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
B0.25 TI = ?90°L = 80 cm

A straight wire 80 cm long lies at 90° to a uniform magnetic field of 0.25 T. The magnetic force on it is 1.2 N. Find the current I.

B = 0.25 TF = 1.2 NL = 80 cmθ = 90°
I = A
2.Easy
B0.8 TI = ?90°L = 30 cm

A straight wire 30 cm long lies at 90° to a uniform magnetic field of 0.8 T. The magnetic force on it is 4.8 N. Find the current I.

B = 0.8 TF = 4.8 NL = 30 cmθ = 90°
I = A
3.Medium
nBA = 20 cm², N = 20B: 0.05 → 0.15 T

A coil of 20 turns has an area of 20 cm². A uniform field perpendicular to the coil rises steadily from 0.05 T to 0.15 T in 20 ms. Find the average induced emf ε.

N = 20A = 20 cm²B: 0.05 T → 0.15 TΔt = 20 ms
ε = mV
4.Medium
−v = 2 × 10⁶ m/sr = ?B = 10 mT

An electron moves at 2 × 10⁶ m/s perpendicular to a uniform magnetic field of 10 mT. Find the radius r of its circular path.

m = 9.109 × 10⁻³¹ kg|q| = 1.602 × 10⁻¹⁹ Cv = 2 × 10⁶ m/sB = 10 mT
r = cm
5.Hard
Bn = ?8 cm × 20 cmN = 150B = 0.4 T

A coil of 150 turns, 8 cm × 20 cm, rotates in a uniform field of 0.4 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 128 V?

N = 150A = 8 cm × 20 cmB = 0.4 TErms = 128 V
n = rpm
6.Hard
I = 3 Al = 20 cmN = 300, ⌀ 4 cm

A long air-core solenoid has 300 turns, a length of 20 cm and a diameter of 4 cm. Find the energy W stored in its magnetic field when it carries 3 A.

N = 300l = 20 cm⌀ = 4 cmI = 3 Aμ₀ = 4π × 10⁻⁷ T·m/A
W = mJ

Answer key

  1. 1. I = 6 A
  2. 2. I = 20 A
  3. 3. ε = 200 mV
  4. 4. r = 0.1137 cm
  5. 5. n = 1801 rpm
  6. 6. W = 3.198 mJ

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