Magnetic fields & induction worksheet with answers

Free printable Magnetic fields & induction worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

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1.Easy

A solenoid 40 cm long carries 1.5 A. How many turns N must it have for a flux density of 4.712 mT inside?

I = 1.5 AL = 40 cmB = 4.712 mTμ₀ = 4π × 10⁻⁷ T·m/A

N =

2.Easy

A straight wire 100 cm long carries 20 A at an angle of 30° to a uniform magnetic field of 0.12 T. Find the magnitude of the force F on the wire.

B = 0.12 TI = 20 AL = 100 cmθ = 30°

F = N

3.Medium

A coil of 250 turns, area 20 cm² and resistance 8 Ω forms a closed circuit. A uniform field perpendicular to the coil rises steadily from 0.05 T to 0.65 T in 50 ms. Find the average induced current I.

N = 250A = 20 cm²B: 0.05 T → 0.65 TΔt = 50 msR = 8 Ω

I = mA

4.Medium

A coil of 500 turns has an area of 200 cm². The coil sits in a uniform field of 0.2 T perpendicular to its plane, and the field is switched off in 250 ms. Find the average induced emf ε.

N = 500A = 200 cm²B = 0.2 TΔt = 250 ms

ε = V

5.Hard

The current in a 40 mH inductor changes steadily from 1 A to 4 A in 5 ms. Find the magnitude of the self-induced emf ε.

L = 40 mH1 A → 4 AΔt = 5 ms

ε = V

6.Hard

A short coil of 100 turns is wound tightly round the middle of a long solenoid of 2000 turns, length 30 cm and diameter 4 cm. The current in the solenoid changes at 100 A/s. Find the emf ε induced in the short coil.

N₁ = 2000N₂ = 100l = 30 cm⌀ = 4 cmdi/dt = 100 A/sμ₀ = 4π × 10⁻⁷ T·m/A

ε = mV

Answer key

1. N = 999.9
2. F = 1.2 N
3. I = 750 mA
4. ε = 8 V
5. ε = 24 V
6. ε = 105.3 mV

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