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Magnetism and induction

Describe magnetic fields, electromagnets, motor effects and electromagnetic induction at IGCSE level.

12 free questions · Notes · Worked solutions

Practise this topic

What you will practise

  • Describe magnetic field patterns and pole interactions.
  • Explain how current creates a magnetic field.
  • Describe factors affecting an electromagnet.
  • Explain electromagnetic induction and ways to increase induced voltage.

Revision notes

Magnets and fields

Like poles repel and unlike poles attract. Magnetic field lines point from north to south outside a magnet; closer lines indicate a stronger field. A compass aligns with the local field.

Current and electromagnets

A current-carrying wire produces a magnetic field. A solenoid's field resembles a bar magnet; adding an iron core, increasing current or increasing coil turns strengthens an electromagnet.

Motor effect

A current-carrying conductor in a magnetic field can experience a force. Reversing the current or magnetic field reverses the force direction. A coil can rotate when forces act on opposite sides.

Induction

An emf is induced when magnetic flux through a conductor or coil changes. Faster relative motion, a stronger magnetic field or more turns increases induced emf. The induced effect opposes the change causing it.

A worked example

A coil is moved into a magnetic field and produces an induced voltage of 0.4 V. Describe two changes that would increase the induced voltage, and state what happens if the coil is held still in the field.

  1. Move the coil faster so magnetic flux changes more rapidly.
  2. Use a stronger magnetic field or increase the number of coil turns.
  3. When the coil is held still in a steady field, flux is not changing and no emf is induced.

Faster movement and a stronger field or more turns increase emf; held still gives zero induced emf.

Try it yourself

These are original practice questions, not official past-paper questions. Practice points count correct final answers; working is not automatically assessed.

Choose a question to begin.
Question 1 · Standard1 practice point

What happens when two north poles are brought close together?

Need a hint?

Like magnetic poles repel.

Worked solution
  1. Both poles are north, so they repel.
Question 2 · Standard1 practice point

What field is produced around a straight wire carrying current?

Need a hint?

Use the field pattern around a current-carrying conductor.

Worked solution
  1. The magnetic field lines form concentric circles around the wire.
Question 3 · Standard1 practice point

Which change would make a solenoid electromagnet stronger?

Need a hint?

Consider how field strength depends on current and coil turns.

Worked solution
  1. More turns produce a stronger combined magnetic field.
Question 4 · Standard1 practice point

When is an emf induced in a coil?

Need a hint?

Induction requires a change in magnetic flux linkage.

Worked solution
  1. A changing flux induces an emf.
Question 5 · Standard2 practice points

A solenoid has 200 turns. It is replaced by one with 400 turns while current and core remain the same. By what factor does the field strength increase in the simple proportional model?

Need a hint?

Compare the turn counts.

Worked solution
  1. 400/200=2.
  2. The field is twice as strong in this simplified model.
Question 6 · Stretch3 practice points

A coil has 50 turns. A magnet is moved through it once and an induced voltage is detected. If the same motion is repeated in half the time, by what factor does the average induced voltage change, assuming the same flux change?

Need a hint?

Induced emf depends on rate of flux change.

Worked solution
  1. The same flux change occurs in half the time.
  2. Rate of change doubles.
  3. Average induced voltage doubles: factor 2.
Question 7 · Standard2 practice points

A current of 3 A flows through a solenoid. The current is increased to 6 A while turns and core remain fixed. By what factor does its field strength increase in the simple proportional model?

Need a hint?

For fixed turns and core, compare the currents.

Worked solution
  1. 6/3=2.
  2. The field strength doubles.
Question 8 · Standard2 practice points

A coil has 100 turns and an average induced emf of 0.2 V. If the same flux change per turn occurs in a 300-turn coil, find the induced emf in volts.

Need a hint?

Induced emf is proportional to number of turns for the same flux change.

Worked solution
  1. Turn count increases by 300/100=3.
  2. Emf=0.2×3=0.6 V.
Question 9 · Standard2 practice points

A magnet is pushed into a coil in 2 s. It is then pushed in the same way in 1 s. How does the average induced emf compare in the second movement, assuming equal flux change?

Need a hint?

Compare flux-change rate for equal changes over different times.

Worked solution
  1. The second movement takes half as long.
  2. The flux-change rate is twice as large.
  3. Average induced emf is twice as large.
Question 10 · Standard2 practice points

An induced emf is 1.5 V when a magnet moves through a coil. If it is moved three times faster with all else fixed, estimate the induced emf using direct proportionality.

Need a hint?

Multiply the emf by the speed factor.

Worked solution
  1. Emf is proportional to the rate of flux change.
  2. 1.5×3=4.5 V.
Question 11 · Standard2 practice points

A wire carrying current experiences a 2 N magnetic force. If the current is reversed with field unchanged, what is the magnitude of the force?

Need a hint?

Reversing current changes direction, not magnitude, when its size is unchanged.

Worked solution
  1. The same current magnitude flows in the reversed direction.
  2. The magnetic force magnitude remains 2 N.
Question 12 · Foundation2 practice points

A coil is stationary in a steady magnetic field for 5 s. What is the induced emf during that interval?

Need a hint?

Is the magnetic flux changing?

Worked solution
  1. The coil and field are stationary, so flux is constant.
  2. No emf is induced: 0 V.

Coverage and sources

Selected IGCSE concepts, with a mix of introductory and more demanding questions. Check your own specification. AI drafted; independent teacher review is pending. Editorial details.

Cambridge IGCSE Physics 0625 syllabus

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