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
B1.2 T3 A90°L = 15 cm

A straight wire 15 cm long carries 3 A at an angle of 90° to a uniform magnetic field of 1.2 T. Find the magnitude of the force F on the wire.

B = 1.2 TI = 3 AL = 15 cmθ = 90°
F = N
2.Easy
I = 5 AR = 3 cmB = ?N = 25

A flat circular coil of 25 turns and radius 3 cm carries a current of 5 A. Find the magnetic flux density B at its centre.

N = 25I = 5 AR = 3 cmμ₀ = 4π × 10⁻⁷ T·m/A
B = mT
3.Medium
nBA = 150 cm², N = 100B: 0 → 0.5 T

A coil of 100 turns, area 150 cm² and resistance 10 Ω forms a closed circuit. A uniform field perpendicular to the coil rises steadily from 0 T to 0.5 T in 10 ms. Find the average induced current I.

N = 100A = 150 cm²B: 0 T → 0.5 TΔt = 10 msR = 10 Ω
I = A
4.Medium
nBA = 25 cm², N = 20B = 0.5 T

A coil of 20 turns has an area of 25 cm². The coil sits in a uniform field of 0.5 T perpendicular to its plane, and the field is switched off in 500 ms. Find the average induced emf ε.

N = 20A = 25 cm²B = 0.5 TΔt = 500 ms
ε = mV
5.Hard
Bn = ?8 cm × 25 cmN = 100B = 0.1 T

A coil of 100 turns, 8 cm × 25 cm, rotates in a uniform field of 0.1 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 22.21 V?

N = 100A = 8 cm × 25 cmB = 0.1 TErms = 22.21 V
n = rpm
6.Hard
V = 5000 VB = 0.8 Tr = ?

A proton starts from rest, is accelerated through a potential difference of 5000 V and then enters a uniform magnetic field of 0.8 T at right angles. Find the radius r of its path in the field.

m = 1.673 × 10⁻²⁷ kg|q| = 1.602 × 10⁻¹⁹ CV = 5000 VB = 0.8 T
r = cm

Answer key

  1. 1. F = 0.54 N
  2. 2. B = 2.618 mT
  3. 3. I = 7.5 A
  4. 4. ε = 50 mV
  5. 5. n = 1500 rpm
  6. 6. r = 1.277 cm

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