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 flat circular coil of 50 turns and radius 15 cm carries a current of 2.5 A. Find the magnetic flux density B at its centre.

N = 50I = 2.5 AR = 15 cmμ₀ = 4π × 10⁻⁷ T·m/A

B = µT

2.Easy

A straight wire 30 cm long lies at 30° to a uniform magnetic field of 0.05 T. The magnetic force on it is 0.0225 N. Find the current I.

B = 0.05 TF = 0.0225 NL = 30 cmθ = 30°

I = A

3.Medium

Two long parallel wires 10 cm apart carry currents of 10 A and 8 A in opposite directions. Find the force per metre of length F/L between them.

I₁ = 10 AI₂ = 8 Ad = 10 cmμ₀ = 4π × 10⁻⁷ T·m/A

F/L = µN/m

4.Medium

A coil of 25 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 50 ms. Find the average induced emf ε.

N = 25A = 200 cm²B = 0.2 TΔt = 50 ms

ε = V

5.Hard

The current in an 80 mH inductor changes steadily from 0.5 A to 3.5 A in 20 ms. Find the magnitude of the self-induced emf ε.

L = 80 mH0.5 A → 3.5 AΔt = 20 ms

ε = V

6.Hard

A coil of 250 turns, 8 cm × 15 cm, rotates in a uniform field of 0.2 T about an axis perpendicular to the field. At what speed n (in revolutions per minute) must it turn to give an rms emf of 53.31 V?

N = 250A = 8 cm × 15 cmB = 0.2 TE_rms = 53.31 V

n = rpm

Answer key

1. B = 523.6 µT
2. I = 3 A
3. F/L = 160 µN/m
4. ε = 2 V
5. ε = 12 V
6. n = 1200 rpm

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