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 long straight wire carries 2 A. At what distance r from the wire is the magnetic flux density 2 µT?

I = 2 AB = 2 µTμ₀ = 4π × 10⁻⁷ T·m/A

r = cm

2.Easy

The magnetic flux density 12 cm from a long straight wire is 20 µT. Find the current I in the wire.

B = 20 µTr = 12 cmμ₀ = 4π × 10⁻⁷ T·m/A

I = A

3.Medium

An alpha particle moves on a circle in a uniform magnetic field of 0.4 T. Find the time T it takes for one revolution.

m = 6.645 × 10⁻²⁷ kg|q| = 3.204 × 10⁻¹⁹ CB = 0.4 T

T = ns

4.Medium

A coil of 250 turns, area 100 cm² and resistance 5 Ω forms a closed circuit. A uniform field perpendicular to the coil rises steadily from 0 T to 0.4 T in 500 ms. Find the average induced current I.

N = 250A = 100 cm²B: 0 T → 0.4 TΔt = 500 msR = 5 Ω

I = mA

5.Hard

A short coil of 100 turns is wound tightly round the middle of a long solenoid of 500 turns, length 20 cm and diameter 5 cm. The current in the solenoid changes at 1000 A/s. Find the emf ε induced in the short coil.

N₁ = 500N₂ = 100l = 20 cm⌀ = 5 cmdi/dt = 1000 A/sμ₀ = 4π × 10⁻⁷ T·m/A

ε = mV

6.Hard

The current in a 50 mH inductor changes steadily from 3 A to 2 A in 50 ms. Find the magnitude of the self-induced emf ε.

L = 50 mH3 A → 2 AΔt = 50 ms

ε = V

Answer key

1. r = 20 cm
2. I = 12 A
3. T = 325.8 ns
4. I = 400 mA
5. ε = 616.9 mV
6. ε = 1 V

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