Change of magnetic flux and electromagnetic induction                           

A change in the magnetic flux in a closed circuit (coil) induces  a potential difference.

Law of Faraday:

  • Vind  average induced potential difference in V
  • N      amount of loops of the coil
  • ΔΦ   change of magnetic flux in Wb
  • Δ t    time interval in which change occurs in s



See the figure above.

The area of the turn is  40 cm2

The magnitude of the magnetic induction is 0.020 T

The turn is rotated.

At the moment of the figure the field lines are parallel to  the turn.

So the magnetic flux is 0 Wb

After  0.0050 s the turn has rotated  90o . In that  situation the magnetic flux is maximal

Determine the average induced potential difference (emf) in this time interval.

Vind =- N ( ΔΦ/Δt)

 ΔΦ = Φmax – 0 = B A = 0.020 (40 x 10-4)= 8.0 x 10-5 Wb

Vind = 1 (8.0 x 10-5)/0.0050 = 1.6 x 10-2 V

An induction current is produced when A is connected to B

The resistance of the circuit is 0.20 Ω


Uind = Iind R

1.6 x 10-2 = Iind  0.20

Iind = 8.0 x 10-2 A

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