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 a current of 25 A. Find the magnetic flux density B at point P, 20 cm from the wire.

I = 25 Ar = 20 cmμ₀ = 4π × 10⁻⁷ T·m/A

B = µT

2.Easy

A straight wire 80 cm long lies at 60° to a uniform magnetic field of 0.3 T. The magnetic force on it is 2.494 N. Find the current I.

B = 0.3 TF = 2.494 NL = 80 cmθ = 60°

I = A

3.Medium

A coil of 100 turns has an area of 50 cm². The coil sits in a uniform field of 0.5 T perpendicular to its plane, and the field is switched off in 10 ms. Find the average induced emf ε.

N = 100A = 50 cm²B = 0.5 TΔt = 10 ms

ε = V

4.Medium

Two long parallel wires 6 cm apart carry currents of 2 A and 10 A in opposite directions. Find the force per metre of length F/L between them.

I₁ = 2 AI₂ = 10 Ad = 6 cmμ₀ = 4π × 10⁻⁷ T·m/A

F/L = µN/m

5.Hard

A coil of 150 turns, 20 cm × 5 cm, rotates in a uniform field of 0.5 T about an axis perpendicular to the field. At what speed n (in revolutions per minute) must it turn to give an rms emf of 49.98 V?

N = 150A = 20 cm × 5 cmB = 0.5 TE_rms = 49.98 V

n = rpm

6.Hard

A proton starts from rest, is accelerated through a potential difference of 1000 V and then enters a uniform magnetic field of 0.2 T at right angles. Find the radius r of its path in the field.

m = 1.673 × 10⁻²⁷ kg|q| = 1.602 × 10⁻¹⁹ CV = 1000 VB = 0.2 T

r = cm

Answer key

1. B = 25 µT
2. I = 12 A
3. ε = 25 V
4. F/L = 66.67 µN/m
5. n = 900 rpm
6. r = 2.285 cm

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