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 T6 A60°L = 80 cm

A straight wire 80 cm long carries 6 A at an angle of 60° to a uniform magnetic field of 0.25 T. Find the magnitude of the force F on the wire.

B = 0.25 TI = 6 AL = 80 cmθ = 60°
F = N
2.Easy
I = 5 AR = 4 cmB = ?N = 25

A flat circular coil of 25 turns and radius 4 cm carries a current of 5 A. Find the magnetic flux density B at its centre.

N = 25I = 5 AR = 4 cmμ₀ = 4π × 10⁻⁷ T·m/A
B = mT
3.Medium
R = 1 Ωv = 4 m/sL = 60 cmB = 0.5 T

A metal rod 60 cm long slides at 4 m/s along two rails in a uniform field of 0.5 T into the page. The rails are joined by a resistor of 1 Ω; the rod and rails have negligible resistance. Find the current I.

B = 0.5 TL = 60 cmv = 4 m/sR = 1 Ω
I = A
4.Medium
nBA = 10 cm², N = 500B = 0.4 T

A coil of 500 turns has an area of 10 cm². The coil sits in a uniform field of 0.4 T perpendicular to its plane, and the field is switched off in 10 ms. Find the average induced emf ε.

N = 500A = 10 cm²B = 0.4 TΔt = 10 ms
ε = V
5.Hard
L = 10 mH2 → 1 A

The current in a 10 mH inductor changes steadily from 2 A to 1 A in 20 ms. Find the magnitude of the self-induced emf ε.

L = 10 mH2 A → 1 AΔt = 20 ms
ε = V
6.Hard
l = 40 cmN = 1000, ⌀ 1 cm

A long air-core solenoid has 1000 turns, a length of 40 cm and a diameter of 1 cm. Find its self-inductance L.

N = 1000l = 40 cm⌀ = 1 cmμ₀ = 4π × 10⁻⁷ T·m/A
L = µH

Answer key

  1. 1. F = 1.039 N
  2. 2. B = 1.963 mT
  3. 3. I = 1.2 A
  4. 4. ε = 20 V
  5. 5. ε = 0.5 V
  6. 6. L = 246.7 µH

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