NEIEP Mechanics Practice Exam

At what point is CEMF greatest in an inductive circuit?

1. At zero current

2. When the circuit is complete

3. When the rate of change for current is maximum

4. When capacitance is highest

The correct answer is: When the rate of change for current is maximum

In an inductive circuit, CEMF, or counter electromotive force, reaches its greatest value when the rate of change of current is maximum. This phenomenon is rooted in Faraday's law of electromagnetic induction, which states that the induced electromotive force in a circuit is directly proportional to the rate of change of magnetic flux through the circuit. In the context of an inductive circuit, when the current changes rapidly, the magnetic field around the inductor also changes quickly. This rapid change induces a higher CEMF in the opposite direction of the applied voltage, as the inductor resists the change in current due to its stored energy in the magnetic field. Thus, when the rate of change of the current is at its peak, the induced CEMF will also be at its peak, effectively opposing the source current. The other choices do not accurately reflect when the CEMF would be greatest. CEMF is not maximized at zero current, as there would be no change in current, and therefore no induced voltage. While the circuit being complete is necessary for current flow, it does not by itself dictate the level of CEMF. Finally, the capacitance level does not influence CEMF in an inductive circuit