A 3-phase 440 V, 50 Hz induction motor has 4% slip. The frequency of rotor e.m.f. will be

Answer: Option C

The slip in an induction motor is the difference between the synchronous speed and the actual rotor speed, expressed as a percentage of the synchronous speed. The frequency of the rotor emf is related to the slip and the supply frequency. For a 3-phase induction motor:

Supply Frequency (f_s): 50 Hz
Slip (s): 4% or 0.04
The frequency of the rotor emf (f_r) can be calculated using the formula:

f_r = s × f_s

Substituting the values:

f_r = 0.04 × 50 Hz = 2 Hz

Therefore, the frequency of the rotor emf is 2 Hz.