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 flat circular coil of 5 turns and radius 5 cm carries a current of 0.5 A. Find the magnetic flux density B at its centre.

N = 5I = 0.5 AR = 5 cmμ₀ = 4π × 10⁻⁷ T·m/A

B = µT

2.Easy

A flat circular coil of 5 turns and radius 12 cm carries a current of 3 A. Find the magnetic flux density B at its centre.

N = 5I = 3 AR = 12 cmμ₀ = 4π × 10⁻⁷ T·m/A

B = µT

3.Medium

A coil of 20 turns, area 25 cm² and resistance 8 Ω forms a closed circuit. A uniform field perpendicular to the coil rises steadily from 0 T to 0.5 T in 10 ms. Find the average induced current I.

N = 20A = 25 cm²B: 0 T → 0.5 TΔt = 10 msR = 8 Ω

I = mA

4.Medium

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

v: down the pageB: into the page

1up the page
2to the right
3down the page
4to the left

5.Hard

A long air-core solenoid has 100 turns, a length of 30 cm and a diameter of 2 cm. Find the energy W stored in its magnetic field when it carries 3 A.

N = 100l = 30 cm⌀ = 2 cmI = 3 Aμ₀ = 4π × 10⁻⁷ T·m/A

W = µJ

6.Hard

Two coils with self-inductances of 50 mH and 20 mH have a coupling coefficient of 0.8. The current in the first coil changes at 50 A/s. Find the emf ε induced in the second coil.

L₁ = 50 mHL₂ = 20 mHk = 0.8di/dt = 50 A/s

ε = V

Answer key

1. B = 31.42 µT
2. B = 78.54 µT
3. I = 312.5 mA
4. to the right
5. W = 59.22 µJ
6. ε = 1.265 V

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