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
I = 2 AR = 8 cmB = ?N = 25

A flat circular coil of 25 turns and radius 8 cm carries a current of 2 A. Find the magnetic flux density B at its centre.

N = 25I = 2 AR = 8 cmμ₀ = 4π × 10⁻⁷ T·m/A
B = µT
2.Easy
I = 2.5 AR = 15 cmB = ?N = 25

A flat circular coil of 25 turns and radius 15 cm carries a current of 2.5 A. Find the magnetic flux density B at its centre.

N = 25I = 2.5 AR = 15 cmμ₀ = 4π × 10⁻⁷ T·m/A
B = µT
3.Medium
R = 5 Ωv = 2.5 m/sL = 30 cmB = 0.1 T

A metal rod 30 cm long slides at 2.5 m/s along two rails in a uniform field of 0.1 T into the page. The rails are joined by a resistor of 5 Ω; the rod and rails have negligible resistance. Find the force F needed to keep the rod moving at constant speed (no friction).

B = 0.1 TL = 30 cmv = 2.5 m/sR = 5 Ω
F = mN
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
V = 1000 VB = 0.5 Tr = ?

A proton starts from rest, is accelerated through a potential difference of 1000 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 = 1.673 × 10⁻²⁷ kg|q| = 1.602 × 10⁻¹⁹ CV = 1000 VB = 0.5 T
r = cm
6.Hard
Bn = ?5 cm × 25 cmN = 20B = 0.5 T

A coil of 20 turns, 5 cm × 25 cm, rotates in a uniform field of 0.5 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 33.32 V?

N = 20A = 5 cm × 25 cmB = 0.5 TErms = 33.32 V
n = rpm

Answer key

  1. 1. B = 392.7 µT
  2. 2. B = 261.8 µT
  3. 3. F = 0.45 mN
  4. 4. clockwise
  5. 5. r = 0.914 cm
  6. 6. n = 3600 rpm

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