The a.c generator consists of:
- an armature- a rectangular coil consisting of a large number of an insulated wire wound on a laminated soft iron core
- a magnetic field- created by the curved poles of a horse shoe magnet or an electromagnetÂ
- two copper slip rings R1, R2– to which ends of rectangular coils are connected and which rotate with the armature
- two stationary carbon brushes : which are made to press lightly against the slip rings Â
An alternating voltage whose waveform is obtained above at the terminals by means of carbon brushes and slip rings
If the coil of area A rotates in magnetic field of strength B. Let the normal to the coil make an angle θ with the field as shown,
Flux θ through the coil is given by φ = ABCosθ ________(1)
If there are N number of turns in the coil, then, φ = NABcosθ _________(2)
If the coil turns with a steady angular velocity ω is given by
ω = \( \frac{dθ}{dt} \) _________(3)
the induced e.m.f is given byÂ
E = \( \frac{- dθ}{dt} \) _________(4)
The above equation follows from Faraday’s and Lenz’s laws
E = \( \frac{- dθ}{dt} = \frac{- d}{dt} \scriptsize (NABcosθ) \)Â
E = \( \scriptsize – NAB  \normalsize \frac{ d}{dt} \scriptsize (cosθ) \)
E = \( \scriptsize NAB sinθ  \normalsize \frac{ dθ}{dt} \) _______(5) Â
From equation (3)  ω = \( \frac{dθ}{dt} \)Â
∴ E = NABω sinθ __________(6), if θ = 90 , then equation 6 becomes
 E = NABω = EO ___________(7)
where EO is the maximum induced e.m.f which occurs when the coil is parallel to the field direction.
E = EOsinθ, but ω = \( \frac{dθ}{dt} \), θ = ωt
 E = EOsinω t ______________(8)
Alternating current a.c is a current which changes continually in direction while passing through a conductor
Measurement of A.C
An a.c can be measured by:
Hot-wire ammeter- using the heating effect of current
Moving iron ammeter- using the magnetic field of current
Moving coil galvanometer to which a rectifier is attached to convert a.c to d.c
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