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 15 cm long carries 1 A. How many turns N must it have for a flux density of 5.027 mT inside?

I = 1 AL = 15 cmB = 5.027 mTμ₀ = 4π × 10⁻⁷ T·m/A

N =

2.Easy

A straight wire 15 cm long carries 4 A at an angle of 30° to a uniform magnetic field of 0.4 T. Find the magnitude of the force F on the wire.

B = 0.4 TI = 4 AL = 15 cmθ = 30°

F = N

3.Medium

A metal rod 50 cm long slides at 2.5 m/s along two rails in a uniform field of 0.5 T into the page. The rails are joined by a resistor of 10 Ω; the rod and rails have negligible resistance. Find the force F needed to keep the rod moving at constant speed (no friction).

B = 0.5 TL = 50 cmv = 2.5 m/sR = 10 Ω

F = mN

4.Medium

A coil of 250 turns has an area of 25 cm². A uniform field perpendicular to the coil rises steadily from 0.2 T to 0.4 T in 10 ms. Find the average induced emf ε.

N = 250A = 25 cm²B: 0.2 T → 0.4 TΔt = 10 ms

ε = V

5.Hard

A long air-core solenoid has 200 turns, a length of 30 cm and a diameter of 3 cm. Find its self-inductance L.

N = 200l = 30 cm⌀ = 3 cmμ₀ = 4π × 10⁻⁷ T·m/A

L = µH

6.Hard

The current in a 5 mH inductor changes steadily from 1 A to 5 A in 50 ms. Find the magnitude of the self-induced emf ε.

L = 5 mH1 A → 5 AΔt = 50 ms

ε = V

Answer key

1. N = 600.1
2. F = 0.12 N
3. F = 15.63 mN
4. ε = 12.5 V
5. L = 118.4 µH
6. ε = 0.4 V

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