AQA GCSE Physics · 4.7

Magnetism and electromagnetism

Exam-style questions with answers for 4.7 Magnetism and electromagnetism in AQA GCSE Physics (spec 8463). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below.

All questions and answers

Question 1 · Spec 4.7.1.1 · Magnets
What happens when two like poles are brought together? [1 mark]
Answer:
They repel.
Question 2 · Spec 4.7.1.1 · Magnets
What is the difference between a permanent and an induced magnet? [2 marks]
Answer:
A permanent magnet produces its own magnetic field (1); an induced magnet becomes a magnet only when placed in a magnetic field, and loses it when removed (1).
Question 3 · Spec 4.7.1.1 · Magnets
Why does induced magnetism always cause attraction? [1 mark]
Answer:
The induced pole nearest the magnet is always the opposite pole.
Question 4 · Spec 4.7.1.2 · Magnetic fields
What is a magnetic field? [1 mark]
Answer:
The region around a magnet where a force acts on another magnet or on a magnetic material.
Question 5 · Spec 4.7.1.2 · Magnetic fields
Name four magnetic materials. [2 marks]
Answer:
Iron and steel (1); cobalt and nickel (1).
Question 6 · Spec 4.7.1.2 · Magnetic fields
How does the strength of a magnetic field change with distance? [1 mark]
Answer:
It decreases with distance from the magnet.
Question 7 · Spec 4.7.1.2 · Field lines
In which direction do magnetic field lines point? [1 mark]
Answer:
From the north (seeking) pole to the south (seeking) pole of the magnet.
Question 8 · Spec 4.7.1.2 · Plotting fields
Describe how to plot a magnetic field using a compass. [2 marks]
Answer:
Place a compass near the magnet and mark the direction of the needle (1); move the compass along and repeat, joining the marks to form a field line (1).
Question 9 · Spec 4.7.1.2 · Earth's field
What evidence shows the Earth has a magnetic core? [1 mark]
Answer:
A compass needle points north when it is away from any magnet.
Question 10 · Spec 4.7.2.1 · Electromagnetism
Describe the magnetic field around a straight current-carrying wire. [2 marks]
Answer:
Concentric circles around the wire (1); stronger closer to the wire and with a greater current (1).
Question 11 · Spec 4.7.2.1 · Solenoids
How can the magnetic field of a solenoid be made stronger? [2 marks]
Answer:
Any two from: add an iron core (1); increase the current (1); add more turns of wire (1).
Question 12 · Spec 4.7.2.1 · Electromagnets
What is an electromagnet? [1 mark]
Answer:
A solenoid with an iron core, whose magnetism can be switched on and off.
Question 13 · Spec 4.7.2.1 · Electromagnets
Give two uses of electromagnets. [2 marks]
Answer:
Any two from: scrapyard cranes (1); electric bells (1); relays (1); door locks (1).
Question 14 · Spec 4.7.2.2 · Motor effect · Higher only
What is the motor effect? [1 mark]
Answer:
A wire carrying a current in a magnetic field experiences a force.
Question 15 · Spec 4.7.2.2 · Fleming's left-hand rule · Higher only
What does each finger represent in Fleming's left-hand rule? [3 marks]
Answer:
First finger: magnetic field (1); second finger: current (1); thumb: motion (force) (1).
Question 16 · Spec 4.7.2.2 · Force on a conductor · Higher only
State the equation for the force on a conductor in a magnetic field. [1 mark]
Answer:
Force = magnetic flux density × current × length (F = BIl).
Question 17 · Spec 4.7.2.2 · Force on a conductor · Higher only
Calculate the force on a 0.2 m wire carrying 3 A in a 0.5 T field. [2 marks]
Answer:
F = BIl = 0.5 × 3 × 0.2 (1); = 0.3 N (1).
Question 18 · Spec 4.7.2.2 · Force on a conductor · Higher only
When is there no force on a current-carrying wire in a magnetic field? [1 mark]
Answer:
When the wire is parallel to the magnetic field.
Question 19 · Spec 4.7.2.3 · Electric motors · Higher only
Explain why a coil of wire rotates in a motor. [2 marks]
Answer:
Current flows in opposite directions on each side of the coil (1); so the forces on each side act in opposite directions, causing rotation (1).
Question 20 · Spec 4.7.2.3 · Electric motors · Higher only
State two ways to make a motor spin faster. [2 marks]
Answer:
Any two from: increase the current (1); use a stronger magnet (1); add more turns to the coil (1).
Question 21 · Spec 4.7.2.4 · Loudspeakers · Higher only
Explain how a loudspeaker produces sound. [3 marks]
Answer:
An alternating current flows through a coil in a magnetic field (1); the motor effect makes the coil and cone move back and forth (1); the cone vibrates the air, producing pressure variations (sound) (1).
Question 22 · Spec 4.7.3.1 · Induced potential · Higher only
What is the generator effect? [2 marks]
Answer:
When a conductor moves relative to a magnetic field, or the field around it changes (1); a potential difference is induced across its ends (1).
Question 23 · Spec 4.7.3.1 · Induced potential · Higher only
State two ways to increase the induced potential difference. [2 marks]
Answer:
Any two from: move the magnet faster (1); use a stronger magnet (1); use more turns on the coil (1).
Question 24 · Spec 4.7.3.1 · Induced potential · Higher only
Why does an induced current oppose the change that caused it? [1 mark]
Answer:
The induced current produces its own magnetic field that opposes the original change.
Question 25 · Spec 4.7.3.2 · Generators · Higher only
