Subelement A: Principles— Topic 2: Magnetism
Question 3-2A5
Element 3 (GROL)What is meant by the term “back EMF”?
Explanation
Back EMF, or back electromotive force, is a voltage generated within an inductive component, such as an inductor or the windings of a motor, whenever the current flowing through it changes. According to Lenz's Law, this induced voltage always acts in a direction that opposes the change in current that caused it. Consequently, it directly opposes the applied voltage (EMF) driving that current change. This is a fundamental concept in AC circuit theory and motor operation.
Therefore, option C is correct: back EMF is a voltage that opposes the applied EMF. Options A and D are incorrect because back EMF is a *voltage* (an electromotive force), not a current. Option B incorrectly ties back EMF to an RC time constant, which is relevant to resistor-capacitor circuits, not the inductive effect of back EMF.
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