# The output frequency of an alternator depends on -

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The output frequency of an alternator depends on -

1. Type of winding
2. Number of poles and rotational speed
3. Number of poles only
4. Rotational speed only

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Correct Answer - Option 2 : Number of poles and rotational speed

The rotor speed of the alternator is given by

$N = {{120f} \over P}$       ........(1)

Where,

N = Speed of rotor in rpm

f = Frequency of generated emf

P = Number of Poles

From equation (1)

$f = {{NP} \over 120}$

$f \propto {NP}$

So the output frequency of an alternator depends on both the number of poles and rotational speed.