IGCSE Physics: Electricity and Magnetism — Practice Questions (Cambridge 0625)

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs — Cambridge International holds copyright in its own papers. Use these alongside the official past papers available free from your board.

Tier note: question 5, marked (Extended), asks how the strength of an electromagnet’s field changes, which is Supplement content of the 0625 syllabus (4.5.3 Supplement 4–5). Everything else is 0625 Core, including questions 7 and 8 on magnetism (4.1 Core).

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Questions

1. A resistor has a potential difference of 12 V across it and a current of 0.40 A in it. Calculate its resistance. [2]

2. A 4.0 Ω resistor and a 6.0 Ω resistor are connected in series to a 5.0 V battery.

(a) Calculate the combined resistance. [1]

(b) Calculate the current in the circuit. [1]

3. State two differences between the current in a series circuit and the current in a parallel circuit. [2]

4. A 2.0 kW kettle is switched on for 3.0 minutes. Calculate the energy it transfers, in joules. [2]

5. (Extended) Describe how to make a simple electromagnet stronger. Give two ways. [2]

6. State the purpose of a fuse in a plug and explain how it works. [2]

7. A student has three metal bars that look the same. One is a permanent magnet, one is unmagnetised iron and one is copper. Describe how the student can identify each bar using a bar magnet with labelled poles. [3]

8. (a) State what is meant by a magnetic field. [1] (b) Describe how a small compass is used to find the direction of the magnetic field at a point near a bar magnet. [1] (c) A scrap-yard crane uses an electromagnet with a soft-iron core. Explain why the core is made of soft iron rather than steel. [2]

Answers

1. R = V ÷ I [1] = 12 ÷ 0.40 = 30 Ω [1].

Common mistake: dividing the wrong way round (I ÷ V) or multiplying. Write V = IR first and rearrange.

2. (a) 4.0 + 6.0 = 10 Ω [1]. (b) I = V ÷ R = 5.0 ÷ 10 = 0.50 A [1].

Common mistake: using the resistance of only one resistor. In series, the resistances add.

3. In a series circuit the current is the same at every point [1]; in a parallel circuit the current from the source divides between the branches, so the current from the source is larger than the current in each branch [1] (Extended: the branch currents add up to the total).

4. E = Pt = 2000 W × 180 s [1] = 360 000 J (3.6 × 10⁵ J) [1].

5. (Extended) Any two of: more turns on the coil [1]; a larger current [1]; a soft-iron core in the coil [1]. Maximum 2 marks.

6. A fuse protects the wiring (and the appliance) from too large a current, which could cause overheating or fire [1]. If the current is larger than the fuse rating, the fuse wire heats up and melts, breaking the circuit [1].

7. Bring one pole of the bar magnet up to each end of each bar in turn. The bar that is repelled by one end is the permanent magnet (only a magnet can repel another magnet) [1]. The bar that is attracted at both ends by either pole, but never repelled, is the iron: magnetism is induced in it [1]. The bar that is neither attracted nor repelled is the copper, which is non-magnetic [1].

Common mistake: using attraction to identify the magnet. The iron bar is attracted too, so only repulsion proves a bar is a magnet.

8. (a) A region in which a magnetic pole experiences a force [1]. (b) Place the compass at the point: the field direction is the direction in which the compass needle’s north pole points [1]. (c) Soft iron is magnetised easily but loses its magnetism when the current is switched off, so the crane can drop the scrap [1]. Steel would stay magnetised (it forms a permanent magnet), so the scrap would not be released [1].

Common mistake: saying soft iron is used because it is “a stronger magnet”. The reason is that it is a temporary magnet.

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Where marks are usually lost

• Forgetting to convert minutes to seconds or kW to W in E = Pt.
• Saying current is “used up” around a series circuit.
• Saying a fuse protects the person rather than the wiring.