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
B0.4 TI = ?90°L = 15 cm

A straight wire 15 cm long lies at 90° to a uniform magnetic field of 0.4 T. The magnetic force on it is 0.18 N. Find the current I.

B = 0.4 TF = 0.18 NL = 15 cmθ = 90°
I = A
2.Easy
I = 0.5 AR = 15 cmB = ?N = 20

A flat circular coil of 20 turns and radius 15 cm carries a current of 0.5 A. Find the magnetic flux density B at its centre.

N = 20I = 0.5 AR = 15 cmμ₀ = 4π × 10⁻⁷ T·m/A
B = µT
3.Medium
nBA = 50 cm², N = 20B = 0.4 T

A coil of 20 turns has an area of 50 cm². The coil sits in a uniform field of 0.4 T perpendicular to its plane, and the field is switched off in 20 ms. Find the average induced emf ε.

N = 20A = 50 cm²B = 0.4 TΔt = 20 ms
ε = V
4.Medium
dB/dt < 0I = ?

A circular loop lies in a uniform magnetic field pointing into the page. The field strength is decreasing. Click the direction of the induced current in the loop as seen in the drawing.

B: into the pagedB/dt < 0
  1. 1clockwise
  2. 2counterclockwise
5.Hard
L1​ = 10 mH200 A/sL2​ = 100 mHk = 0.5ε = ?

Two coils with self-inductances of 10 mH and 100 mH have a coupling coefficient of 0.5. The current in the first coil changes at 200 A/s. Find the emf ε induced in the second coil.

L1 = 10 mHL2 = 100 mHk = 0.5di/dt = 200 A/s
ε = V
6.Hard
V = 2500 VB = 0.5 Tr = ?

An alpha particle starts from rest, is accelerated through a potential difference of 2500 V and then enters a uniform magnetic field of 0.5 T at right angles. Find the radius r of its path in the field.

m = 6.645 × 10⁻²⁷ kg|q| = 3.204 × 10⁻¹⁹ CV = 2500 VB = 0.5 T
r = cm

Answer key

  1. 1. I = 3 A
  2. 2. B = 41.89 µT
  3. 3. ε = 2 V
  4. 4. clockwise
  5. 5. ε = 3.162 V
  6. 6. r = 2.037 cm

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