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Science questions, chapter 6
Nama / NameKelas / ClassTarikh / Date

Electricity and magnetism

43 marks. Use Practice to check each answer as you go, or Exam to answer everything against the clock first.

Section A: objective questions

12 marks
Choose the best answer for each question.
1

Question 1

Which of the following is a renewable energy source?
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B
Biomass is a renewable energy source: it can be replaced continually. Natural gas, coal and nuclear energy are non-renewable.
For the teacher: Remembering, low difficulty, standard 6.1.1
Textbook p. 162
2

Question 2

When is an induced current produced in a coil of wire?
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A
An induced current is produced when magnetic field lines are cut, by moving the coil or the magnet. If both are stationary no field lines are cut.
For the teacher: Remembering, low difficulty, standard 6.1.2
Textbook p. 164
3

Question 3

Which row shows the energy changes in a hydroelectric power station?
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C
Water stored at a high level has gravitational potential energy. As it flows down it has kinetic energy, which turns the turbine and generator to give electrical energy. Option A is a thermal station.
For the teacher: Understanding, low difficulty, standard 6.1.2
Textbook p. 168
4

Question 4

Which of the following works with alternating current?
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D
A hair dryer is connected to the mains, which is alternating current. The calculator, torchlight and toy car use direct current.
For the teacher: Remembering, low difficulty, standard 6.1.3
Textbook p. 171
5

Question 5

Diagram 1 shows the trace on a C.R.O. screen when a supply is connected to the Y-input with the time-base on. The Y-gain is 5 V per division. What is the type of current and its greatest voltage?
C.R.O. screen with a wave-shaped trace that rises 2 divisions above and falls 2 divisions below the centre line
Diagram 1
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D
A wave that goes above and below zero shows alternating current. The greatest displacement is 2 divisions, so voltage = 2 × 5 = 10 V.
For the teacher: Applying, medium difficulty, standard 6.1.3
Textbook p. 173
6

Question 6

A transformer has 50 turns in its primary coil and 500 turns in its secondary coil. Which statement is correct?
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C
Fewer turns in the primary coil than in the secondary coil means a step-up transformer, so Vs is higher than Vp. Transformers work with alternating current only.
For the teacher: Understanding, low difficulty, standard 6.2.1
Textbook p. 178
7

Question 7

Diagram 2 shows a transformer. What is the secondary voltage Vs?
Transformer with a 240 V a.c. supply, primary coil of 1200 turns, secondary coil of 60 turns and a bulb
Diagram 2
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A
Vp/Vs = Np/Ns, so 240/Vs = 1200/60 = 20. Vs = 240 ÷ 20 = 12 V.
For the teacher: Applying, medium difficulty, standard 6.2.3
Textbook p. 182
8

Question 8

Why is a laminated iron core used in a transformer?
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D
The layers of soft iron separated by insulators reduce the eddy current that forms in the core, which makes the transformer more efficient.
For the teacher: Understanding, low difficulty, standard 6.2.2
Textbook p. 180
9

Question 9

Which component in the transmission system lets a power station or grid be closed for maintenance without disrupting the supply to consumers?
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B
The switch zone at the main substation sends electricity to the branch substation when needed and allows specific power stations and grids to be closed for maintenance.
For the teacher: Understanding, low difficulty, standard 6.3.1
Textbook p. 185
10

Question 10

Which colour is the earth wire in a 3-pin plug?
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C
Live wire is brown, neutral wire is blue and the earth wire has green and yellow stripes (international colour code).
For the teacher: Remembering, low difficulty, standard 6.3.2
Textbook p. 190
11

Question 11

An electric appliance is rated 1.5 kW, 240 V. Which fuse is most suitable for it?
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B
I = P ÷ V = 1 500 ÷ 240 = 6.25 A. The fuse value must be slightly higher than this, so the smallest value above 6.25 A is 10 A. A 5 A fuse would melt; 13 A and 30 A are larger than needed and give less protection.
For the teacher: Applying, medium difficulty, standard 6.3.3
Textbook p. 192
12

Question 12

A 2 kW heater is used for 3 hours. The cost of electricity is 20 sen per unit. What is the cost?
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A
Energy = 2 kW × 3 h = 6 kWh (6 units). Cost = 6 × 20 sen = 120 sen = RM1.20.
For the teacher: Applying, low difficulty, standard 6.4.4
Textbook p. 200

