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 = ?Pr = 2 cmB = 80 µT

The magnetic flux density 2 cm from a long straight wire is 80 µT. Find the current I in the wire.

B = 80 µTr = 2 cmμ₀ = 4π × 10⁻⁷ T·m/A
I = A
2.Easy
I = 12 APr = 10 cmB = ?

A long straight wire carries a current of 12 A. Find the magnetic flux density B at point P, 10 cm from the wire.

I = 12 Ar = 10 cmμ₀ = 4π × 10⁻⁷ T·m/A
B = µT
3.Medium
2 A10 Ad = 15 cm

Two long parallel wires 15 cm apart carry currents of 2 A and 10 A in the same direction. Find the force per metre of length F/L between them.

I1 = 2 AI2 = 10 Ad = 15 cmμ₀ = 4π × 10⁻⁷ T·m/A
F/L = µN/m
4.Medium
nBA = 50 cm², N = 20B = 0.1 T

A coil of 20 turns has an area of 50 cm². The coil sits in a uniform field of 0.1 T perpendicular to its plane, and the field is switched off in 250 ms. Find the average induced emf ε.

N = 20A = 50 cm²B = 0.1 TΔt = 250 ms
ε = mV
5.Hard
l = 40 cmN = 2000, ⌀ 2 cm

A long air-core solenoid has 2000 turns, a length of 40 cm and a diameter of 2 cm. Find its self-inductance L.

N = 2000l = 40 cm⌀ = 2 cmμ₀ = 4π × 10⁻⁷ T·m/A
L = mH
6.Hard
I = 1.5 Al = 40 cmN = 400, ⌀ 1.5 cm

A long air-core solenoid has 400 turns, a length of 40 cm and a diameter of 1.5 cm. Find the energy W stored in its magnetic field when it carries 1.5 A.

N = 400l = 40 cm⌀ = 1.5 cmI = 1.5 Aμ₀ = 4π × 10⁻⁷ T·m/A
W = µJ

Answer key

  1. 1. I = 8 A
  2. 2. B = 24 µT
  3. 3. F/L = 26.67 µN/m
  4. 4. ε = 40 mV
  5. 5. L = 3.948 mH
  6. 6. W = 99.93 µJ

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