electric current with the same value will flow through both bulbs at the same time.

(b) The current at position P is the same as the sum of the current at positions Q and R.(c) If the current flowing through ammeter P, Q and R is represented by symbols I, I1 and I2

respectively, then the ampere value relationship of I, I1 and I2 is as follows. I = I1 + I2

Voltage in a parallel circuitVoltage of cells in parallel

1. Voltage does not increase or decrease if cells of the same type are connected in parallel.

2. Compared to cells in series, cells in parallel are more lasting. The more cells there are in a parallel arrangement, the more lasting they are as electrical energy suppliers.

Voltage of bulbs in parallel1. The value of the voltage across each bulb or resistor is the same.2. The voltage value is the same although the resistance value in each branch is

different.3. The voltage across each bulb is the same as the voltage supplied by the electric

source.

4. If the voltage recorded by the voltmeter at positions P, Q and R in Figure 7.40 are represented by symbols V, V1 and V2 respectively,

then the voltage value relationship of V, V1 and V2 is as follows.

Resistance in a parallel circuit1. If R is the total resistance and the resistance of the resistors in Figure 7.41 is

represented by R1 and R2 respectively, then the relationship between R, R, and R, in the parallel circuit is

2. In a parallel circuit,(a)the quantity of current supplied by the electric source is the same as the sum of the

electric current that flows through each circuit branch.

(b)the voltage across each bulb is the same as the voltage supplied by the electric source.

(c)the total circuit resistance is represented by the following formula.

3. The following steps are used to solve problems related to voltage, electric current and resistance in a parallel circuit by using Ohm's Law.

Advantages and disadvantages of a parallel drat*

MAGNETISM1. A magnet has two poles, i.e. north pole and south pole, that are situated at each

end of the magnet.2. Like magnetic poles repel one another while unlike magnetic poles attract one

another.

3. A magnet can only attract materials that are made of iron, nickel and cobalt.4. Materials that are attracted by magnet are called magnetic materials. Examples of

such materials are iron nails, paper clips, one sen coins, shaving blades and needles.

5. Materials that are not attracted by magnet are called nonmagnetic materials. Examples of non-magnetic materials are glass, plastic, paper, magnesium tape, zinc foil and wood.

Magnetic field1. A magnet has a magnetic field around it.2. A magnetic field is the space around a magnet that gives the magnetic effect.3. A magnetic field is strongest at the two poles of a magnet. This can be seen if iron

filings are scattered on top of a magnet. Most of the iron filings are attracted to the two magnetic poles.

4. A magnetic field consists of magnetic lines of force.5. Magnetic lines of force do not meet, do not cut or cross one another.6. A magnetic field cannot be seen or felt. Its pattern can be seen by scattering iron

filings on it. The iron filings form the magnetic lines of force.7. All magnetic lines of force have direction, i.e. point from the north pole to the

south pole.

8. The direction of magnetic lines of force can be determined by using a compass.9. A magnetic field can deflect the compass needle. The direction of the deflected

compass needle always follows the direction of the magnetic lines of force.10. A strong magnet has magnetic lines of force that are closer together.

11. From Figure 7.48, it can be seen that(a) all magnetic lines of force do not cross one another.(b) all magnetic lines of force point from the north pole to the south pole.(c) magnetic lines of force join it the poles are different. This shows that unlike magnetic

poles attract one another.(d) magnetic lines of force do not join if the poles are similar. This shows that like magnetic

poles repel one another.(e) in arrangements (b), (c) and (d), there are areas called neutral points (X). The neutral

point in a magnetic field is the area where(i) magnetic effect is not felt.(ii) there are no magnetic lines of force.(iii) there is no influence on a compass needle. Use of a magnet in a compass

1. A magnet is used in a compass to determine direction.2. A magnet that is suspended freely will eventually stop moving and point to the

north-south direction. This principle is used in a compass.3. A compass needle will always point to the north pole of the Earth.

ELECTROMAGNETISMFlow of electric current through a straight conductor

1. The electric current that flows through a straight conductor will produce a magnetic field around that conductor.

2. The magnetic field that is produced around a straight conductor that carries a current is circular in shape.

3. The direction of the magnetic field that is produced around a straight conductor depends on the direction of the current.

Electromagnet

1. Electromagnetism is the study of the relationship between electricity and magnetism.

2. An electromagnet is a conductor that has characteristics similar to those of a magnet (e.g. it has magnetic force and two different magnetic poles) when an electric current flows through it.