Section B: structured questions

31 marks
Answer all questions.
13

Question 13

Diagram 3 shows three arrangements, X, Y and Z, of a magnet and a coil of wire connected to an LED.
Arrangement X: magnet moves towards a stationary coil. Arrangement Y: magnet and coil both at rest. Arrangement Z: coil moves away from a stationary magnet.
Diagram 3
[2 marks] (a)State the arrangements in which the LED lights up.
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[1 mark] (b)Explain why the LED does not light up in arrangement Y.
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[1 mark] (c)Name the device in a power station that uses the same principle.
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For the teacher: Understanding, low difficulty, standard 6.1.2
Textbook p. 164
14

Question 14

Diagrams 4(a) and 4(b) show the traces on a C.R.O. screen when two different supplies are connected to the Y-input in turn, with the time-base on. In Diagram 4(a) the Y-gain is 0.5 V per division.
C.R.O. screen with a straight horizontal line 3 divisions above the centre line
Diagram 4(a)
C.R.O. screen with a wave-shaped trace
Diagram 4(b)
[2 marks] (a)Name the type of current shown in (i) Diagram 4(a) and (ii) Diagram 4(b).
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[2 marks] (b)Calculate the voltage of the supply in Diagram 4(a).
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[1 mark] (c)The terminals of the supply in Diagram 4(a) are reversed. State the change in the trace.
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For the teacher: Analysing, medium difficulty, standard 6.1.3
Textbook p. 172
15

Question 15

Diagram 5 shows a transformer used to light a 12 V bulb from the 240 V mains. The primary coil has 1 000 turns.
Transformer with a 240 V a.c. supply, 1000 primary turns, unknown secondary turns and a 12 V bulb
Diagram 5
[2 marks] (a)Is this a step-up or a step-down transformer? Explain your answer.
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[2 marks] (b)Calculate the number of turns of the secondary coil, Ns.
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[1 mark] (c)Why does this transformer not work if it is connected to a battery?
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For the teacher: Applying, low difficulty, standard 6.2.3
Textbook p. 182
16

Question 16

Diagram 6 is a flow chart of the transmission and distribution of electricity. Boxes P, Q and R are not labelled.
Flow chart: power station at 11 kV or 25 kV, box P, National Grid Network, main substation, box Q, box R
Diagram 6
[1 mark] (a)Name the component P.
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[1 mark] (b)Name the component Q, which sends electricity to the branch substation when needed.
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[1 mark] (c)Name the component R, which reduces the voltage for consumers.
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[1 mark] (d)What is the voltage of the alternating current supplied to homes in Malaysia?
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For the teacher: Remembering, low difficulty, standard 6.3.1
Textbook p. 184
17

Question 17

An electric kettle is rated 2.4 kW, 240 V and has a 3-pin plug with a fuse.
[2 marks] (a)Calculate the current that flows through the kettle.
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[1 mark] (b)Which fuse is most suitable for the plug?
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13 A
The fuse value should be slightly higher than the normal current of 10 A. A 5 A fuse would melt at once, and a 10 A fuse has no margin above the normal current.
[2 marks] (c)The metal casing of the kettle is connected to the earth wire. Explain how this protects a person if the live wire touches the casing.
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For the teacher: Applying, medium difficulty, standard 6.3.3
Textbook p. 192
18

Question 18

The table shows the energy for two lamps. Lamp X is a filament lamp and lamp Y is an LED lamp.
LampElectrical energy supplied (J)Light energy produced (J)
X20018
Y200180
[2 marks] (a)Calculate the energy efficiency of lamp X.
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[1 mark] (b)Which lamp is more energy efficient? Give a reason.
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[2 marks] (c)Lamp Y is rated 10 W and is used for 5 hours every day for 30 days. Calculate the cost if the rate is 30 sen per unit.
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For the teacher: Evaluating, high difficulty, standard 6.4.1
Textbook p. 195
19

Question 19

Hana wants to find out how the number of turns of the secondary coil of a transformer affects the brightness of a bulb. She winds a primary coil of 30 turns on a laminated iron core, connects it to an a.c. supply and changes the secondary coil from 15 turns to 60 turns.
[1 mark] (a)State the manipulated variable.
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[1 mark] (b)State the responding variable.
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[1 mark] (c)Write a hypothesis for this investigation.
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For the teacher: Creating, high difficulty, standard 6.2.1
Textbook p. 178