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1. Matter is made up of tiny particles called _________.2. At the center of the atom is the nucleus which is

made up of _________ and __________.3. Surrounding the nucleus are particles called

_____________.4. A proton has a __________ charge. 5. An electron has an equal __________ charge while a

neutron is ____________.

1. Electric charge is denoted by the symbol Q. 2. The unit of electric charge is the _________ , C.3. Charge on one electron = - 1.6 x 10-19 C4. Charge on one proton = 1.6 x 10-19 C

5. A body is:(a) _________, if it has equal numbers of positive and

negative charges.(b) charged _________, if it has more negative than positive charges. (atom gains

electron)(c) charged _________, if it has more positive than negative charges. (atom losses

electron)

6. The force acting on two bodies of the same net charges will ______ each other.7. The force acting on two bodies of different net charges will ________ each other.8. The force causes movement of electrons or flow of charges.

Notes: If one coulomb of charge flows past in one second, then the current is ____ ampere. 15 amperes means in ______ second, ______ coulomb of charge flow through a cross

section of a conductor. In a metal wire, the charges are carried by ____________ Each electron carries a charge of ______________ C. 1 C of charge has _____________ electrons. Show your work.

Electric current is defined as the rate of flow of electric charge. Current, I = charge, Q Time, t The SI unit = ampere, A = C s-1

Define Electric Current

State the relationship between electron and electric current

Unit of electric charge

Where does charge come from?

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Activity 1: To investigate the relationship between electric charges and electric current.

Apparatus :Van de Graaff generator, connection wires, microammeter

Procedure 1. Start the motor of a Van de Graaff generator for a

few minutes to produce positive charges on the metal dome of the generator.

2. Bring your finger close to the dome of the generator. Observe what happens.

3. Touch the dome of the generator with the free end of the wire that is connected to the microammeter. Observe the microammeter needle closely.

4. Switch off the motor of the Van de Graaff generator.

Observation1. You will feel a brief _________ shock when your finger is brought close to the dome of the

generator.2. The microammeter needle is __________ when a wire is connected to the dome of the

generator.3. You can safely touch the metal dome with your finger.4. The microammeter needle is returned to its _________ position when the Van de Graaff is

switched off.

Explanation1. When the motor of the Van de Graaff generator is switched on, it drives the rubber belt. This

cause the rubber belt to rub against the roller and hence becomes _______ charged. The charge is then carried by the moving belt up to the metal _______ where it is collected. A large amount of _________ charge is built up on the dome.

2. The electric field around the metal dome of the generator can produced a strong force of ___________ between the opposite charges. ___________ will suddenly accelerate from the finger to the dome of the generator and causes a spark.

3. When the wire touches the dome, the microammeter needle is deflected. This shows that a __________ is flowing through the galvanometer.

4. The electric current is produced by the flow of ____________ from earth through the galvanometer to the metal dome to neutralize the positive charges on its surface.

5. The metal dome can be safely touched with the finger as all the positive charges on it have been ________________.

Conclusion A flow of electric charge (electrons) through a conductor produces an __________ _____

Predict what will happen if hair of a student is brought near to the charged dome. Give reasons for your answer.

The metal dome _________ the hair and the hair stand ____________

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This is because of each strand of hair receives __________ charges and __________ each other.

1. An electric field is represented by a series of arrowed lines called electric field line.

2. The lines indicate both the magnitude and direction of the field.3. The direction of an electric field is from a positively-charged object to a

negatively-charged object, from a positively-charged object to infinity, or from infinity to a negatively-charged object.

4. Electric field lines never cross each other.5. Electric field lines are closer in a strong electric field.

Activity 2 : To map the electric field around metal electrodes

Apparatus : Extra high tension (EHT) source, metal electrodes, petri dish, semolina grains, castor oil

Procedure:1. Two plane electrodes connected to the terminals

of an EHT power supply are dipped into a dish of castor oil.

2. The EHT is switched on and some semolina grains is sprinkled on the surface of the oil.

3. The electric field pattern formed by the semolina particles is observed and noted.

Sketch electric field lines showing the direction of the field

Define an electric filed.

An electric field is a region in which an electric charge experiences an electric force (attraction or repulsion).

An electric field is created from a positively charged sphere in the spaces surrounding it.

A negative charged body when placed at any point in this region is pulled towards the charged sphere – attractive force

A positively charged body that is placed in the same region is pushed away – repulsive force.

How does an electric field is repre-sented?

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4. The experiment is repeated using a plane electrode and a cylindrical electrode followed by two cylindrical electrodes.

Result: Sketch the electric field lines

Discussion1. Describe the direction of the electric field lines in the experiment?

________________________________________________________________________2. How is the strength of an electric field indicated with field lines?

