NEIEP Mechanics Practice Exam

How can motor speed be adjusted?

1. By changing the rotor position

2. By varying the field or armature voltage

3. By modifying the load on the motor

4. By changing the type of winding

The correct answer is: By varying the field or armature voltage

Motor speed can be adjusted by varying the field or armature voltage. This method directly impacts the motor's performance because the speed of a motor is fundamentally related to the voltage applied to either the armature or the field winding, especially in DC and certain types of AC motors. By increasing the voltage, more current flows through the windings, which can increase the strength of the magnetic fields involved in operation, thus increasing the motor speed. Conversely, reducing the voltage decreases the current and subsequently slows the motor down. This approach is particularly effective because it allows for fine-tuning of the motor's speed without requiring significant mechanical changes or complex alterations to the motor design. Other methods like changing rotor position or modifying load do not offer as consistent or precise control over the motor speed, as they may result in unintended side effects or inefficiencies. Changing the type of winding is a more permanent alteration to motor design, which isn’t practical for speed adjustment during operation.