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 = 20 APr = ?B = 133.3 µT

A long straight wire carries 20 A. At what distance r from the wire is the magnetic flux density 133.3 µT?

I = 20 AB = 133.3 µTμ₀ = 4π × 10⁻⁷ T·m/A
r = cm
2.Easy
I = 5 AR = 5 cmB = ?N = 20

A flat circular coil of 20 turns and radius 5 cm carries a current of 5 A. Find the magnetic flux density B at its centre.

N = 20I = 5 AR = 5 cmμ₀ = 4π × 10⁻⁷ T·m/A
B = mT
3.Medium
R = 0.5 Ωv = 4 m/sL = 25 cmB = 0.4 T

A metal rod 25 cm long slides at 4 m/s along two rails in a uniform field of 0.4 T into the page. The rails are joined by a resistor of 0.5 Ω; the rod and rails have negligible resistance. Find the force F needed to keep the rod moving at constant speed (no friction).

B = 0.4 TL = 25 cmv = 4 m/sR = 0.5 Ω
F = mN
4.Medium
−vBF = ?

An electron 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
E = 2 × 10⁵ V/m, B1​ = 0.25 T

In a velocity selector, crossed fields E = 2 × 10⁵ V/m and B = 0.25 T let only ions of one speed pass straight through. Find that speed v.

E = 2 × 10⁵ V/mB1 = 0.25 T
v = m/s
6.Hard
Bn = 1200 rpm20 cm × 10 cmN = 250B = 0.05 T

A coil of 250 turns, 20 cm × 10 cm, rotates at 1200 rpm in a uniform field of 0.05 T about an axis perpendicular to the field. Find the peak emf E0.

N = 250A = 20 cm × 10 cmB = 0.05 Tn = 1200 rpm
E0 = V

Answer key

  1. 1. r = 3.001 cm
  2. 2. B = 1.257 mT
  3. 3. F = 80 mN
  4. 4. to the left
  5. 5. v = 800000 m/s
  6. 6. E0 = 31.42 V

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