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 rectangular loop of 8 cm by 10 cm lies in a uniform magnetic field of 0.2 T. The field lines make an angle of 30° with the plane of the loop. Find the magnetic flux Φ through the loop.

B = 0.2 TA = 8 cm × 10 cm30° to the plane

Φ = mWb

2.Easy

A straight wire 40 cm long carries 15 A at an angle of 90° to a uniform magnetic field of 0.8 T. Find the magnitude of the force F on the wire.

B = 0.8 TI = 15 AL = 40 cmθ = 90°

F = N

3.Medium

A metal rod 20 cm long slides at 10 m/s along two rails in a uniform field of 0.25 T into the page. The rails are joined by a resistor of 4 Ω; the rod and rails have negligible resistance. Find the current I.

B = 0.25 TL = 20 cmv = 10 m/sR = 4 Ω

I = mA

4.Medium

Two long parallel wires 15 cm apart carry currents of 2 A and 25 A in the same direction. Find the force per metre of length F/L between them.

I₁ = 2 AI₂ = 25 Ad = 15 cmμ₀ = 4π × 10⁻⁷ T·m/A

F/L = µN/m

5.Hard

A long air-core solenoid has 100 turns, a length of 25 cm and a diameter of 4 cm. Find its self-inductance L.

N = 100l = 25 cm⌀ = 4 cmμ₀ = 4π × 10⁻⁷ T·m/A

L = µH

6.Hard

The current in a 200 mH inductor changes steadily from 2.5 A to 2 A in 50 ms. Find the magnitude of the self-induced emf ε.

L = 200 mH2.5 A → 2 AΔt = 50 ms

ε = V

Answer key

1. Φ = 0.8 mWb
2. F = 4.8 N
3. I = 125 mA
4. F/L = 66.67 µN/m
5. L = 63.17 µH
6. ε = 2 V

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