Form 3 Chapter 7

Form 3 Science Chapter 7

FORM 3 CHAPTER 7 ELECTRICITY

1. Diagram 1 shows electrical circuits P and Q.

P: ………………………………………

Q: ………………………………………

Diagram 1

(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

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Q

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Form 3 Science Chapter 7

[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? R= Voltage Current

[2 marks]

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Form 3 Science Chapter 7

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

P

Q

R

S Diagram 2

(a)

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

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(b)

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

Common property

Examples

[4 marks]

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

Situation (a)

Torch light with two dry cells

Torch light with one dry cell Diagram 3.1

(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]

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(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.

Diagram 3.2 (i) Record the reading of the ammeter in Table 3.3 when different number of dry cells is used.

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1 dry cell

2 dry cells

3 dry cells

4 dry cells

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Form 3 Science Chapter 7

Number of dry cells One Two Three Four

Reading of the ammeter (A)

Table 3.3 [2 marks] 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.

Reading of ammeter (A)

(ii)

Number of dry cells

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[2 marks]

Form 3 Science Chapter 7

(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. ………………………………………………………………………………………………………. ………………………………………………………………………………… …………………… [1 mark]

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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.

Dry cell

Ammeter

A

Switch

Q

P cm copper wire Diagram 4.1

(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

5

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Value (A)

0.10

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10

……………………

15

……………………

20

………………….

25

…………………

Table 4.2

[2 marks]

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(c)

Using Table 4.2, draw a graph of current against diameter of copper wire.

1.0

0.8

Current (A)

0.6

0.4

0.2

5

15

10

Diameter of copper wire (mm)

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20

25

Form 3 Science Chapter 7

[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?

………………………………………………………………………………………………………

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……………………………………………………………………………………………………… [1 mark]

5. Diagram 5 shows an activity carried out to show the effect of electric current flowing through a straight wire. Straight wire Cardboard Compass Q P JPN Pahang 2009

188 Diagram 5

Form 3 Science Chapter 7

(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.

P

Q [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

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N

S

Diagram 189 6

Q

Form 3 Science Chapter 7

(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.

P

Q [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]

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