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 = 0.5 AR = 4 cmB = ?N = 10

A flat circular coil of 10 turns and radius 4 cm carries a current of 0.5 A. Find the magnetic flux density B at its centre.

N = 10I = 0.5 AR = 4 cmμ₀ = 4π × 10⁻⁷ T·m/A
B = µT
2.Easy
−v = 5 × 10⁶ m/sB = 0.02 T

An electron moves at 5 × 10⁶ m/s at an angle of 60° to a uniform magnetic field of 0.02 T. Find the magnitude of the magnetic force F on it.

|q| = 1.602 × 10⁻¹⁹ Cv = 5 × 10⁶ m/sB = 0.02 Tθ = 60°
F = fN
3.Medium
+v = 6 × 10⁶ m/sr = 8.296 cmB = ?

An alpha particle moving at 6 × 10⁶ m/s enters a uniform magnetic field at right angles and moves on a circle of radius 8.296 cm. Find the magnetic flux density B.

m = 6.645 × 10⁻²⁷ kg|q| = 3.204 × 10⁻¹⁹ Cv = 6 × 10⁶ m/sr = 8.296 cm
B = T
4.Medium
R = 4 Ωv = 1 m/sL = 60 cmB = 0.1 T

A metal rod 60 cm long slides at 1 m/s along two rails in a uniform field of 0.1 T into the page. The rails are joined by a resistor of 4 Ω; the rod and rails have negligible resistance. Find the force F needed to keep the rod moving at constant speed (no friction).

B = 0.1 TL = 60 cmv = 1 m/sR = 4 Ω
F = mN
5.Hard
L = 20 mH1 → 1.5 A

The current in a 20 mH inductor changes steadily from 1 A to 1.5 A in 20 ms. Find the magnitude of the self-induced emf ε.

L = 20 mH1 A → 1.5 AΔt = 20 ms
ε = V
6.Hard
l = 20 cmN = 200, ⌀ 4 cm

A long air-core solenoid has 200 turns, a length of 20 cm and a diameter of 4 cm. Find its self-inductance L.

N = 200l = 20 cm⌀ = 4 cmμ₀ = 4π × 10⁻⁷ T·m/A
L = µH

Answer key

  1. 1. B = 78.54 µT
  2. 2. F = 13.87 fN
  3. 3. B = 1.5 T
  4. 4. F = 0.9 mN
  5. 5. ε = 0.5 V
  6. 6. L = 315.8 µH

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