Question

If the number of poles of an alternator is increased, the generated e.m.f.

• A. increases
• B. decreases
• C. remain the same
• D. none of the above

Hint:

In alternators, the number of poles affects synchronous speed but not the magnitude of generated emf when frequency and flux are constant.

Answer 1

The Correct Option is C

Step 1: Recall the emf equation of an alternator.
The generated emf of an alternator is given by
\[ E = 4.44 k_w f \Phi T \]
Step 2: Analyze the effect of number of poles.
The frequency of generated emf is related to speed and number of poles by
\[ f = \frac{P N}{120} \]
If the number of poles increases, the synchronous speed decreases proportionally for constant frequency operation.
Step 3: Conclusion.
Since frequency and flux per pole remain constant under rated conditions, the generated emf does not change with increase in number of poles.
% Final Answer \[ \boxed{\text{The generated emf remains the same}} \]