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.

New worksheet Practise online with hints

For teachers: free to print, copy and use in class. Every new worksheet has new values and its own answer key. A link to ExamProblems on your course page is appreciated.

Name: ____________________ Date: ____________

1.Easy

A flat circular coil of 10 turns and radius 12 cm carries a current of 3 A. Find the magnetic flux density B at its centre.

N = 10I = 3 AR = 12 cmμ₀ = 4π × 10⁻⁷ T·m/A

B = µT

2.Easy

A solenoid 20 cm long has 1000 turns and carries 2 A. Find the magnetic flux density B inside it, far from the ends.

N = 1000L = 20 cmI = 2 Aμ₀ = 4π × 10⁻⁷ T·m/A

B = mT

3.Medium

A metal rod 50 cm long slides at 4 m/s along two rails in a uniform field of 0.5 T into the page. The rails are joined by a resistor of 2.5 Ω; the rod and rails have negligible resistance. Find the force F needed to keep the rod moving at constant speed (no friction).

B = 0.5 TL = 50 cmv = 4 m/sR = 2.5 Ω

F = mN

4.Medium

Two long parallel wires 2 cm apart carry currents of 2 A and 30 A in the same direction. Find the force per metre of length F/L between them.

I₁ = 2 AI₂ = 30 Ad = 2 cmμ₀ = 4π × 10⁻⁷ T·m/A

F/L = µN/m

5.Hard

In a velocity selector, crossed fields E = 1 × 10⁴ V/m and B = 0.4 T let only ions of one speed pass straight through. Find that speed v.

E = 1 × 10⁴ V/mB₁ = 0.4 T

v = m/s

6.Hard

A coil of 100 turns, 12 cm × 10 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 39.99 V?

N = 100A = 12 cm × 10 cmB = 0.25 TE_rms = 39.99 V

n = rpm

Answer key

1. B = 157.1 µT
2. B = 12.57 mT
3. F = 100 mN
4. F/L = 600 µN/m
5. v = 25000 m/s
6. n = 1800 rpm

Full step-by-step solutions: practise this topic on examproblems.com.