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 straight wire 100 cm long lies at 60° to a uniform magnetic field of 0.8 T. The magnetic force on it is 2.078 N. Find the current I.

B = 0.8 TF = 2.078 NL = 100 cmθ = 60°

I = A

2.Easy

A long straight wire carries a current of 40 A. Find the magnetic flux density B at point P, 8 cm from the wire.

I = 40 Ar = 8 cmμ₀ = 4π × 10⁻⁷ T·m/A

B = µT

3.Medium

A metal rod 25 cm long slides at 10 m/s along two rails in a uniform field of 1 T into the page. The rails are joined by a resistor of 10 Ω; the rod and rails have negligible resistance. Find the force F needed to keep the rod moving at constant speed (no friction).

B = 1 TL = 25 cmv = 10 m/sR = 10 Ω

F = mN

4.Medium

A metal rod 50 cm long slides at 3 m/s along two rails in a uniform field of 0.6 T into the page. Find the induced emf ε between its ends.

B = 0.6 TL = 50 cmv = 3 m/s

ε = mV

5.Hard

A proton starts from rest, is accelerated through a potential difference of 1000 V and then enters a uniform magnetic field of 0.25 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 = 0.25 T

r = cm

6.Hard

In a velocity selector, crossed fields E = 8 × 10⁴ V/m and B = 0.1 T let only ions of one speed pass straight through. Find that speed v.

E = 8 × 10⁴ V/mB₁ = 0.1 T

v = m/s

Answer key

1. I = 2.999 A
2. B = 100 µT
3. F = 62.5 mN
4. ε = 900 mV
5. r = 1.828 cm
6. v = 800000 m/s

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