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 = 20 APr = 2.5 cmB = ?

A long straight wire carries a current of 20 A. Find the magnetic flux density B at point P, 2.5 cm from the wire.

I = 20 Ar = 2.5 cmμ₀ = 4π × 10⁻⁷ T·m/A
B = µT
2.Easy
I = ?Pr = 5 cmB = 32 µT

The magnetic flux density 5 cm from a long straight wire is 32 µT. Find the current I in the wire.

B = 32 µTr = 5 cmμ₀ = 4π × 10⁻⁷ T·m/A
I = A
3.Medium
nBA = 200 cm², N = 200B = 0.3 T

A coil of 200 turns has an area of 200 cm². The coil sits in a uniform field of 0.3 T perpendicular to its plane, and the field is switched off in 40 ms. Find the average induced emf ε.

N = 200A = 200 cm²B = 0.3 TΔt = 40 ms
ε = V
4.Medium
nBA = 20 cm², N = 250B = 0.3 T

A coil of 250 turns has an area of 20 cm². The coil is turned over (rotated through 180°) in a uniform field of 0.3 T, which is perpendicular to its plane, in 20 ms. Find the average induced emf ε.

N = 250A = 20 cm²B = 0.3 TΔt = 20 ms
ε = V
5.Hard
l = 25 cmN = 400, ⌀ 3 cm

A long air-core solenoid has 400 turns, a length of 25 cm and a diameter of 3 cm. Find its self-inductance L.

N = 400l = 25 cm⌀ = 3 cmμ₀ = 4π × 10⁻⁷ T·m/A
L = µH
6.Hard
N1​ = 500, l = 40 cmN2​ = 20M = ?

A short coil of 20 turns is wound tightly round the middle of a long solenoid of 500 turns, length 40 cm and diameter 5 cm. Find their mutual inductance M.

N1 = 500N2 = 20l = 40 cm⌀ = 5 cmμ₀ = 4π × 10⁻⁷ T·m/A
M = µH

Answer key

  1. 1. B = 160 µT
  2. 2. I = 8 A
  3. 3. ε = 30 V
  4. 4. ε = 15 V
  5. 5. L = 568.5 µH
  6. 6. M = 61.69 µH

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