Final answer:
The question pertains to the induction of average emf when a current changes, which is calculated using Faraday's law of induction. However, the lack of information on coil characteristics and magnetic flux changes in the question makes it impossible to calculate the emf directly.
Step-by-step explanation:
The question is about calculating the average electromotive force (emf) in a scenario where a current is turned on rapidly. To determine the average emf that is induced in a situation like this, one must understand the concept of mutual inductance or self-inductance. From the example provided, the induced emf is essentially the change in magnetic flux over the change in time, given by Faraday's law of induction. However, the question does not provide enough information to calculate the emf directly, as the inductance of the coil and the exact nature of the change in current (i.e., the initial magnetic flux and the final magnetic flux) is not specified. Without additional details such as the number of turns on the coil, the area of the coil, and the magnetic field strength, the emf cannot be computed.