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4.4.2Electricity and Magnetism

Demonstrating Induction — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions

5 min read 9 parts Lesson 47 of 65 1 quiz

📚 Cambridge IGCSE Physics 0625 Hub / Topical Revision
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Lesson summary

4.4.2 Demonstrating Induction — IGCSE PHYSICS notes: Describe simple experiments that show electromagnetic induction and predict the meter readings.Equipment — a coil of insulated wire, a sensitive centre-zero voltmeter or galvanometer, connecting wires and a bar magnet.Centre-ze…

  • Centre-zero meter
  • No battery
  • Uses of induction
  • Relative motion
  • Increasing the e.m.f
  • Along the field

Part 1 of 4Apparatus

Equipment
  • Equipment a coil of insulated wire, a sensitive centre-zero voltmeter or galvanometer, connecting wires and a bar magnet.
Centre-zero meter
  • Centre-zero meter it shows the sign of the e.m.f., which reverses when the motion reverses.
No battery
  • No battery any reading comes only from induction.
Uses of induction
  • Uses of induction electrical generators convert mechanical energy to electrical energy, and transformers are used in power transmission.

Part 2 of 4Making the effect easier to see

Coil
  • Coil add more turns.
Magnet
  • Magnet use a stronger magnet.
Speed
  • Speed move the magnet faster.
Core
  • Core add a soft-iron core in two-coil experiments.
Meter
  • Meter use a more sensitive meter or an oscilloscope.
  • A magnet swinging in and out of a coil gives a roughly sinusoidal trace.

Part 3 of 4Explaining the observations

Chain of reasoning
  • Chain of reasoning state what is changing, what that does to the field linking the coil and what the meter shows.
Faster magnet
  • Faster magnet it cuts field lines at a greater rate, so a larger e.m.f. is induced.
Switch left closed
  • Switch left closed the current is steady, so the field linking the second coil is steady and no e.m.f. is induced.
Safety
  • Safety connect the cell only briefly, because the low-resistance coil can heat up, and keep magnets away from the meter.

Part 4 of 4More from the specification

1
Electromagnetic induction and electric motor action
  • Electromagnetic induction and electric motor action moving conductors cut magnetic lines of force, driving induced currents that power electric motor armatures.
2
Permanent magnet
  • Magnet whose field is always there.
3
Primary
  • Input coil.
4
Solenoid
  • Long coil of wire carrying a current
5
Conductor
  • Material that allows current to flow.
6
Brushes
  • Carbon contacts pressing on the slip rings.
7
Alternating current
  • Current that continually reverses direction.
8
Potential difference
  • Work done by a unit charge passing through a component.
9
Step-up transformer
  • Transformer with more turns on the secondary, raising the voltage.
10
Step-down transformer
  • Transformer with fewer turns on the secondary, lowering the voltage.
11
IpVp
IsVs
What the symbols mean: V = voltage (V) · N = number of turns · I = current (A) · p = primary coil · s = secondary coil
12
Stationary magnet
  • Stationary magnet when the magnet is held still, the voltmeter reads zero because no field lines are being cut.

Key terms

TermMeaning
InductionProduction of an e.m.f. by a changing magnetic field.
Centre-zero meterMeter with zero in the middle of the scale so it shows direction.
Relative motionMovement of the conductor and field with respect to each other.
Field lines cutField lines crossed by a conductor, producing an e.m.f.
Iron coreSoft iron that concentrates the field between coils.

Avoid these mistakes

1
Using a meter with zero at the end of the scale — it cannot show reversal of direction.
2
Saying current is induced while the magnet is at rest in the coil — no relative motion means no e.m.f.
3
Forgetting that closing the switch gives a brief kick, not a steady reading.
4
Describing the effect without mentioning relative motion or a changing field.

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