What is the difference between an alternator and a dynamo? [2 marks]
Answer:
An alternator uses slip rings to produce alternating current (1); a dynamo uses a split-ring commutator to produce direct current (1).
Question 26 · Spec 4.7.3.3 · Microphones · Higher only
Explain how a microphone works. [3 marks]
Answer:
Sound waves make the diaphragm vibrate (1); this moves a coil in a magnetic field (1); inducing an alternating p.d. that matches the sound wave (1).
Question 27 · Spec 4.7.3.4 · Transformers · Higher only
Describe the structure of a transformer. [2 marks]
Answer:
Two coils of wire (primary and secondary) (1); wound on an iron core (1).
Question 28 · Spec 4.7.3.4 · Transformers · Higher only
Explain how a transformer works. [3 marks]
Answer:
An alternating current in the primary coil produces a changing magnetic field in the iron core (1); this changing field passes through the secondary coil (1); inducing an alternating p.d. across it (1).
Question 29 · Spec 4.7.3.4 · Transformers · Higher only
Why must transformers use alternating current? [1 mark]
Answer:
A changing magnetic field is needed to induce a p.d., and only an alternating current produces one.
Question 30 · Spec 4.7.3.4 · Transformers · Higher only
A transformer has 200 turns on the primary and 50 on the secondary. The primary p.d. is 240 V. Calculate the secondary p.d. [2 marks]
Answer:
Vₛ = Vₚ × nₛ ÷ nₚ = 240 × 50 ÷ 200 (1); = 60 V (1).
Question 31 · Spec 4.7.3.4 · Transformers · Higher only
Is the transformer with 200 primary turns and 50 secondary turns step-up or step-down? [1 mark]
Answer:
Step-down, because the secondary has fewer turns.
Question 32 · Spec 4.7.3.4 · Transformers · Higher only
State the power equation for a 100% efficient transformer. [1 mark]
Answer:
Vₚ × Iₚ = Vₛ × Iₛ.
Question 33 · Spec 4.7.3.4 · Transformers · Higher only
A 100% efficient transformer has Vₚ = 230 V, Iₚ = 2 A and Vₛ = 46 V. Calculate Iₛ. [2 marks]
Answer:
230 × 2 = 46 × Iₛ (1); Iₛ = 10 A (1).
Question 34 · Spec 4.7.3.4 · National Grid · Higher only
Explain why step-up transformers improve the efficiency of the National Grid. [2 marks]
Answer:
They increase the p.d. and so reduce the current for the same power (1); less energy is lost as heat in the cables (1).
Question 35 · Spec 4.7.1.2 · Magnetic fields
Where is the magnetic field of a bar magnet strongest? [1 mark]
Answer:
At the poles.
Question 36 · Spec 4.7.2.1 · Solenoids
Describe the magnetic field inside a solenoid. [1 mark]
Answer:
Strong and uniform, with parallel field lines.
Question 37 · Spec 4.7.2.1 · Electromagnetism
How can you reverse the direction of the magnetic field around a wire? [1 mark]
Answer:
Reverse the direction of the current.
Question 38 · Spec 4.7.1.1 · Magnets
How can you tell if a metal bar is a permanent magnet or a magnetic material? [1 mark]
Answer:
Only a permanent magnet can repel another magnet.
Question 39 · Spec 4.7.2.2 · Motor effect · Higher only
What happens to the force on a wire if both the current and field direction are reversed? [1 mark]
Answer:
The force stays in the same direction.
Question 40 · Spec 4.7.2.3 · Electric motors · Higher only
What is the function of the split-ring commutator in a motor? [1 mark]
Answer:
It reverses the current in the coil every half turn so it keeps rotating in the same direction.
Question 41 · Spec 4.7.3.1 · Induced potential · Higher only
What happens when a magnet is held still inside a coil? [1 mark]
Answer:
No p.d. is induced, because the magnetic field is not changing.
Question 42 · Spec 4.7.3.2 · Generators · Higher only
What happens to the output of a generator if it rotates faster? [2 marks]
Answer:
The peak p.d. increases (1); and the frequency of the a.c. increases (1).
Question 43 · Spec 4.7.1.2 · Field lines
What do closely spaced field lines show? [1 mark]
Answer:
A stronger magnetic field.
Question 44 · Spec 4.7.2.2 · Force on a conductor · Higher only
What is the unit of magnetic flux density? [1 mark]
Answer:
The tesla (T).
Question 45 · Spec 4.7.2.1 · Electromagnets
Why is iron used for the core of an electromagnet? [1 mark]
Answer:
It is magnetically soft: it magnetises strongly but loses its magnetism when the current is switched off.
Question 46 · Spec 4.7.3.3 · Microphones · Higher only
How is a microphone similar to and different from a loudspeaker? [2 marks]
Answer:
Both have a coil in a magnetic field attached to a diaphragm or cone (1); a microphone uses the generator effect to turn sound into a.c., while a loudspeaker uses the motor effect to turn a.c. into sound (1).
Question 47 · Spec 4.7.3.4 · Transformers · Higher only
State the transformer turns equation. [1 mark]
Answer:
Vₚ ÷ Vₛ = nₚ ÷ nₛ.
Question 48 · Spec 4.7.1.1 · Magnets
Name the two poles of a magnet. [1 mark]
Answer:
North (seeking) and south (seeking) poles.
Question 49 · Spec 4.7.2.1 · Electromagnetism
Who first discovered that a current produces a magnetic field? [1 mark]
Answer:
Hans Christian Ørsted (1820).
Question 50 · Spec 4.7.1.2 · Field lines
Describe the magnetic field pattern around a bar magnet. [2 marks]
Answer:
Field lines loop from the north pole round to the south pole (1); they are closest together at the poles, where the field is strongest (1).

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