3. An electromagnet consists of a solenoid (wire coil) that is wound around a soft iron core.

4. The soft iron core functions to strengthen the magnetism of the solenoid.5. Soft iron is used because it is easier to be magnetised and also easier to demagnetise

when electric current stops flowing through it.6. When electric current flows, the soft iron becomes a magnet. However, its

magnetism will disappear when the electric current is cut off.7. Just as a normal bar magnet, an electromagnet also has two different poles, i.e. the

north pole and south pole.8. The types of pole in an electromagnet depends on the direction of the electric

current that flows through it.

9. The strength of the magnetic field in an elecliomagnet can be varied.10. The strength of the magnetic field in an electromagnet can be increased by

(a) increasing the number of turns of the solenoid.(b) increasing the electric current that flows.(c) reducing the diameter of the solenoid.

11. Electromagnets are used in devices like telephones, electromagnetic cranes, telegraph machines, electric bells and car horns.

12. An example of the use of an electromagnet in daily life is the electric bell.(a) When the switch is turned on, electric current flows through the circuit.(b) The electromagnet in the bell attracts the armature and the hammer together causing the

hammer to hit the bell. Sound is produced.(c)At the same time, the circuit is broken at the contact point.(d)Electric current ceases to flow and the magnetism of the electromagnet disappears. The

armature is pulled back to its original position by a spring and touches the contact point once again.

(e)The electromagnet attracts the armature again and the hammer hits the bell again.(f) This process is repeated to produce the ringing sound in an electric bell.

1. Static electricity is electric charges that are at rest or not moving.2. There are two types of static electric charge, i.e. positive charges and negative

charges.3. Like charges repel one another while unlike charges attract one another.4. When two different materials are rubbed together, electron transfer occurs. One of

the materials receives electrons while the other material loses electrons.5. An electroscope is used to detect static electric charges.6. Lightning is an example of an electrostatic charge phenomenon that occurs in

daily life.7. Electric charges that move produce electric current.8. A Van de Graaff generator is a device that produces electric charges (electrostatic

charges) of high voltage.9. Voltage is electrical energy that is needed to enable electric charges (electrons) to

flow from one point to another in a conductor.10. The characteristic of a material that opposes the flow of these electric charges is

called resistance.11. Resistance in a conductor depends on the length of the wire, the thickness of the

wire and the type of wire.12. Electric current flows from the positive terminal of a cell to the negative terminal

of that cell. However, the direction of electric current flow is opposite to that of electron flow.

13. An ammeter is connected in series while a voltmeter is connected in parallel in a circuit.

14. Electric current is measured with an ammeter while voltage is measured with a voltmeter.

15. Current and voltage are measured in units of ampere (A) and volt (V) respectively.

16. The bigger the resistance, the smaller the electric current that flows in a circuit.17. The higher the voltage, the greater the electric current that flows in a circuit.

18. Ohm's Law, R = VI

, shows the relationship between voltage, current and

resistance.

19. An electric circuit is a path that allows electric current to flow through it.20. When a circuit component lika a bulb or resistor is connected from end to end or

in a row, the circuit is called a series circuit.21. If a bulb in a series circuit is burnt, the circuit becomes incomplete and the other

bulbs in the circuit will also not light up.22. In a parallel circuit, the electric components are arranged side by side and parallel

to one another.23. The electric current in all positions in a series circuit is the same.

24. The voltage across a circuit is the same as the sum of the volta! across each bulb in a series circuit.

25. The resistance in a series circuit is the sum of the resistance in each bulb.

26. The quantity of current supplied by an electric source in a parallel circuit is the same as the sum of the current that flows through each branch path.

27. Voltage does not increase or decrease if more cells of the same type are connected in parallel.

28. Resistance in a parallel circuit is represented by the following formula:

29. A magnetic field consists of magnetic lines of force.30. Magnetic lines of force do not cross one another.31. The direction of magnetic lines of force can be determined by using a compass.32. A magnet is used in a compass to determine direction.33. Electric current that flows through a straight conductor will produce a magnetic

field that is circular in shape around the conductor.34. An electromagnet is a conductor that has characteristics similar to that of a

magnet when electric current flows through it.35. An electromagnet consists of a solenoid (wire coil) that is wound around a soft

iron core.36. The magnetism of an electromagnet will disappear if the electric current that

flows through it is cut off.37. Electromagnets are used in devices like telephones and electromagnetic cranes.