Correct Answer:
C. Back EMF
In the context of an electric motor, such as those used in electric cars, the term "Back EMF" (Electromotive Force) is precisely what is called the voltage generated across the motor's windings. This voltage is induced due to the rotation of the motor's armature within a magnetic field. According to Lenz's Law, this induced voltage opposes the applied voltage that drives the motor. As the motor spins faster, the back EMF increases, effectively limiting the current flowing through the motor and playing a crucial role in regulating its speed and power output. It is a fundamental principle of motor operation, directly impacting efficiency and performance.
- Resistance: Resistance is a property of a material that opposes the flow of electric current, converting electrical energy into heat. While motor windings have resistance, back EMF is an induced voltage that actively opposes the applied voltage, not merely a static resistive property.
- Inductance: Inductance is the property of an electrical conductor to oppose a change in the electric current flowing through it by generating an electromotive force (EMF) proportional to the rate of change of the current. While electric motors are highly inductive, back EMF specifically refers to the voltage induced by the physical motion of the coil in a magnetic field, not just by changes in current.
- None: Since "Back EMF" is the correct and specific scientific term for this phenomenon in an electric motor, this option is incorrect.