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 = 8 cmB = ?

A single circular loop of wire with radius 8 cm carries a current of 5 A. Find the magnetic flux density B at its centre.

N = 1I = 5 AR = 8 cmμ₀ = 4π × 10⁻⁷ T·m/A
B = µT
2.Easy
I = 2 AR = 5 cmB = ?N = 20

A flat circular coil of 20 turns and radius 5 cm carries a current of 2 A. Find the magnetic flux density B at its centre.

N = 20I = 2 AR = 5 cmμ₀ = 4π × 10⁻⁷ T·m/A
B = µT
3.Medium
−v = 6 × 10⁶ m/sB = 2.5 mT

An electron moves on a circle in a uniform magnetic field of 2.5 mT. Find the time T it takes for one revolution.

m = 9.109 × 10⁻³¹ kg|q| = 1.602 × 10⁻¹⁹ CB = 2.5 mT
T = ns
4.Medium
IBF = ?

A wire carries a current up the page through a uniform magnetic field pointing out of the page. Click the direction of the magnetic force on the wire.

I: up the pageB: out of the page
  1. 1up the page
  2. 2to the right
  3. 3down the page
  4. 4to the left
5.Hard
Bn = ?8 cm × 20 cmN = 250B = 0.2 T

A coil of 250 turns, 8 cm × 20 cm, rotates in a uniform field of 0.2 T about an axis perpendicular to the field. At what speed n (in revolutions per minute) must it turn to give an rms emf of 177.7 V?

N = 250A = 8 cm × 20 cmB = 0.2 TErms = 177.7 V
n = rpm
6.Hard
L = 200 mH0.5 → 1 A

The current in a 200 mH inductor changes steadily from 0.5 A to 1 A in 1 ms. Find the magnitude of the self-induced emf ε.

L = 200 mH0.5 A → 1 AΔt = 1 ms
ε = V

Answer key

  1. 1. B = 39.27 µT
  2. 2. B = 502.7 µT
  3. 3. T = 14.29 ns
  4. 4. to the right
  5. 5. n = 3000 rpm
  6. 6. ε = 100 V

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