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 T5 A90°L = 25 cm

A straight wire 25 cm long carries 5 A at an angle of 90° to a uniform magnetic field of 0.25 T. Find the magnitude of the force F on the wire.

B = 0.25 TI = 5 AL = 25 cmθ = 90°
F = N
2.Easy
I = 2.5 AR = 8 cmB = ?N = 10

A flat circular coil of 10 turns and radius 8 cm carries a current of 2.5 A. Find the magnetic flux density B at its centre.

N = 10I = 2.5 AR = 8 cmμ₀ = 4π × 10⁻⁷ T·m/A
B = µT
3.Medium
nBA = 100 cm², N = 250B = 0.3 T

A coil of 250 turns has an area of 100 cm². The coil is turned over (rotated through 180°) in a uniform field of 0.3 T, which is perpendicular to its plane, in 500 ms. Find the average induced emf ε.

N = 250A = 100 cm²B = 0.3 TΔt = 500 ms
ε = V
4.Medium
−vBF = ?

An electron moves up the page through a uniform magnetic field pointing into the page. Click the direction of the magnetic force on it.

v: up the pageB: into the page
  1. 1up the page
  2. 2to the right
  3. 3down the page
  4. 4to the left
5.Hard
Bn = ?10 cm × 5 cmN = 250B = 0.2 T

A coil of 250 turns, 10 cm × 5 cm, rotates in a uniform field of 0.2 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 66.64 V?

N = 250A = 10 cm × 5 cmB = 0.2 TErms = 66.64 V
n = rpm
6.Hard
L = 10 mH1 → 3 A

The current in a 10 mH inductor changes steadily from 1 A to 3 A in 50 ms. Find the magnitude of the self-induced emf ε.

L = 10 mH1 A → 3 AΔt = 50 ms
ε = V

Answer key

  1. 1. F = 0.3125 N
  2. 2. B = 196.3 µT
  3. 3. ε = 3 V
  4. 4. to the right
  5. 5. n = 3600 rpm
  6. 6. ε = 0.4 V

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