OxfordAQA International GCSE Physics: Electromagnetic induction, generators and the motor effect (9203) – Practice Questions

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 – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions are aligned to the OxfordAQA International GCSE Physics (9203) specification, version 5.2, for exams May/June 2018 onwards. They cover sections 3.6.1 (Generating electricity) and 3.6.4 (The motor effect). The qualification is untiered. Read the study guide first if the ideas are new, and use the revision notes to check your recall. The course hub is at OxfordAQA International GCSE Physics and the checklist tracks your progress. The free diagnostics show which topics to practise first.

Questions

1. (a) Give the two situations in which a conductor develops a potential difference between its ends. [2] (b) Name this effect. [1]

2. A coil is connected to a sensitive centre-zero meter. A student pushes a bar magnet into the coil, holds it still inside, then pulls it out. (a) Describe what the meter shows at each stage. [3] (b) State two changes that would increase the reading when the magnet is pushed in. [2]

3. The north pole of a bar magnet is lowered towards the top end of a vertical closed coil. (a) State the pole that forms at the top end of the coil. [1] (b) Explain why the student has to do work to push the magnet in. [2] (c) The magnet is now lifted away. State the pole at the top end of the coil. [1]

4. A student drops the same magnet from the same height through four coils of the same area. A data logger records the peak pd.

Number of turns	50	100	150	200
Peak pd (mV)	1.2	2.4	3.6	4.8

(a) Describe how the peak pd changes with the number of turns. [2] (b) Predict the peak pd for a coil of 250 turns. [1] (c) State two variables that were controlled. [2] (d) State one other change that would increase the peak pd. [1]

5. The pd generated by a simple alternator is recorded. The coil makes one rotation for each cycle of the output.

Time (ms)	0	10	20	30	40	50	60
pd (V)	0	4.0	0	-4.0	0	4.0	0

(a) State the peak pd. [1] (b) Calculate the frequency of the output. [3] (c) Calculate the number of rotations the coil makes in one minute. [2] (d) The coil is turned twice as fast. State the new frequency and what happens to the peak pd. [2]

6. (a) Describe how the pd-time graph from a dynamo differs from the graph from an alternator. [2] (b) Explain why the output of an alternator is alternating current. [2]

7. Describe how a fuel-burning power station uses a turbine to generate electricity. [4]

8. (a) State the condition under which a current-carrying wire in a magnetic field experiences no force. [1] (b) State three ways of increasing the force on the wire. [3]

9. (a) Use Fleming’s left-hand rule to give the direction of the force on a straight wire in each case. (i) Field points up the page, current points out of the page. [1] (ii) Field points from left to right, current points up the page. [1] (iii) Field points out of the page, current points from left to right. [1] (b) In case (a)(i) the current and the field are both reversed. Explain what happens to the force. [2]

10. A rectangular coil carries a current in a magnetic field and is free to turn. (a) Explain why the coil turns. [3] A straight wire of fixed length in a field is carrying different currents. The force on it is measured.

Current (A)	1.5	3.0	4.5	6.0
Force (N)	0.054	0.108	0.162	0.216

(b) Describe the relationship between the force and the current. [2] (c) Predict the force when the current is 7.5 A. [1] (d) State two other changes that would increase the force. [2]

11. A hand-cranked generator lights a small lamp. (a) Suggest four changes to the generator that would increase the pd it produces. [4] (b) The student notices the handle is harder to turn when the lamp is connected than when it is disconnected. Explain why. [3]

Answers

1. (a) The conductor moves relative to a magnetic field, so it cuts the field lines [1]. The magnetic field around the conductor is changing [1]. (b) The generator effect [1]. [3] Examiner insight: Say that the conductor is moving across the field, not just “in a field”. A stationary conductor in a steady field gains nothing.

2. (a) Pushed in: the meter deflects one way [1]. Held still: zero reading [1]. Pulled out: the meter deflects the opposite way [1]. (b) Push the magnet in faster [1]. Use a coil with more turns, or a stronger magnet [1]. [5] Examiner insight: Give a separate statement for each of the three stages, including the direction of the deflection. A reading of zero when the magnet is still is worth stating clearly.

3. (a) North [1]. (b) The induced current has a magnetic field that opposes the field of the magnet, so the coil repels the approaching north pole [1]. Work done against this repulsion is the energy transferred to the circuit [1]. (c) South [1]. [4] Examiner insight: Use the word opposes, and link the repulsion to the movement. Answers that only name the pole for the approach do not usually explain the extra effort.

