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 straight wire 25 cm long lies at 30° to a uniform magnetic field of 0.2 T. The magnetic force on it is 0.2 N. Find the current I.

B = 0.2 TF = 0.2 NL = 25 cmθ = 30°

I = A

2.Easy

A proton moves at 6 × 10⁶ m/s at an angle of 45° to a uniform magnetic field of 0.05 T. Find the magnitude of the magnetic force F on it.

|q| = 1.602 × 10⁻¹⁹ Cv = 6 × 10⁶ m/sB = 0.05 Tθ = 45°

F = fN

3.Medium

A proton moves at 2.5 × 10⁵ m/s perpendicular to a uniform magnetic field of 0.25 T. Find the radius r of its circular path.

m = 1.673 × 10⁻²⁷ kg|q| = 1.602 × 10⁻¹⁹ Cv = 2.5 × 10⁵ m/sB = 0.25 T

r = cm

4.Medium

An electron moves at 2.5 × 10⁶ m/s perpendicular to a uniform magnetic field of 10 mT. Find the radius r of its circular path.

m = 9.109 × 10⁻³¹ kg|q| = 1.602 × 10⁻¹⁹ Cv = 2.5 × 10⁶ m/sB = 10 mT

r = cm

5.Hard

The current in a 5 mH inductor changes steadily from 1 A to 0 A in 10 ms. Find the magnitude of the self-induced emf ε.

L = 5 mH1 A → 0 AΔt = 10 ms

ε = V

6.Hard

A short coil of 100 turns is wound tightly round the middle of a long solenoid of 500 turns, length 40 cm and diameter 3 cm. The current in the solenoid changes at 20 A/s. Find the emf ε induced in the short coil.

N₁ = 500N₂ = 100l = 40 cm⌀ = 3 cmdi/dt = 20 A/sμ₀ = 4π × 10⁻⁷ T·m/A

ε = mV

Answer key

1. I = 8 A
2. F = 33.98 fN
3. r = 1.044 cm
4. r = 0.1422 cm
5. ε = 0.5 V
6. ε = 2.221 mV

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