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 25 turns and radius 12 cm carries a current of 1 A. Find the magnetic flux density B at its centre.

N = 25I = 1 AR = 12 cmμ₀ = 4π × 10⁻⁷ T·m/A

B = µT

2.Easy

A solenoid 30 cm long has 600 turns. Which current I gives a magnetic flux density of 7.54 mT inside it?

N = 600L = 30 cmB = 7.54 mTμ₀ = 4π × 10⁻⁷ T·m/A

I = A

3.Medium

Two long parallel wires 12 cm apart carry currents of 8 A and 5 A in the same direction. Find the force per metre of length F/L between them.

I₁ = 8 AI₂ = 5 Ad = 12 cmμ₀ = 4π × 10⁻⁷ T·m/A

F/L = µN/m

4.Medium

A coil of 250 turns, area 10 cm² and resistance 20 Ω forms a closed circuit. A uniform field perpendicular to the coil rises steadily from 0.05 T to 0.85 T in 500 ms. Find the average induced current I.

N = 250A = 10 cm²B: 0.05 T → 0.85 TΔt = 500 msR = 20 Ω

I = mA

5.Hard

An alpha particle starts from rest, is accelerated through a potential difference of 10000 V and then enters a uniform magnetic field of 0.1 T at right angles. Find the radius r of its path in the field.

m = 6.645 × 10⁻²⁷ kg|q| = 3.204 × 10⁻¹⁹ CV = 10000 VB = 0.1 T

r = cm

6.Hard

A long air-core solenoid has 200 turns, a length of 15 cm and a diameter of 5 cm. Find the energy W stored in its magnetic field when it carries 1.5 A.

N = 200l = 15 cm⌀ = 5 cmI = 1.5 Aμ₀ = 4π × 10⁻⁷ T·m/A

W = µJ

Answer key

1. B = 130.9 µT
2. I = 3 A
3. F/L = 66.67 µN/m
4. I = 20 mA
5. r = 20.37 cm
6. W = 740.2 µJ

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