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 = 2 APr = 20 cmB = ?

A long straight wire carries a current of 2 A. Find the magnetic flux density B at point P, 20 cm from the wire.

I = 2 Ar = 20 cmμ₀ = 4π × 10⁻⁷ T·m/A
B = µT
2.Easy
B = 5.027 mTI = 1 AL = 25 cmN = ?

A solenoid 25 cm long carries 1 A. How many turns N must it have for a flux density of 5.027 mT inside?

I = 1 AL = 25 cmB = 5.027 mTμ₀ = 4π × 10⁻⁷ T·m/A
N =
3.Medium
nBA = 80 cm², N = 10B = 0.8 T

A coil of 10 turns has an area of 80 cm². The coil sits in a uniform field of 0.8 T perpendicular to its plane, and the field is switched off in 100 ms. Find the average induced emf ε.

N = 10A = 80 cm²B = 0.8 TΔt = 100 ms
ε = mV
4.Medium
R = 10 Ωv = 2.5 m/sL = 100 cmB = 0.5 T

A metal rod 100 cm long slides at 2.5 m/s along two rails in a uniform field of 0.5 T into the page. Find the induced emf ε between its ends.

B = 0.5 TL = 100 cmv = 2.5 m/s
ε = V
5.Hard
Bn = 1500 rpm12 cm × 5 cmN = 50B = 0.2 T

A coil of 50 turns, 12 cm × 5 cm, rotates at 1500 rpm in a uniform field of 0.2 T about an axis perpendicular to the field. Find the peak emf E0.

N = 50A = 12 cm × 5 cmB = 0.2 Tn = 1500 rpm
E0 = V
6.Hard
l = 10 cmN = 800, ⌀ 1 cm

A long air-core solenoid has 800 turns, a length of 10 cm and a diameter of 1 cm. Find its self-inductance L.

N = 800l = 10 cm⌀ = 1 cmμ₀ = 4π × 10⁻⁷ T·m/A
L = µH

Answer key

  1. 1. B = 2 µT
  2. 2. N = 1000
  3. 3. ε = 640 mV
  4. 4. ε = 1.25 V
  5. 5. E0 = 9.425 V
  6. 6. L = 631.7 µH

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