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Secondary 4 Pure Physics Preliminary Examination Paper 5

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Questions

TuitionGoWhere Exam Practice (AI) - Pure Physics Secondary 4 PRELIM (Version 5)

School: TuitionGoWhere Secondary School (AI)
Subject: Pure Physics
Level: Secondary 4
Paper: PRELIM Practice Paper (Version 5 of 5)
Duration: 75 minutes
Total Marks: 60
Name: ______________________
Class: ______________
Date: ______________

Instructions

Answer all questions in the spaces provided.
Show all working clearly where calculations are required.
Use SI units unless otherwise stated.
Section A: Structured Questions (1–8)
Section B: Calculation and Data Questions (9–14)
Section C: Conceptual and Applied Questions (15–20)

Section A: Structured Questions (16 marks)

1. [2 marks]
State the function of the neutral wire in a household alternating current (AC) circuit.

2. [1 mark]
State one advantage of using a circuit breaker rather than a fuse to protect an appliance.

3. [2 marks]
A positively charged plastic rod is brought near a coil connected to a galvanometer. The needle deflects to the right. State what is observed when the rod is removed quickly.

4. [2 marks]
The diagram below shows a simple transformer.

Image pending generation: diagram for 4.

State the relationship between the turns ratio and the voltage ratio for an ideal transformer.

5. [2 marks]
Explain why the efficiency of a real transformer is always less than 100%.

6. [2 marks]
A wire carrying current is placed between the poles of a magnet as shown.

Image pending generation: diagram for 6.

Using Fleming’s left-hand rule, state the direction of the force acting on the wire.

7. [2 marks]
State two ways to increase the magnitude of the induced electromotive force (e.m.f.) in a coil by electromagnetic induction.

8. [3 marks]
The earth wire in a household appliance is normally not carrying current. Explain its purpose and state what happens to it during a fault.

Section B: Calculation and Data Questions (24 marks)

9. [2 marks]
A transformer has a primary voltage of 240 V and a secondary voltage of 12 V. The primary coil has 600 turns. Calculate the number of turns in the secondary coil.

Working:

Answer: ________ turns

10. [2 marks]
An ideal transformer has 1200 turns on the primary and 300 turns on the secondary. If the primary current is 0.50 A, calculate the secondary current.

Working:

Answer: ________ A

11. [3 marks]
A transformer is 80% efficient. The secondary coil delivers 9.0 V at 2.0 A. The primary voltage is 230 V. Calculate the current in the primary coil.

Working:

Answer: ________ A

12. [3 marks]
A coil of wire is moved quickly into a magnetic field. The magnetic flux changes by 0.040 Wb in 0.020 s. The coil has 50 turns. Calculate the magnitude of the induced e.m.f.

Working:

Answer: ________ V

13. [4 marks]
The graph below shows the output voltage of a generator over time.

Image pending generation: graph for 13.

(a) Determine the frequency of the output. [2]
(b) State the type of current produced. [1]
(c) Explain one way to increase the frequency. [1]

Working / Answers:
(a) ________ Hz
(b) ________________________
(c) ________________________

14. [4 marks]
A 12 V battery supplies a current of 3.0 A to a circuit for 10 minutes.
(a) Calculate the total charge transferred. [2]
(b) Calculate the electrical energy supplied. [2]

Working:
(a) ___________________________________________________________
(b) ___________________________________________________________
Answers: (a) ________ C (b) ________ J

15. [5 marks]
A step-down transformer supplies a 24 V, 5.0 A lamp from a 240 V mains. Assume ideal.
(a) Calculate the secondary power. [2]
(b) Calculate the primary current. [2]
(c) State one reason why the actual primary current would be higher. [1]

Working:
(a) ___________________________________________________________
(b) ___________________________________________________________
(c) ___________________________________________________________
Answers: (a) ________ W (b) ________ A (c) ________________________

Section C: Conceptual and Applied Questions (20 marks)

16. [3 marks]
A student says: “If I double the number of turns on the secondary coil of an ideal transformer, the secondary current will double.” Explain whether this is correct, using transformer equations.

17. [3 marks]
Describe an experiment to demonstrate electromagnetic induction using a magnet, a coil, and a galvanometer. Include the observation.

18. [4 marks]
The diagram shows a DC motor.

Image pending generation: diagram for 18.

(a) State the energy conversion in the motor. [1]
(b) Explain the role of the commutator. [2]
(c) State how to reverse the direction of rotation. [1]

Answers:
(a) ________________________
(b) ________________________
(c) ________________________

19. [4 marks]
Household electrical appliances are connected in parallel, not in series.
(a) State one reason for this arrangement. [2]
(b) Explain what happens to the other appliances if one appliance in parallel fails (open circuit). [2]

Answers:
(a) ________________________
(b) ________________________

20. [6 marks]
A power transmission line uses a step-up transformer at the generating station and a step-down transformer at the consumer end.
(a) Explain why the voltage is stepped up for transmission. [3]
(b) Calculate the transmission current if 100 kW is sent at 20 kV. [2]
(c) State one environmental benefit of reducing current in the wires. [1]

Working / Answers:
(a) ___________________________________________________________
(b) ________ A
(c) ___________________________________________________________

End of Paper

Answers

TuitionGoWhere Exam Practice (AI) - Pure Physics Secondary 4 PRELIM (Version 5) Answer Key

Total Marks: 60

Section A: Structured Questions

1. [2 marks]
Expected: The neutral wire provides the return path for current to the supply and is maintained at approximately zero potential.
Marking: 1 mark for “return path / completes circuit”, 1 mark for “zero potential / reference”.

