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

An electron moves at 5 × 10⁶ m/s perpendicular to a uniform magnetic field of 0.5 T. Find the magnitude of the magnetic force F on it.

|q| = 1.602 × 10⁻¹⁹ Cv = 5 × 10⁶ m/sB = 0.5 Tθ = 90°

F = fN

2.Easy

A solenoid 25 cm long carries 1 A. How many turns N must it have for a flux density of 1.257 mT inside?

I = 1 AL = 25 cmB = 1.257 mTμ₀ = 4π × 10⁻⁷ T·m/A

N =

3.Medium

Two long parallel wires 3 cm apart carry currents of 12 A and 25 A in the same direction. Find the force per metre of length F/L between them.

I₁ = 12 AI₂ = 25 Ad = 3 cmμ₀ = 4π × 10⁻⁷ T·m/A

F/L = µN/m

4.Medium

A coil of 50 turns, area 40 cm² and resistance 20 Ω forms a closed circuit. A uniform field perpendicular to the coil rises steadily from 0.05 T to 0.35 T in 500 ms. Find the average induced current I.

N = 50A = 40 cm²B: 0.05 T → 0.35 TΔt = 500 msR = 20 Ω

I = mA

5.Hard

A long air-core solenoid has 2000 turns, a length of 15 cm and a diameter of 3 cm. Find the energy W stored in its magnetic field when it carries 0.5 A.

N = 2000l = 15 cm⌀ = 3 cmI = 0.5 Aμ₀ = 4π × 10⁻⁷ T·m/A

W = mJ

6.Hard

A coil of 20 turns, 12 cm × 15 cm, rotates at 3000 rpm in a uniform field of 0.3 T about an axis perpendicular to the field. Find the rms value E_rms of the emf.

N = 20A = 12 cm × 15 cmB = 0.3 Tn = 3000 rpm

E_rms = V

Answer key

1. F = 400.5 fN
2. N = 250.1
3. F/L = 2000 µN/m
4. I = 6 mA
5. W = 2.961 mJ
6. E_rms = 23.99 V

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