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 long straight wire carries a current of 12 A. Find the magnetic flux density B at point P, 2 cm from the wire.

I = 12 Ar = 2 cmμ₀ = 4π × 10⁻⁷ T·m/A

B = µT

2.Easy

A long straight wire carries 25 A. At what distance r from the wire is the magnetic flux density 200 µT?

I = 25 AB = 200 µTμ₀ = 4π × 10⁻⁷ T·m/A

r = cm

3.Medium

A coil of 50 turns has an area of 80 cm². The coil is turned over (rotated through 180°) in a uniform field of 0.3 T, which is perpendicular to its plane, in 250 ms. Find the average induced emf ε.

N = 50A = 80 cm²B = 0.3 TΔt = 250 ms

ε = mV

4.Medium

An alpha particle moves on a circle in a uniform magnetic field of 1 T. Find the time T it takes for one revolution.

m = 6.645 × 10⁻²⁷ kg|q| = 3.204 × 10⁻¹⁹ CB = 1 T

T = ns

5.Hard

A proton starts from rest, is accelerated through a potential difference of 2500 V and then enters a uniform magnetic field of 0.8 T at right angles. Find the radius r of its path in the field.

m = 1.673 × 10⁻²⁷ kg|q| = 1.602 × 10⁻¹⁹ CV = 2500 VB = 0.8 T

r = cm

6.Hard

A long air-core solenoid has 500 turns, a length of 40 cm and a diameter of 1.5 cm. Find the energy W stored in its magnetic field when it carries 2.5 A.

N = 500l = 40 cm⌀ = 1.5 cmI = 2.5 Aμ₀ = 4π × 10⁻⁷ T·m/A

W = µJ

Answer key

1. B = 120 µT
2. r = 2.5 cm
3. ε = 960 mV
4. T = 130.3 ns
5. r = 0.9033 cm
6. W = 433.7 µJ

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