What is the purpose of gearing between a motor and a load?

• A. To increase the motor's electrical efficiency without changing speed.
• B. To convert AC to DC.
• C. To measure torque.
• D. To modify speed and torque to match load requirements; higher gear ratio increases torque at the expense of speed.

Answer: (D)

Gearing between a motor and a load is used to tailor the output to what the load actually requires. Motors often run fast but don’t always have enough torque at that speed to move a heavy or resistant load, so a gearbox helps match performance to demand. A gear reduction increases the torque available at the output while reducing the output speed. The trade-off comes from power balance: output torque is roughly input torque multiplied by the gear ratio (minus losses), and output speed is the input speed divided by the gear ratio. So a higher gear ratio makes the driven shaft stronger (more torque) but slower, which is exactly what you need for starting, lifting, or moving heavy loads. Conversely, a smaller ratio keeps speed higher but torque lower, suitable for lighter loads. The other ideas don’t fit because gearing doesn’t change electrical efficiency, convertAC to DC, or measure torque directly.