Form 3 Chapter 7

FORM 3 CHAPTER 7 ELECTRICITY

1.

Diagram 1 shows electrical circuits P and Q.

(a)

On Diagram 1, label P and Q using the following words

Parallel circuit Series circuit

[2 marks]

(b)

Draw a circuit diagram for P and Q using symbols to represent the various electrical

components.

P: ……… Q: ………

Diagram 1

[2 marks]

(c)

What will happen if

(i) one bulb in circuit P is faulty?

……….. [1 mark] (ii) one bulb in circuit Q is faulty?

……….. [1 mark]

(d)

In circuit P, if the current passing through one bulb is 2A and the voltage across

the bulb is 8V, what is the resistance of the bulb?

[2 marks] R= Voltage

2.

Diagram 2 shows electric circuits P, Q, R and S.

(a)

Based on your observations on Diagram 2, state how the bulbs are connected in each circuit. P: ……….. Q: ……….. R: ……….. S: ……… [4 marks] P _Q R S Diagram 2

(b)

Classify P, Q, R and S into two groups based on their common properties. Give examples for each group.

[4 marks] P, Q, R and S

Common property

3.

(a) Diagram 3.1 shows two torch lights powered by a dry cell and two dry cells are being switched on.

(i)

Based on the observations in Diagram 3.1, state the .difference in the brightness of the torch lights.

……… ……….. [1 mark]

(ii) State an inference based on the observation in Diagram 3.1.

……… ………

[1 mark] (iii) State one hypothesis that can be made based on the observation in Diagram 3.1.

………..……….. ………..…..

[1 mark] Diagram 3.1

Torch light with one dry cell Situation (a)

Torch light with two dry cells Situation (b)

(b)

A student carried out an experiment to investigate the situation in Diagram 3.1. Diagram 3.2 shows the experiment to determine the effects of changing the number of dry cells to current. The reading of the ammeter is recorded when different number of dry cells is used.

(i) Record the reading of the ammeter in Table 3.3 when different number of dry cells is used.

Diagram 3.2

1 dry cell 2 dry cells

Number of dry cells Reading of the ammeter (A) One Two Three Four Table 3.3 [2 marks]

(ii)

Based on the readings in Table 3.3, draw a line graph to show the relationship

between the number of dry cells and the reading of ammeter.

[2 marks] Number of dry cells

R

eadi

ng of

am

me

te

r

(A

)

(iii) State the variables involved in this experiment.

Manipulated variable: ………. Responding variable: ……….. Constant variable: ………

[3 marks] (c) Based on the experiment, state the operational definition of current.

……… …. ……….. [1 mark]

(d)

Suggest one way the student can increase the brightness of the bulb in Diagram 3.2

without increasing the number of dry cell.

………. ……… ………

4. Diagram 4.1 shows the schematic diagram for an experiment to study the relationship between the thickness of wire and the current flowing through the circuit. Five copper

wires with different diameters are attached to P and Q respectively and the reading of the ammeter is recorded.

(a)

State the variables involved in the experiment.

Manipulated variable: ………. Responding variable: ………. Fixed variable: ……….

[3 marks]

(b)

Record the ammeter reading in the space provided in Table 4.2

Diameter of copper wire (mm)

Reading of ammeter Value (A)

5 0.10

A

Dry cell Switch cm copper wire Ammeter P Q Diagram 4.1

10 ……… 15 _……… 20 ………. 25 ……… Table 4.2 [2 marks]

(c)

Using Table 4.2, draw a graph of current against diameter of copper wire. C urr en t ( A )

Diameter of copper wire (mm)

5 10 15 20

25

0.2 0.4 0.6 0.8 1.0

[2 marks] (d) Predict the reading of ammeter if the diameter of the copper wire is 23 mm

……… [1 mark]

(e) State the relationship between the diameter of copper wire and the current flowing through the circuit

……… [1 mark] (f) What happens to the resistance in the circuit if the diameter of the wire is increased?

……… [1 mark]

5. Diagram 5 shows an activity carried out to show the effect of electric current flowing through a straight wire.

Q

Cardboard Compass Straight wire

(a)

On Diagram 5, draw an arrow to show the direction of current flow.

[1 mark]

(b)

Plotting compasses are placed at position P and Q.

(i) Draw the direction of the compass needle in the diagram below.

[2 marks] (ii) Draw the pattern of the magnetic field formed around the wire.

[1 mark]

(c)

Give one example of the use of an electromagnet.

……… [1 mark]

6

. Diagram 6 shows the magnetic field formed around a bar magnet.

P Q

N S

(a)

Using à, draw the direction of the magnetic field lines in the box provided in Diagram 6. [1 mark] (b) P and Q are compasses placed around the bar magnet. Draw the direction of the

compass needle below.

[2 marks] (c) (i) Which part of the bar magnet has the strongest magnetic field?

……….. [1 mark] (ii) Give one reason for the answer in (c)(i).

……….. [1 mark] (d) State one property of the magnetic field lines.

………. [1 mark]