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 = 4 AR = 5 cmB = ?N = 50

A flat circular coil of 50 turns and radius 5 cm carries a current of 4 A. Find the magnetic flux density B at its centre.

N = 50I = 4 AR = 5 cmμ₀ = 4π × 10⁻⁷ T·m/A
B = mT
2.Easy
B = 6.283 mTI = 3 AL = 12 cmN = ?

A solenoid 12 cm long carries 3 A. How many turns N must it have for a flux density of 6.283 mT inside?

I = 3 AL = 12 cmB = 6.283 mTμ₀ = 4π × 10⁻⁷ T·m/A
N =
3.Medium
+vBF = ?

A proton moves to the right through a uniform magnetic field pointing into the page. Click the direction of the magnetic force on it.

v: to the rightB: into the page
  1. 1up the page
  2. 2to the right
  3. 3down the page
  4. 4to the left
4.Medium
nBA = 80 cm², N = 500B: 0 → 0.6 T

A coil of 500 turns has an area of 80 cm². A uniform field perpendicular to the coil rises steadily from 0 T to 0.6 T in 100 ms. Find the average induced emf ε.

N = 500A = 80 cm²B: 0 T → 0.6 TΔt = 100 ms
ε = V
5.Hard
I = 1 Al = 30 cmN = 500, ⌀ 2 cm

A long air-core solenoid has 500 turns, a length of 30 cm and a diameter of 2 cm. Find the energy W stored in its magnetic field when it carries 1 A.

N = 500l = 30 cm⌀ = 2 cmI = 1 Aμ₀ = 4π × 10⁻⁷ T·m/A
W = µJ
6.Hard
L = 25 mH1 → 6 A

The current in a 25 mH inductor changes steadily from 1 A to 6 A in 20 ms. Find the magnitude of the self-induced emf ε.

L = 25 mH1 A → 6 AΔt = 20 ms
ε = V

Answer key

  1. 1. B = 2.513 mT
  2. 2. N = 200
  3. 3. up the page
  4. 4. ε = 24 V
  5. 5. W = 164.5 µJ
  6. 6. ε = 6.25 V

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