Final answer:
As the emf in the primary coil of a transformer is increased, the magnetic field strength and the rate of change in magnetic flux through the secondary coil also increase, thereby increasing the induced emf and current in the secondary coil.
Step-by-step explanation:
The process taking place is based on Faraday's law of induction, which states that a change in magnetic flux through a coil induces an electromotive force (emf) in that coil. As the emf in the primary coil is increased, assuming the frequency of the alternating current remains constant, this effectively increases the magnetic field strength, and thus the change in magnetic flux through the secondary coil also increases. Consequently, the induced emf and current in the secondary coil will increase proportionally.
Since transformers operate on alternating current, the input voltage is periodically reversed. This action results in a change in direction of the magnetic field and a corresponding change in magnetic flux through the secondary coil, thereby inducing an alternating emf (and hence current) in the secondary coil.
Factors such as the number of turns in the coils and the presence of an iron core, which increases the magnetic field strength (as it has a higher magnetic permeability than air), also play significant roles in determining the magnitude of the induced emf and current. Moreover, according to Faraday's law, the induced emf is proportional to the rate of change of magnetic flux, so an increase in the rate of change will lead to a higher induced emf.