What does "back EMF" refer to in electric motors?

Back EMF, or back electromotive force, refers to the voltage generated by the motor as it rotates. When a motor is powered and begins to turn, it not only draws current from the power supply but also generates its own voltage due to its rotation in the magnetic field. This generated voltage opposes the applied voltage, which is why it is termed "back" EMF.

As the speed of the motor increases, the back EMF also increases, which reduces the net voltage across the motor's windings and, consequently, the current flowing through them. This mechanism allows the motor to self-regulate its speed and current draw. Understanding back EMF is crucial for designing motor control systems, as it influences performance characteristics like efficiency and torque.

The resistance faced by the motor, the speed at which the motor operates, and the initial current drawn at startup are different aspects that do not accurately capture the concept of back EMF, which specifically focuses on the voltage produced by the motor during operation.