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 20 cm long lies at 90° to a uniform magnetic field of 0.08 T. The magnetic force on it is 0.16 N. Find the current I.

B = 0.08 TF = 0.16 NL = 20 cmθ = 90°

I = A

2.Easy

A straight wire 10 cm long carries 3 A at an angle of 45° to a uniform magnetic field of 0.05 T. Find the magnitude of the force F on the wire.

B = 0.05 TI = 3 AL = 10 cmθ = 45°

F = N

3.Medium

An electron moves at 2.5 × 10⁶ m/s perpendicular to a uniform magnetic field of 2 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 = 2 mT

r = cm

4.Medium

A proton moves at 4 × 10⁵ m/s perpendicular to a uniform magnetic field of 0.2 T. Find the radius r of its circular path.

m = 1.673 × 10⁻²⁷ kg|q| = 1.602 × 10⁻¹⁹ Cv = 4 × 10⁵ m/sB = 0.2 T

r = cm

5.Hard

The current in a 25 mH inductor changes steadily from 6 A to 1 A in 20 ms. Find the magnitude of the self-induced emf ε.

L = 25 mH6 A → 1 AΔt = 20 ms

ε = V

6.Hard

A short coil of 50 turns is wound tightly round the middle of a long solenoid of 1000 turns, length 30 cm and diameter 5 cm. The current in the solenoid changes at 200 A/s. Find the emf ε induced in the short coil.

N₁ = 1000N₂ = 50l = 30 cm⌀ = 5 cmdi/dt = 200 A/sμ₀ = 4π × 10⁻⁷ T·m/A

ε = mV

Answer key

1. I = 10 A
2. F = 0.01061 N
3. r = 0.7108 cm
4. r = 2.089 cm
5. ε = 6.25 V
6. ε = 82.25 mV

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