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 = 5 AR = 10 cmB = ?N = 50

A flat circular coil of 50 turns and radius 10 cm carries a current of 5 A. Find the magnetic flux density B at its centre.

N = 50I = 5 AR = 10 cmμ₀ = 4π × 10⁻⁷ T·m/A
B = mT
2.Easy
B0.2 TI = ?90°L = 80 cm

A straight wire 80 cm long lies at 90° to a uniform magnetic field of 0.2 T. The magnetic force on it is 0.32 N. Find the current I.

B = 0.2 TF = 0.32 NL = 80 cmθ = 90°
I = A
3.Medium
dB/dt < 0I = ?

A circular loop lies in a uniform magnetic field pointing into the page. The field strength is decreasing. Click the direction of the induced current in the loop as seen in the drawing.

B: into the pagedB/dt < 0
  1. 1clockwise
  2. 2counterclockwise
4.Medium
12 A8 Ad = 5 cmP

Two long parallel wires 5 cm apart carry currents of 12 A and 8 A in opposite directions. Find the magnitude of the magnetic flux density B at point P, halfway between them.

I1 = 12 AI2 = 8 Ad = 5 cmμ₀ = 4π × 10⁻⁷ T·m/A
B = µT
5.Hard
L = 80 mH1 → 2 A

The current in an 80 mH inductor changes steadily from 1 A to 2 A in 5 ms. Find the magnitude of the self-induced emf ε.

L = 80 mH1 A → 2 AΔt = 5 ms
ε = V
6.Hard
I = 2 Al = 25 cmN = 400, ⌀ 2.5 cm

A long air-core solenoid has 400 turns, a length of 25 cm and a diameter of 2.5 cm. Find the energy W stored in its magnetic field when it carries 2 A.

N = 400l = 25 cm⌀ = 2.5 cmI = 2 Aμ₀ = 4π × 10⁻⁷ T·m/A
W = µJ

Answer key

  1. 1. B = 1.571 mT
  2. 2. I = 2 A
  3. 3. clockwise
  4. 4. B = 160 µT
  5. 5. ε = 16 V
  6. 6. W = 789.6 µJ

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