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

A solenoid 40 cm long has 600 turns. Which current I gives a magnetic flux density of 0.9425 mT inside it?

N = 600L = 40 cmB = 0.9425 mTμ₀ = 4π × 10⁻⁷ T·m/A

I = A

2.Easy

A flat circular coil of 20 turns and radius 15 cm carries a current of 4 A. Find the magnetic flux density B at its centre.

N = 20I = 4 AR = 15 cmμ₀ = 4π × 10⁻⁷ T·m/A

B = µT

3.Medium

A metal rod 80 cm long slides at 10 m/s along two rails in a uniform field of 0.5 T into the page. The rails are joined by a resistor of 1 Ω; the rod and rails have negligible resistance. Find the force F needed to keep the rod moving at constant speed (no friction).

B = 0.5 TL = 80 cmv = 10 m/sR = 1 Ω

F = N

4.Medium

A coil of 250 turns has an area of 10 cm². The coil sits in a uniform field of 0.1 T perpendicular to its plane, and the field is switched off in 20 ms. Find the average induced emf ε.

N = 250A = 10 cm²B = 0.1 TΔt = 20 ms

ε = V

5.Hard

A coil of 50 turns, 8 cm × 10 cm, rotates at 1800 rpm in a uniform field of 0.25 T about an axis perpendicular to the field. Find the rms value E_rms of the emf.

N = 50A = 8 cm × 10 cmB = 0.25 Tn = 1800 rpm

E_rms = V

6.Hard

A coil of 200 turns, 5 cm × 15 cm, rotates at 3600 rpm in a uniform field of 0.3 T about an axis perpendicular to the field. Find the peak emf E₀.

N = 200A = 5 cm × 15 cmB = 0.3 Tn = 3600 rpm

E₀ = V

Answer key

1. I = 0.5 A
2. B = 335.1 µT
3. F = 1.6 N
4. ε = 1.25 V
5. E_rms = 13.33 V
6. E₀ = 169.6 V

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