Correct option is D
· In a single-phase transformer, the primary and secondary windings are stationary relative to each other.
· The induced voltage in the secondary winding is due to the changing magnetic flux produced by the alternating current in the primary winding.
· Since there is no relative motion between the coils, the frequency of the induced voltage in the secondary winding remains the same as the frequency of the alternating current in the primary winding. Thus, the frequency of the induced voltage is constant.
