A. Constant magnetic flux
B. Increasing magnetic flux
C. Alternating magnetic flux
D. Alternating electric flux
Answer: C. Alternating magnetic flux
Explanation:
A basic transformer contains two magnetically coupled coils on a common core.
If an alternating voltage is given to one winding (primary), due to electromagnetic and mutual induction there is a voltage induced in the secondary winding where the load can be connected.
The energy transfer from one winding to another is entirely through the magnetic medium and known as transformer action based on the principle of electromagnetic induction proposed by Faraday.
Therefore, transformer action requires an alternating or time-varying magnetic flux to transfer power from the primary side to the secondary side since induced emf in the winding is due to flux linkage.