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
B = ?I = 1 AL = 20 cmN = 500

A solenoid 20 cm long has 500 turns and carries 1 A. Find the magnetic flux density B inside it, far from the ends.

N = 500L = 20 cmI = 1 Aμ₀ = 4π × 10⁻⁷ T·m/A
B = mT
2.Easy
I = 5 AR = 15 cmB = ?N = 25

A flat circular coil of 25 turns and radius 15 cm carries a current of 5 A. Find the magnetic flux density B at its centre.

N = 25I = 5 AR = 15 cmμ₀ = 4π × 10⁻⁷ T·m/A
B = µT
3.Medium
−v = 5 × 10⁶ m/sB = 10 mT

An electron moves on a circle in a uniform magnetic field of 10 mT. Find the time T it takes for one revolution.

m = 9.109 × 10⁻³¹ kg|q| = 1.602 × 10⁻¹⁹ CB = 10 mT
T = ns
4.Medium
R = 2.5 Ωv = 4 m/sL = 80 cmB = 0.1 T

A metal rod 80 cm long slides at 4 m/s along two rails in a uniform field of 0.1 T into the page. The rails are joined by a resistor of 2.5 Ω; the rod and rails have negligible resistance. Find the power P dissipated in the resistor.

B = 0.1 TL = 80 cmv = 4 m/sR = 2.5 Ω
P = mW
5.Hard
I = 3 Al = 15 cmN = 1500, ⌀ 1.5 cm

A long air-core solenoid has 1500 turns, a length of 15 cm and a diameter of 1.5 cm. Find the energy W stored in its magnetic field when it carries 3 A.

N = 1500l = 15 cm⌀ = 1.5 cmI = 3 Aμ₀ = 4π × 10⁻⁷ T·m/A
W = mJ
6.Hard
I = 4 Al = 25 cmN = 200, ⌀ 1.5 cm

A long air-core solenoid has 200 turns, a length of 25 cm and a diameter of 1.5 cm. Find the energy W stored in its magnetic field when it carries 4 A.

N = 200l = 25 cm⌀ = 1.5 cmI = 4 Aμ₀ = 4π × 10⁻⁷ T·m/A
W = µJ

Answer key

  1. 1. B = 3.142 mT
  2. 2. B = 523.6 µT
  3. 3. T = 3.573 ns
  4. 4. P = 40.96 mW
  5. 5. W = 14.99 mJ
  6. 6. W = 284.2 µJ

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