The alternator and the sinusoidal EMF

By mechanically rotating a loop in a uniform magnetic field one obtains an EMF that varies sinusoidally in time:

$\ev{\text{FEM}(t) = \text{FEM}_0\,\sin(\omega t)}$

As the loop rotates, the angle between its normal and the field changes continuously: the flux $\Phi_B = B\,A\cos(\omega t)$ oscillates, and its derivative — the induced EMF — is a sine wave. This is the principle behind every alternator, from small bicycle dynamos to the giant turbines of hydroelectric power stations.

Faraday, the genius without a degree

Michael Faraday (1791–1867), the son of a London blacksmith, never attended university. He was working as an errand boy for a bookbinder when, reading the books that passed through his hands, he fell in love with chemistry and physics. He managed to become an assistant to Humphry Davy at the Royal Institution, where in 1831 he discovered electromagnetic induction using a strikingly simple apparatus: two coils wound around an iron ring. When asked what use this discovery might have, he is said to have replied: “I do not know, but I am sure that one day you will be able to tax it.” Today the entire world’s electricity grid is based on his principles.

Collegamenti

Argomenti: Electromagnetic induction Concetti: Alternating current · Faraday-Neumann-Lenz law

Esercizi collegati: Ideal transformer · Alternator: from the peak EMF to the angular frequency · Bicycle dynamo