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
B0.25 T4 A90°L = 15 cm

A straight wire 15 cm long carries 4 A at an angle of 90° to a uniform magnetic field of 0.25 T. Find the magnitude of the force F on the wire.

B = 0.25 TI = 4 AL = 15 cmθ = 90°
F = N
2.Easy
I = 3 AR = 12 cmB = ?

A single circular loop of wire with radius 12 cm carries a current of 3 A. Find the magnetic flux density B at its centre.

N = 1I = 3 AR = 12 cmμ₀ = 4π × 10⁻⁷ T·m/A
B = µT
3.Medium
nBA = 80 cm², N = 250B: 0.1 → 0.7 T

A coil of 250 turns has an area of 80 cm². A uniform field perpendicular to the coil rises steadily from 0.1 T to 0.7 T in 20 ms. Find the average induced emf ε.

N = 250A = 80 cm²B: 0.1 T → 0.7 TΔt = 20 ms
ε = V
4.Medium
+vBF = ?

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

v: 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 = ?20 cm × 5 cmN = 200B = 0.25 T

A coil of 200 turns, 20 cm × 5 cm, rotates in a uniform field of 0.25 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 66.64 V?

N = 200A = 20 cm × 5 cmB = 0.25 TErms = 66.64 V
n = rpm
6.Hard
I = 2.5 Al = 15 cmN = 300, ⌀ 2.5 cm

A long air-core solenoid has 300 turns, a length of 15 cm and a diameter of 2.5 cm. Find the energy W stored in its magnetic field when it carries 2.5 A.

N = 300l = 15 cm⌀ = 2.5 cmI = 2.5 Aμ₀ = 4π × 10⁻⁷ T·m/A
W = mJ

Answer key

  1. 1. F = 0.15 N
  2. 2. B = 15.71 µT
  3. 3. ε = 60 V
  4. 4. to the right
  5. 5. n = 1800 rpm
  6. 6. W = 1.157 mJ

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