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 long straight wire carries a current of 20 A. Find the magnetic flux density B at point P, 4 cm from the wire.

I = 20 Ar = 4 cmμ₀ = 4π × 10⁻⁷ T·m/A

B = µT

2.Easy

A solenoid 20 cm long has 500 turns. Which current I gives a magnetic flux density of 15.71 mT inside it?

N = 500L = 20 cmB = 15.71 mTμ₀ = 4π × 10⁻⁷ T·m/A

I = A

3.Medium

A coil of 25 turns has an area of 50 cm². The coil sits in a uniform field of 0.3 T perpendicular to its plane, and the field is switched off in 250 ms. Find the average induced emf ε.

N = 25A = 50 cm²B = 0.3 TΔt = 250 ms

ε = mV

4.Medium

A metal rod 30 cm long slides at 4 m/s along two rails in a uniform field of 0.6 T into the page. The rails are joined by a resistor of 4 Ω; the rod and rails have negligible resistance. Find the current I.

B = 0.6 TL = 30 cmv = 4 m/sR = 4 Ω

I = mA

5.Hard

In a velocity selector, crossed fields E = 2 × 10⁴ V/m and B = 0.05 T let only ions of one speed pass straight through. Find that speed v.

E = 2 × 10⁴ V/mB₁ = 0.05 T

v = m/s

6.Hard

A coil of 100 turns, 5 cm × 15 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 = 100A = 5 cm × 15 cmB = 0.05 Tn = 1200 rpm

E₀ = V

Answer key

1. B = 100 µT
2. I = 5.001 A
3. ε = 150 mV
4. I = 180 mA
5. v = 400000 m/s
6. E₀ = 4.712 V

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