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
B0.4 T1 A60°L = 10 cm

A straight wire 10 cm long carries 1 A at an angle of 60° to a uniform magnetic field of 0.4 T. Find the magnitude of the force F on the wire.

B = 0.4 TI = 1 AL = 10 cmθ = 60°
F = N
2.Easy
B1.2 TI = ?90°L = 100 cm

A straight wire 100 cm long lies at 90° to a uniform magnetic field of 1.2 T. The magnetic force on it is 7.2 N. Find the current I.

B = 1.2 TF = 7.2 NL = 100 cmθ = 90°
I = A
3.Medium
5 A10 Ad = 10 cmP

Two long parallel wires 10 cm apart carry currents of 5 A and 10 A in the same direction. Find the magnitude of the magnetic flux density B at point P, halfway between them.

I1 = 5 AI2 = 10 Ad = 10 cmμ₀ = 4π × 10⁻⁷ T·m/A
B = µT
4.Medium
nBA = 25 cm², N = 250B: 0.1 → 0.7 T

A coil of 250 turns has an area of 25 cm². A uniform field perpendicular to the coil rises steadily from 0.1 T to 0.7 T in 250 ms. Find the average induced emf ε.

N = 250A = 25 cm²B: 0.1 T → 0.7 TΔt = 250 ms
ε = V
5.Hard
Bn = 1500 rpm20 cm × 20 cmN = 500B = 0.1 T

A coil of 500 turns, 20 cm × 20 cm, rotates at 1500 rpm in a uniform field of 0.1 T about an axis perpendicular to the field. Find the peak emf E0.

N = 500A = 20 cm × 20 cmB = 0.1 Tn = 1500 rpm
E0 = V
6.Hard
L = 40 mH3 → 0 A

The current in a 40 mH inductor changes steadily from 3 A to 0 A in 10 ms. Find the magnitude of the self-induced emf ε.

L = 40 mH3 A → 0 AΔt = 10 ms
ε = V

Answer key

  1. 1. F = 0.03464 N
  2. 2. I = 6 A
  3. 3. B = 20 µT
  4. 4. ε = 1.5 V
  5. 5. E0 = 314.2 V
  6. 6. ε = 12 V

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