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 = 50 APr = ?B = 50 µT

A long straight wire carries 50 A. At what distance r from the wire is the magnetic flux density 50 µT?

I = 50 AB = 50 µTμ₀ = 4π × 10⁻⁷ T·m/A
r = cm
2.Easy
−v = 5 × 10⁶ m/sB = 0.2 T

An electron moves at 5 × 10⁶ m/s at an angle of 60° to a uniform magnetic field of 0.2 T. Find the magnitude of the magnetic force F on it.

|q| = 1.602 × 10⁻¹⁹ Cv = 5 × 10⁶ m/sB = 0.2 Tθ = 60°
F = fN
3.Medium
dB/dt > 0I = ?

A circular loop lies in a uniform magnetic field pointing out of the page. The field strength is increasing. Click the direction of the induced current in the loop as seen in the drawing.

B: out of the pagedB/dt > 0
  1. 1clockwise
  2. 2counterclockwise
4.Medium
nBA = 80 cm², N = 25B: 0.2 → 0.7 T

A coil of 25 turns, area 80 cm² and resistance 4 Ω forms a closed circuit. A uniform field perpendicular to the coil rises steadily from 0.2 T to 0.7 T in 250 ms. Find the average induced current I.

N = 25A = 80 cm²B: 0.2 T → 0.7 TΔt = 250 msR = 4 Ω
I = mA
5.Hard
I = 0.5 Al = 15 cmN = 500, ⌀ 3 cm

A long air-core solenoid has 500 turns, a length of 15 cm and a diameter of 3 cm. Find the energy W stored in its magnetic field when it carries 0.5 A.

N = 500l = 15 cm⌀ = 3 cmI = 0.5 Aμ₀ = 4π × 10⁻⁷ T·m/A
W = µJ
6.Hard
I = 4 Al = 10 cmN = 200, ⌀ 4 cm

A long air-core solenoid has 200 turns, a length of 10 cm and a diameter of 4 cm. Find the energy W stored in its magnetic field when it carries 4 A.

N = 200l = 10 cm⌀ = 4 cmI = 4 Aμ₀ = 4π × 10⁻⁷ T·m/A
W = mJ

Answer key

  1. 1. r = 20 cm
  2. 2. F = 138.7 fN
  3. 3. clockwise
  4. 4. I = 100 mA
  5. 5. W = 185.1 µJ
  6. 6. W = 5.053 mJ

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