What type of input is applied to the rotor in a control transformer?

The input applied to the rotor in a control transformer is best understood in the context of how transformers operate. In a transformer, including a control transformer, the primary function revolves around electromagnetic induction. The rotor is typically involved in the transformation of electrical energy, but it is not where the electrical input is directly applied.

Instead, the rotor interacts predominantly with the magnetic field generated in the transformer. The magnetic input is a result of the alternating current flowing through the primary winding, creating a varying magnetic field that induces voltage in the secondary winding. Hence, the energy transfer due to the changing magnetic field is crucial for the functioning of the control transformer.

Therefore, the correct answer highlights the magnetic nature of the input involved in the operation of the rotor within the context of a control transformer, emphasizing the importance of magnetic fields in the transformation process.