What is the role of PWM in motor speed control?

• A. PWM increases instantaneous voltage.
• B. PWM simply changes color of LED.
• C. PWM controls the average voltage by adjusting duty cycle.
• D. PWM changes the motor's physical size.

Answer: (C)

Pulse-width modulation controls the average voltage delivered to a motor by adjusting how long the switch stays on during each cycle (the duty cycle). The motor is fed with full voltage while the switch is on and zero voltage when it’s off, so the effective voltage the motor sees is Vavg = Vin × duty cycle. By increasing the duty cycle, you raise the average voltage and speed; decreasing it lowers the average voltage and slows the motor. The motor’s inductance smooths the current, so speed changes feel gradual and efficient, with less wasted heat than a linear regulator. This isn’t about increasing instantaneous voltage, changing LED color, or altering the motor’s size.