How does a back voltage develop in a direct-current motor as its speed increases?

In a direct-current (DC) motor, the development of back voltage—also known as counter electromotive force—is a direct result of the principles of electromagnetic induction as the rotor spins within a magnetic field.12

As the motor's rotor (armature) rotates, its coils move through the stationary magnetic field produced by the stator. According to Faraday’s law of induction, this motion causes the magnetic flux through the coils to change over time, which induces an electromotive force (voltage) within the winding.134

This generated voltage is directly proportional to the speed of the rotor. Because of Lenz’s law, this induced voltage acts in opposition to the source voltage that is driving the motor. As the motor's speed increases, the magnitude of this back voltage rises, which effectively reduces the net voltage across the armature, thereby limiting the current and the resulting torque. Consequently, the back voltage serves as a self-regulating mechanism that prevents the motor from drawing excessive current once it reaches its operating speed.142