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
I = 30 APr = ?B = 150 µT

A long straight wire carries 30 A. At what distance r from the wire is the magnetic flux density 150 µT?

I = 30 AB = 150 µTμ₀ = 4π × 10⁻⁷ T·m/A
r = cm
2.Easy
I = 4 APr = 5 cmB = ?

A long straight wire carries a current of 4 A. Find the magnetic flux density B at point P, 5 cm from the wire.

I = 4 Ar = 5 cmμ₀ = 4π × 10⁻⁷ T·m/A
B = µT
3.Medium
+v = 3 × 10⁶ m/sB = 0.1 T

An alpha particle moves on a circle in a uniform magnetic field of 0.1 T. Find the time T it takes for one revolution.

m = 6.645 × 10⁻²⁷ kg|q| = 3.204 × 10⁻¹⁹ CB = 0.1 T
T = ns
4.Medium
nBA = 50 cm², N = 25B = 0.4 T

A coil of 25 turns has an area of 50 cm². The coil sits in a uniform field of 0.4 T perpendicular to its plane, and the field is switched off in 500 ms. Find the average induced emf ε.

N = 25A = 50 cm²B = 0.4 TΔt = 500 ms
ε = mV
5.Hard
L = 5 mH0 → 0.5 A

The current in a 5 mH inductor changes steadily from 0 A to 0.5 A in 1 ms. Find the magnitude of the self-induced emf ε.

L = 5 mH0 A → 0.5 AΔt = 1 ms
ε = V
6.Hard
Bn = 3600 rpm12 cm × 15 cmN = 150B = 0.5 T

A coil of 150 turns, 12 cm × 15 cm, rotates at 3600 rpm in a uniform field of 0.5 T about an axis perpendicular to the field. Find the peak emf E0.

N = 150A = 12 cm × 15 cmB = 0.5 Tn = 3600 rpm
E0 = V

Answer key

  1. 1. r = 4 cm
  2. 2. B = 16 µT
  3. 3. T = 1303 ns
  4. 4. ε = 100 mV
  5. 5. ε = 2.5 V
  6. 6. E0 = 508.9 V

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