AdvancedA-001-001-005
What is meant by "back EMF"?
A
Answer
Advanced theory and components
Type
A
A voltage that opposes the applied EMF
B
A current that opposes the applied EMF
C
A current equal to the applied EMF
D
An opposing EMF equal to R times C percent of the applied EMF
Answer Notes
EMF stands for Electromotive Force, which is a formal scientific term for voltage. According to Lenz's Law, when a changing current passes through an inductor, it creates a fluctuating magnetic field that induces a voltage across that same coil.
This induced voltage always acts in a polarity that opposes the original change in current that created it. Because it pushes back against the applied supply voltage (the source EMF), it is commonly referred to as 'back EMF' or 'counter EMF.'
Distractors suggesting it is a 'current' rather than a voltage are fundamentally incorrect because EMF specifically defines a force measured in volts. Options mentioning RC combinations are completely unrelated to the definition of back EMF, which is an inductive phenomenon.
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After two time constants, the capacitor in an RC circuit is charged to what percentage of the supply voltage?