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Describe the construction and working of an AC generator and arrive at the expression for the emf induced in it. |
Answer» Solution :Construction : AC generator consists of a rectangular coil abcd of insulated copper WIRE wound on a soft iron core. The coil (armature) is rotated in a strong uniform magnetic field. There axis of rotation is perpendicular to the direction of magnetic field. The two ENDS of rectangular coil are connected to slip rings `R_1` and `R_2` which are insulated each other. The two carbon stationary brushes` B_1 and B_2` make contact with `R_1` and `R_2` WORKING  In the above figure N and S are poles of a MAGNET, `theta ` is the angle between the directions of magnetic field B and area vector A. When the coil is rotated in the magnetic field, the flux linked with the coil varies: At" , any instant of time .t., A cos `theta ` is the component of area vector along the direction B: The magnetic flux linked with the coil at any instant of time .t. is given by `phi_n =B xx`component of area vector along the field direction. For I turn `phi_B .=BA cos theta ` For n turns `phi_B =nAB cos theta ` `phi _B n ABcosomega t -------(1)[ :.theta = omega t]` where `. omega `. is the angular velocity of the coil at time t. From the Faraday.s second LAW, `e=- ( d phi)/(dt) ` ` =- (d)/(dt) [ nABcosomegat] [from(1) phi=nAB cosomega ]` `e=- (-nAB)[- sinomega t]xx omega ` ` e= nABomegat ` ` e=e_0sin( omegat)` where `e_0` is the peak value of `emf = nAB omega ` |
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