4. (a) A coil with more turns gives a larger peak pd [1]. It is directly proportional: 1.2 mV for every 50 turns, so doubling the turns doubles the pd [1]. (b) 5 × 1.2 = 6.0 mV [1]. (c) Any two from: the same magnet, the same drop height (same speed), the same coil area [2]. (d) A stronger magnet, a larger coil area, or a faster drop (any one) [1]. [6] Examiner insight: Quote values to show the proportion, such as 1.2 mV per 50 turns. Saying “it goes up” alone describes less than the table shows.

5. (a) 4.0 V [1]. (b) The peaks are at 10 ms and 50 ms, so the period is 40 ms = 0.040 s [1]. Frequency = 1 ÷ period = 1 ÷ 0.040 [1]. Frequency = 25 Hz [1]. (c) 25 rotations per second [1]. 25 × 60 = 1500 rotations per minute [1]. (d) The frequency doubles to 50 Hz [1]. The peak pd increases [1]. [8] Examiner insight: Convert milliseconds to seconds before using the frequency relationship and show the unit. Choosing 20 ms (a half cycle) as the period is the usual slip.

6. (a) The dynamo graph stays on one side of the axis (the same direction) [1]. It is a series of humps that fall to zero, while the alternator graph goes above and below the axis [1]. (b) Each side of the coil moves upwards through the field and then downwards [1]. The polarity of the induced pd therefore flips twice per rotation [1]. [4] Examiner insight: Mention the reversal of direction, not just that the output changes size. Both outputs vary in size, so size alone does not separate ac from dc.

7. The fuel is burned to heat water [1]. The water turns to steam, which pushes the blades of the turbine [1]. The turbine turns a coil between magnets [1]. The coil cuts the magnetic field lines, so a pd is induced across it [1]. [4] Examiner insight: Give the steps in order, ending with the induced pd. Saying “the turbine makes the electricity” skips the physics that earns credit.

8. (a) The wire is parallel to the magnetic field [1]. (b) Increase the strength of the magnetic field [1]. Increase the current [1]. Increase the length of wire in the field [1]. [4] Examiner insight: Say that the field is stronger, not that the magnet is bigger. More turns is a generator factor and does not belong in this list.

9. (a)(i) The first finger points up the page and the second finger points out of the page. The thumb points to the left [1]. (ii) The first finger points right, the second finger points up the page, and the thumb points into the page [1]. (iii) The first finger points out of the page, the second finger points right, and the thumb points down the page [1]. (b) Reversing the current alone reverses the force [1]. Reversing the field as well reverses it again, so the force is back in the original direction [1]. [5] Examiner insight: Draw the three directions at right angles to check them. Using the right hand gives the opposite direction every time.

10. (a) The two long sides of the coil carry current in opposite directions [1]. Fleming’s rule then gives opposite forces on those sides [1]. Together they give a turning effect [1]. (b) The force increases as the current increases [1]. It is directly proportional, 0.036 N for every 1.0 A [1]. (c) 7.5 × 0.036 = 0.270 N [1]. (d) A stronger magnetic field [1]. A longer length of wire in the field [1]. [8] Examiner insight: Opposite forces on opposite sides is the key idea for part (a). Give both the pattern and a figure from the table when you describe a relationship.

11. (a) Turn the handle faster [1]. Use a stronger magnet [1]. Use more turns on the coil [1]. Use a larger coil [1]. (b) With the lamp connected the circuit is complete, so an induced current flows [1]. The current has a magnetic field that opposes the movement of the coil [1]. More work has to be done against this opposition, and that work is the energy transferred to the lamp [1]. [7] Examiner insight: Part (b) needs a complete circuit mentioned first. Without a current there is no opposing field, so the handle is easier to turn.

Where marks are usually lost

• Writing “the magnet makes a current” without saying the magnet or coil must be moving.
• Forgetting that a complete circuit is needed for an induced current, while the pd can exist without one.
• Describing the induced field as stopping the motion, rather than opposing it.
• Using the period as half a cycle when reading a graph, so the frequency is double the true value.
• Giving a dynamo graph that crosses the axis.
• Mixing up the first and second fingers in Fleming’s rule, or using the right hand.
• Treating reversal of one factor and reversal of both as the same.
• Listing more turns or a larger coil as ways to increase the force on a straight wire.

Next steps

• Review the revision notes for the condensed facts.
• Re-read the study guide for the worked examples.
• Return to the course hub and tick off your checklist.
• Take one of the free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

OxfordAQA International GCSE Physics (9203), version 5.2, for exams May/June 2018 onwards, published by OxfordAQA, sections 3.6.1 and 3.6.4.