At a certain instant in AC generator, when the normal of the plane (rectangular coil) makes an angle of 270 degrees with with the magnetic induction B, the value of emf is:

$E = -NAB\omega$

My teachers would usually say that this is the minimum value of emf that a generator produces. Does it really mean that? Or does the negative sign only mean that emf is at its peak value but the current is flowing in opposite direction?


Yes. That's why it's named as alternating current. Briefing...

The magnetic flux linked to the coil is $\phi=NBA\ cos(\omega t)$ and the emf induced (according to Lenz' correction of Faraday's law, $$e=-NBA\frac{d(cos(\omega t))}{dt}=NBA\omega\ sin(\omega t)$$

Here, $NBA\omega$ is a constant which can be replaced by $E_0$ which is the maximum value of emf induced along the coil. When $\omega t=3\pi/2$ (i.e) when the normal makes the 270-degree angle, $e=-E_0$ which is the maximum negative voltage (or) simply the flow of current in the opposite direction. Please have an overview on the Wiki article...


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.