CBSE Class 12 · 2005 · Alternating CurrentShort Answer

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Explain, with the help of a diagram, the principle and working of an a.c. generator. Write the expression for the e.m.f. generated in the coil in terms of its speed of rotation.

Answer: Principle: electromagnetic induction; $e = N B A ω sin ω t$ with peak value $e_{0} = N B A ω \propto ω$ .

Solution

Principle: An a.c. generator works on electromagnetic induction. When a coil is rotated in a uniform magnetic field, the magnetic flux through it changes continuously and an alternating emf is induced.
Working: A rectangular coil of

N

turns and area

A

is rotated with angular speed

ω

in a field

B

. When the coil normal makes angle

ω t

with

B

, the flux linked is

ϕ = N B A cos ω t

so the induced emf is

e = - \frac{d ϕ}{d t} = N B A ω sin ω t = e_{0} sin ω t

Slip rings and brushes feed this alternating emf to the external circuit. Its peak value

e_{0} = N B A ω

is proportional to the speed of rotation

ω

e = N B A ω sin ω t

CBSE Class 12 Board · 2005 · Subjective

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CBSE Class 12 · 2005 · Alternating CurrentShort Answer

Solution

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