# Laws of Electromagnetic Induction

Faraday’s laws of electromagnetic induction-Magnitude of induced e.m.f.

• Whenever the magnetic flux linked with a closed circuit changes, an e.m.f. is induced in the circuit. The induced e.m.f. lasts so long as the change in flux lasts.
• The magnitude of the induced e.m.f. is directly proportional to rate of change of flux linkage or rate of flux cutting. $$E\propto \frac{d\varnothing }{dt}$$ or $$E~=~a~constant*~\frac{d\varnothing }{dt}~$$

The constant is taken to be one.

$$E=\frac{d\varnothing }{dt}$$

This constant is taken to be one. To make the constant one we define one weber as the magnitude flux which induces in one turn coil an e.m.f. of one volt, when flux is reduced to zero in one second.

Let the change in flux be d  in a time dt. If there are N turns in the coil then the induced e.m.f. here N∅ is called the magnetic flux linkage. SI unit of Nφ, is weber – turn.

$$Induced~current~in~the~circuit=~\frac{Induced~emf}{Resistancein~the~circuit}$$ $$I=\frac{d\varnothing }{Rdt}$$

To show the sense of induced e.m.f. a negative sign is put. $$E=-\frac{d\varnothing }{dt}$$  and $$I=-\frac{d\varnothing }{Rdt}$$ the negative sign is put in accordance with Lenz’s law.