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 5 turns and radius 3 cm carries a current of 3 A. Find the magnetic flux density B at its centre.

N = 5I = 3 AR = 3 cmμ₀ = 4π × 10⁻⁷ T·m/A

B = µT

2.Easy

A straight wire 100 cm long carries 12 A at an angle of 30° to a uniform magnetic field of 0.05 T. Find the magnitude of the force F on the wire.

B = 0.05 TI = 12 AL = 100 cmθ = 30°

F = N

3.Medium

A coil of 500 turns, area 40 cm² and resistance 2 Ω forms a closed circuit. A uniform field perpendicular to the coil rises steadily from 0.1 T to 0.2 T in 500 ms. Find the average induced current I.

N = 500A = 40 cm²B: 0.1 T → 0.2 TΔt = 500 msR = 2 Ω

I = mA

4.Medium

A proton moves at 5 × 10⁵ m/s perpendicular to a uniform magnetic field of 0.2 T. Find the radius r of its circular path.

m = 1.673 × 10⁻²⁷ kg|q| = 1.602 × 10⁻¹⁹ Cv = 5 × 10⁵ m/sB = 0.2 T

r = cm

5.Hard

A long air-core solenoid has 500 turns, a length of 20 cm and a diameter of 1.5 cm. Find the energy W stored in its magnetic field when it carries 4 A.

N = 500l = 20 cm⌀ = 1.5 cmI = 4 Aμ₀ = 4π × 10⁻⁷ T·m/A

W = mJ

6.Hard

In a velocity selector, crossed fields E = 2 × 10⁴ V/m and B = 0.2 T let only ions of one speed pass straight through. Find that speed v.

E = 2 × 10⁴ V/mB₁ = 0.2 T

v = m/s

Answer key

1. B = 314.2 µT
2. F = 0.3 N
3. I = 200 mA
4. r = 2.611 cm
5. W = 2.221 mJ
6. v = 100000 m/s

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