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 = 83.33 µT

A long straight wire carries 50 A. At what distance r from the wire is the magnetic flux density 83.33 µT?

I = 50 AB = 83.33 µTμ₀ = 4π × 10⁻⁷ T·m/A
r = cm
2.Easy
I = 3 AR = 5 cmB = ?N = 20

A flat circular coil of 20 turns and radius 5 cm carries a current of 3 A. Find the magnetic flux density B at its centre.

N = 20I = 3 AR = 5 cmμ₀ = 4π × 10⁻⁷ T·m/A
B = µT
3.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
4.Medium
nBA = 50 cm², N = 200B = 0.4 T

A coil of 200 turns has an area of 50 cm². The coil is turned over (rotated through 180°) in a uniform field of 0.4 T, which is perpendicular to its plane, in 250 ms. Find the average induced emf ε.

N = 200A = 50 cm²B = 0.4 TΔt = 250 ms
ε = V
5.Hard
L1​ = 50 mH500 A/sL2​ = 10 mHk = 0.8ε = ?

Two coils with self-inductances of 50 mH and 10 mH have a coupling coefficient of 0.8. The current in the first coil changes at 500 A/s. Find the emf ε induced in the second coil.

L1 = 50 mHL2 = 10 mHk = 0.8di/dt = 500 A/s
ε = V
6.Hard
L = 25 mH1 → 0 A

The current in a 25 mH inductor changes steadily from 1 A to 0 A in 20 ms. Find the magnitude of the self-induced emf ε.

L = 25 mH1 A → 0 AΔt = 20 ms
ε = V

Answer key

  1. 1. r = 12 cm
  2. 2. B = 754 µT
  3. 3. counterclockwise
  4. 4. ε = 3.2 V
  5. 5. ε = 8.944 V
  6. 6. ε = 1.25 V

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