Correct Answer - Option 1 : 60 Hz
Concept:
An alternator rotates with synchronous speed. The synchronous speed is given by
\({N_s} = \frac{{120f}}{P}\)
where f is the supply frequency
P is the number of poles
The frequency of induced emf in an alternator is the same as the supply frequency.
So, the frequency of induced emf is
\(f = \frac{{PN}}{{120}}\)
Calculation:
Given that, number of poles (P) = 6
Synchronous speed (Ns) = 1200 rpm
Frequency \(f = \frac{{6 \times 1200}}{{120}} = 60\;Hz\)