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

Law of Faraday:

- V
_{ind }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

**Example**

See the figure above.

The area of the turn is 40 cm^{2}

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 90^{o} . In that situation the magnetic flux is maximal

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

V_{ind }=- N ( ΔΦ/Δt)

ΔΦ = Φ_{max }– 0 = B A = 0.020 (40 x 10^{-4})= 8.0 x 10^{-5} Wb

V_{ind }= 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

U_{ind}_{ }= I_{ind}_{ }R

1.6 x 10^{-2 }= I_{ind }0.20

I_{ind} = 8.0 x 10^{-2 }A