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 = 0.5 AR = 4 cmB = ?N = 25

A flat circular coil of 25 turns and radius 4 cm carries a current of 0.5 A. Find the magnetic flux density B at its centre.

N = 25I = 0.5 AR = 4 cmμ₀ = 4π × 10⁻⁷ T·m/A
B = µT
2.Easy
I = 8 APr = ?B = 26.67 µT

A long straight wire carries 8 A. At what distance r from the wire is the magnetic flux density 26.67 µT?

I = 8 AB = 26.67 µTμ₀ = 4π × 10⁻⁷ T·m/A
r = cm
3.Medium
R = 2 Ωv = 5 m/sL = 30 cmB = 1 T

A metal rod 30 cm long slides at 5 m/s along two rails in a uniform field of 1 T into the page. The rails are joined by a resistor of 2 Ω; the rod and rails have negligible resistance. Find the power P dissipated in the resistor.

B = 1 TL = 30 cmv = 5 m/sR = 2 Ω
P = W
4.Medium
dB/dt < 0I = ?

A circular loop lies in a uniform magnetic field pointing out of the page. The field strength is decreasing. 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
5.Hard
L = 100 mH2 → 3 A

The current in a 100 mH inductor changes steadily from 2 A to 3 A in 1 ms. Find the magnitude of the self-induced emf ε.

L = 100 mH2 A → 3 AΔt = 1 ms
ε = V
6.Hard
L = 100 mH0 → 2 A

The current in a 100 mH inductor changes steadily from 0 A to 2 A in 5 ms. Find the magnitude of the self-induced emf ε.

L = 100 mH0 A → 2 AΔt = 5 ms
ε = V

Answer key

  1. 1. B = 196.3 µT
  2. 2. r = 5.999 cm
  3. 3. P = 1.125 W
  4. 4. counterclockwise
  5. 5. ε = 100 V
  6. 6. ε = 40 V

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