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 solenoid 10 cm long carries 2.5 A. How many turns N must it have for a flux density of 47.12 mT inside?

I = 2.5 AL = 10 cmB = 47.12 mTμ₀ = 4π × 10⁻⁷ T·m/A

N =

2.Easy

A flat circular coil of 50 turns and radius 6 cm carries a current of 3 A. Find the magnetic flux density B at its centre.

N = 50I = 3 AR = 6 cmμ₀ = 4π × 10⁻⁷ T·m/A

B = mT

3.Medium

An electron moves down the page through a uniform magnetic field pointing into the page. Click the direction of the magnetic force on it.

v: down the pageB: into the page

1up the page
2to the right
3down the page
4to the left

4.Medium

An alpha particle moves on a circle in a uniform magnetic field of 0.25 T. Find the time T it takes for one revolution.

m = 6.645 × 10⁻²⁷ kg|q| = 3.204 × 10⁻¹⁹ CB = 0.25 T

T = ns

5.Hard

A coil of 20 turns, 12 cm × 20 cm, rotates at 1800 rpm in a uniform field of 0.05 T about an axis perpendicular to the field. Find the peak emf E₀.

N = 20A = 12 cm × 20 cmB = 0.05 Tn = 1800 rpm

E₀ = V

6.Hard

A coil of 250 turns, 5 cm × 15 cm, rotates in a uniform field of 0.4 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 66.64 V?

N = 250A = 5 cm × 15 cmB = 0.4 TE_rms = 66.64 V

n = rpm

Answer key

1. N = 1500
2. B = 1.571 mT
3. to the left
4. T = 521.2 ns
5. E₀ = 4.524 V
6. n = 1200 rpm

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