6 · IGCSE Physics
Electromagnetic induction
Push a bar magnet into a coil and pull it out again, then watch the voltmeter and the voltage–time graph. Change the speed, the number of turns and the magnet strength to see what controls the size and direction of the induced voltage.
- Magnet distance from coil centre
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- Magnet speed
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- Flux linkage NΦ
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- Induced voltage ε
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- Largest |ε| so far
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- Coil end facing magnet
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Model
ε = −N ΔΦ/Δt
Φ = B A (flux through one turn)
A = π × (0.0200 m)² = 1.26 ×10⁻³ m²
B is the field in the coil when the magnet is centred in it.
ε = −N ΔΦ/Δt
Φ = B A (flux through one turn)
A = π × (0.0200 m)² = 1.26 ×10⁻³ m²
B is the field in the coil when the magnet is centred in it.
Try this
- In Auto mode, read the largest |ε| at 0.5 m s⁻¹, press Reset, then repeat at 1.0 m s⁻¹. How does the peak change, and what happens to the length of each pulse?
- Keep the speed fixed and compare 100, 200 and 400 turns, then change B from 0.25 T to 0.50 T. Which quantity is the voltage proportional to in each case?
- Switch to Manual, push the magnet fully in and hold it still: the flux linkage is at its largest, yet ε is zero. Now pull it out and note which way the meter swings and which pole the coil end becomes.
Common error: saying a magnet resting inside a coil induces a voltage – a voltage is only induced while the magnetic field through the coil is changing, and it is larger for faster motion, more turns or a stronger magnet.