2. [1 mark]
Expected: A circuit breaker can be reset and reused; no need for replacement (or faster response).
Marking: 1 mark for any valid advantage.

3. [2 marks]
Expected: The galvanometer needle deflects momentarily in the opposite direction (to the left).
Marking: 1 mark “momentarily / briefly”, 1 mark “opposite direction / left”.
Teaching: Removing the charged rod reduces flux; Lenz’s law gives opposite induced current.

4. [2 marks]
Expected: For ideal transformer, $\frac{N_p}{N_s} = \frac{V_p}{V_s}$ .
Marking: 2 marks for correct ratio equation.

5. [2 marks]
Expected: Energy is lost as heat in the coils (resistance) and as eddy currents in the core; some flux leakage.
Marking: 1 mark for coil heating, 1 mark for core/eddy loss.

6. [2 marks]
Expected: Force is upward (away from the magnet, perpendicular to field and current).
Using Fleming’s left-hand: Field N→S (left to right), current into page, force up.
Marking: 2 marks for correct direction with rule stated or implied.

7. [2 marks]
Expected: Increase rate of change of magnetic flux (faster movement / stronger magnet); increase number of turns.
Marking: 1 mark each.

8. [3 marks]
Expected: Earth wire is safety path; normally no current. During fault (live touches casing), current flows to earth, causing breaker/fuse to cut off.
Marking: 1 mark purpose, 1 mark no current normally, 1 mark fault action.

Section B: Calculation and Data Questions

9. [2 marks]
$\frac{N_p}{N_s} = \frac{V_p}{V_s} \Rightarrow N_s = N_p \times \frac{V_s}{V_p} = 600 \times \frac{12}{240} = 30$ turns.
Answer: 30 turns.
Marking: 1 mark formula, 1 mark answer.

10. [2 marks]
$\frac{N_p}{N_s} = \frac{I_s}{I_p} \Rightarrow I_s = I_p \times \frac{N_p}{N_s} = 0.50 \times \frac{1200}{300} = 2.0$ A.
Answer: 2.0 A.
Marking: 1 mark rearrangement, 1 mark answer.

11. [3 marks]
$\eta = \frac{V_s I_s}{V_p I_p} \Rightarrow I_p = \frac{V_s I_s}{\eta V_p} = \frac{9.0 \times 2.0}{0.80 \times 230} = \frac{18}{184} = 0.098$ A.
Answer: 0.098 A (or 9.8×10⁻² A).
Marking: 1 mark efficiency eq, 1 mark substitution, 1 mark answer.

12. [3 marks]
$|\varepsilon| = N \frac{\Delta \Phi}{\Delta t} = 50 \times \frac{0.040}{0.020} = 50 \times 2 = 100$ V.
Answer: 100 V.
Marking: 1 mark Faraday eq, 1 mark sub, 1 mark answer.

13. [4 marks]
(a) $f = 1/T = 1/0.04 = 25$ Hz [2]
(b) Alternating current (AC) [1]
(c) Increase rotation speed of coil / more poles [1]
Marking: per mark as shown.

14. [4 marks]
(a) $Q = I t = 3.0 \times (10 \times 60) = 1800$ C [2]
(b) $E = V I t = 12 \times 3.0 \times 600 = 21600$ J [2]
Marking: 1 mark formula, 1 mark answer each.

15. [5 marks]
(a) $P_s = V_s I_s = 24 \times 5.0 = 120$ W [2]
(b) $P_p = P_s \Rightarrow I_p = P_p / V_p = 120 / 240 = 0.50$ A [2]
(c) Real losses (heat) mean more primary current needed [1]
Marking: as shown.

Section C: Conceptual and Applied Questions

16. [3 marks]
Incorrect. For ideal: $V_s / V_p = N_s / N_p$ and $I_s / I_p = N_p / N_s$ . Doubling $N_s$ doubles $V_s$ but halves $I_s$ (if primary fixed). So secondary current decreases, not doubles.
Marking: 1 mark correct claim, 2 marks explanation with equations.

17. [3 marks]
Connect coil to galvanometer. Move magnet in/out of coil. Observe needle deflects one way then opposite. Faster motion → larger deflection.
Marking: 1 mark setup, 1 mark action, 1 mark observation.

18. [4 marks]
(a) Electrical → kinetic (rotational) energy [1]
(b) Reverses current direction every half-turn to keep torque same direction [2]
(c) Reverse DC supply polarity or swap magnet poles [1]

19. [4 marks]
(a) Each appliance gets full mains voltage independent of others [2]
(b) Others keep working because parallel branches have separate paths [2]

20. [6 marks]
(a) Higher voltage → lower current for same power; lowers $I^2R$ heat loss in wires [3]
(b) $I = P/V = 100000 / 20000 = 5.0$ A [2]
(c) Less energy wasted → lower fuel use / emissions [1]

End of Answer Key

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