_______________________________________________________________________

Conclusion

1. Electric field is ____________________________________________________________2. Like charges ________ each other but opposite charges __________ each other.3. An electric field can be represented by a number of lines called __________ ________

________ of force. 4. The lines indicate both the __________ and __________ of the field.5. The direction of the field lines is from _________ to ___________.

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Activity 3 To describe the effect of an electric field on a charge

I. A charged ball in an electric field

Switch on the EHT power supply and charge the ping-pong ball by contact with one of the electrodes. Observe what happen to the movement of the ping pong ball.

Observation & Discussion

1. When the EHT power supply is switched on, plate X is _________ charged and plate Y is _________ charged. Since the ping-pong ball is _________, it remains at the centre as the electric forces acting on it are ____________.

2. When the ping-pong ball touches the positively charged plate X, the ball receives __________ charges from the plate and experiences a __________ force. The ball will then ___________ to the negatively charged plate Y.

3. When the ball touches plate Y, the positive charges are ____________ by the negative charges. The ball then receives __________ charged and repels toward plate X. The process is repeated and the ball __________ to and fro between the two metal plates X and Y.

4. The rate of oscillation of the ping-pong ball can be increased by ___________ the voltage of the EHT power supply and ___________ the distance between the two plates X and Y.

II. The effect of an Electric field on a Candle Flame

The ping-pong ball is replaced with a candle.

The shape of the candle flame is observed.

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Observation

When the EHT power supply is switched on, the candle flame ___________ into two portions in opposite directions.

The portion that is attracted to the negative plate P is very much _________ than the portion that is attracted to the positive plate Q.

Switched off switched on

Explain the observation The hot flame of the candle ____________ the air molecules in its surrounding into positive

and negative ions. The ___________ ions are attracted towards the negative plate P. At the same time, the

negative ions are attracted to the positive plate Q. The movement of the ions towards the plated P and Q caused the candle flame to spread out.

Explain why the flame is not symmetrical The bigger portion of the flame is attracted towards the negative plate as the _______ of the

positive ions is larger than of the negative ions.

Solving problems involving electric charge and current

Example 1The current flows in a light bulb is 0.5 A.(b) Calculate the amount of electric charge that flows through the bulb in 2 hours.If one electron carries a charge of 1.6 x 10-19 C, find the number of electrons transferred through the bulb in 2 hours.

Example 2Electric charges flow through a light bulb at the rate of 20 C every 50 seconds. What is the electric current shown on the ammeter?

Example 3When lightning strikes between two charged clouds, an electric current of 400 A flows for 0.05 s. What is the quantity of charge transferred?

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TUTORIAL 7.1

1. Which of the following diagrams shows the correct electric field? (2003)

2. When the switch is on, the current that flows in an electronic advertisement board is 3.0 x 10-5 A. What is number of electrons flowing in the advertisement board when it is switched on for 2 hours? [charge of electron = 1.6 x 10-19 C] (2004)A. 3.84 x 1011

B. 1.67 x 1014

C. 1.35 x 1018

D. 4.17 x 1023

E. 1.50 x 1027

3. The following statements about the electric current are true exceptA. an electric current is a flow of electric

charge.B. The flow of current through a

conductor is directly proportional to the potential difference across the conductor.

C. Heat and magnetism are effects of the flow of a current

D. An electric current can be produced only by the flow of electrons.

4. An electric appliance has been switched on for 2 hours. Calculate the quantity of electric charge passing through the circuit in this time if the current is 2 A. (2007)A. 4 CB. 120 CC. 240 CD. 14 400 C

5. Figure 1 shows a candle flame split into two directions when it is placed in the space between two charged metal plates P and Q.

Which statement below explains why the candle flame has a greater tendency to spread towards plate Q than towards plate P?A. The electric field closer to plate Q is

stronger.B. Negative ions move faster towards

plate Q.C. Positive ions are heavier and move

slower towards plate Q.D. The candle flame is attracted by a

stronger magnetic force towards plate Q

6. Figure 2 shows a light sphere S, which is charged and suspended by a light nylon string between two charged plated P and Q.

Which statement about the arrangement shown is not true?A. Sphere S is negatively chargedB. Sphere S is attracted by an electric

force towards plate P.

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C. The angle of deflection will decrease if the separation between plates P and Q is increased.

7. (a) Plate P is connected to the positive terminal of an EHT power supply, while plate Q is connected to its negative terminal. A ping-pong ball coated with conducting paint is suspended between the two plates as shown figure below.

(i) What will happen to the ping-pong ball when the EHT is turned on?

(ii) Explain the reason for your answer in (a).

(iii) State two ways to increase the velocity of the oscillating ball.

(iv) Why we use the nylon thread?

(b)The ping-pong ball is replaced with a lighted candle.

(ii) In figure below, draw the shape of the flame when the EHT power supply is turned on.

(iii) Explain what causes the shape of the flame you have drawn in (b)(i)

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