Question

(a) Draw a labelled diagram of an electric generator. Explain its construction and working in brief.
(b) Write down any two characteristics of magnetic field lines of a bar magnet.

Answer 1

(a)Principle:It works on the principle of Faraday's law of EM induction.Whenever a coil is rotated in a uniform magnetic field about an axis perpendicular to the field a magnetic flux linked with coil changes and an induced emf is set up across its ends.The coil is horizontal and is rotated clockwise.

$\varphi =NBA\cos \omega t$

Induced emf $\epsilon =\frac{d\varphi }{dt}$

=$-\frac{d\left(NBA\cos \omega t\right)}{dt}$

=$NBA\omega \sin \omega t$

Let ${\epsilon }_0$ be peak value of induced emf

$\epsilon$ =${\epsilon }_0\sin \omega t$ where ${\epsilon }_0=NBA\omega$

(b) Characterstics:

(i)The field lines attempt to form closed loops from pole to pole.

(ii)The field lines never cross each other.