Pearson Edexcel GCSE Combined Science · P12

Magnetism and the motor effect

50 revision questions with answers for P12 Magnetism and the motor effect in Pearson Edexcel GCSE Combined Science (spec 1SC0). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below.

All 50 questions and answers

Question 1 · Spec P12.1
What happens when unlike magnetic poles approach?
Answer:
They attract.
Question 2 · Spec P12.1
What happens when like magnetic poles approach?
Answer:
They repel.
Question 3 · Spec P12.4
Where is a bar magnet's field strongest?
Answer:
Near its poles, where field lines are most concentrated.
Question 4 · Spec P12.3
What is a permanent magnet?
Answer:
A material that retains its magnetism and produces its own magnetic field.
Question 5 · Spec P12.3
What is an induced magnet?
Answer:
A material that becomes magnetised in an external magnetic field.
Question 6 · Spec P12.2
Name four magnetic materials.
Answer:
Iron, steel, cobalt and nickel.
Question 7 · Spec P12.2
Why is iron useful for temporary magnets while steel can suit permanent magnets?
Answer:
Iron is magnetised and demagnetised readily; steel retains magnetism more strongly.
Question 8 · Spec P12.3
How can an initially unmagnetised iron object be attracted to a magnet?
Answer:
The external field induces magnetism in the iron.
Question 9 · Spec P12.3
Why is either pole able to attract unmagnetised iron?
Answer:
An opposite pole is induced at the nearer end, producing attraction.
Question 10 · Spec P12.3
What usually happens to temporary induced magnetism when the external field is removed?
Answer:
Most or all of it is lost quickly.
Question 11 · Spec P12.4
What is a magnetic field?
Answer:
The region where magnetic interactions exert forces.
Question 12 · Spec P12.4
Which direction do field lines run outside a bar magnet?
Answer:
From north to south.
Question 13 · Spec P12.4
How is magnetic field direction defined using a compass?
Answer:
The north-seeking needle end points in the local field direction.
Question 14 · Spec P12.4
What does close field-line spacing indicate?
Answer:
A stronger field.
Question 15 · Spec P12.4
How is a uniform field represented?
Answer:
Straight parallel field lines with equal spacing.
Question 16 · Spec P12.5
How can a plotting compass map a field?
Answer:
Mark successive needle directions, join the marks into curves and add direction arrows.
Question 17 · Spec P12.5
Why can iron filings show shape but not field direction?
Answer:
Their alignment reveals the pattern, but no north-to-south arrow convention is visible.
Question 18 · Spec P12.6
What does a compass's alignment provide evidence for?
Answer:
The Earth has a magnetic field associated with magnetic behaviour in its core.
Question 19 · Spec P12.5
Why may a compass turn differently near a bar magnet?
Answer:
It responds to the combined local field, which may differ from Earth's field alone.
Question 20 · Spec P12.4
What is the force direction on a test north pole?
Answer:
Along the magnetic field direction at that point.
Question 21 · Spec P12.7
What is produced around a current-carrying wire?
Answer:
A magnetic field.
Question 22 · Spec P12.7
How can current's magnetic effect be demonstrated?
Answer:
A nearby compass deflects when current is switched on; reversing current reverses the deflection.
Question 23 · Spec P12.7
What is the field shape around a long straight wire?
Answer:
Concentric circles centred on the wire.
Question 24 · Spec P12.7
How does the right-hand grip rule show field direction?
Answer:
Thumb follows conventional current; curled fingers show the field direction.
Question 25 · Spec P12.7
What happens if current through the wire is reversed?
Answer:
The magnetic field direction reverses.
Question 26 · Spec P12.8
How does increasing current affect field strength at fixed distance?
Answer:
It increases the strength.
Question 27 · Spec P12.8
How does increasing distance from the wire affect field strength?
Answer:
It decreases the strength.
Question 28 · Spec P12.9
What is a solenoid?
Answer:
A coil of wire that produces a magnetic field when current flows.
Question 29 · Spec P12.9
Describe the field inside a solenoid.
Answer:
Strong and nearly uniform along its centre.
Question 30 · Spec P12.9
Why is the solenoid's central field stronger than that of a single turn?
Answer:
Fields from individual turns add together.
Question 31 · Spec P12.9
Why is the field weaker outside a solenoid?
Answer:
Fields from different turns partially oppose and cancel outside the central region.
Question 32 · Spec P12.9
How does adding an iron core affect a solenoid?
Answer:
The core becomes magnetised and increases the field strength.
Question 33 · Spec P12.9
Why can an electromagnet be switched off?
Answer:
Its current-produced field disappears when current stops, and a suitable temporary core loses most magnetism.
Question 34 · Spec P12.9
How can a solenoid's poles be reversed?
Answer:
Reverse the current through the coil.
Question 35 · Spec P12.10 · Higher only
What is the motor effect?
Answer:
A current-carrying conductor in a magnetic field experiences a force.
Question 36 · Spec P12.10 · Higher only
What force acts on the magnet when it pushes the conductor?
Answer:
An equal and opposite force, as part of the interaction.
Question 37 · Spec P12.11 · Higher only
Why does the conductor experience magnetic force?
Answer:
Its current-produced field interacts with the external magnetic field.
Question 38 · Spec P12.12 · Higher only
State Fleming's left-hand rule finger meanings.
Answer:
First finger: field; second finger: conventional current; thumb: force, all mutually perpendicular.
Question 39 · Spec P12.12 · Higher only
What happens to force if only current reverses?
Answer:
Force direction reverses.
Question 40 · Spec P12.12 · Higher only
What happens to force if only the magnetic field reverses?
Answer:
Force direction reverses.
Question 41 · Spec P12.12 · Higher only
What happens to force direction if both current and field reverse?
Answer:
It stays the same.
Question 42 · Spec P12.13 · Higher only
What orientation gives zero motor-effect force on a straight wire?
Answer:
Current parallel to the magnetic field.
Question 43 · Spec P12.13 · Higher only
State the force equation for a perpendicular current-carrying conductor.
Answer:
F = BIl.
Question 44 · Spec P12.13 · Higher only
Give units for B, I and l.
Answer:
Tesla, amperes and metres respectively; force is in newtons.
Question 45 · Spec P12.13 · Higher only
Find force for B = 0.5 T, I = 4 A and l = 0.20 m.
Answer:
F = 0.5 × 4 × 0.20 = 0.40 N.
Question 46 · Spec P12.13 · Higher only
Find current for F = 0.60 N, B = 0.30 T and l = 0.50 m.
Answer:
I = F/(Bl) = 0.60/(0.30 × 0.50) = 4.0 A.
Question 47 · Spec P12.13 · Higher only
Find B for F = 0.12 N, I = 2 A and l = 0.30 m.
Answer:
B = F/(Il) = 0.12/(2 × 0.30) = 0.20 T.
Question 48 · Spec P12.13 · Higher only
Find active length for F = 0.08 N, B = 0.4 T and I = 2 A.
Answer:
l = F/(BI) = 0.08/(0.4 × 2) = 0.10 m.
Question 49 · Spec P12.13 · Higher only
What if both current and active length double at fixed perpendicular field?
Answer:
The force becomes four times larger.
Question 50 · Spec P12.13 · Higher only
Why use only the wire length inside the magnetic field in F = BIl?
Answer:
Only that length experiences the specified field and contributes that force.

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