🔍 Key Concepts

• Difference between AC motors and DC motors in how speed is controlled • Relationship between synchronous speed and frequency for AC motors • Why changing voltage vs. changing frequency affects torque versus speed

💭 Think About

• Ask yourself: For an AC motor, what electrical quantity directly determines its synchronous speed? • Think about which control method is most efficient and commonly used on modern diesel-electric ships with large propulsion motors. • Consider: Does changing voltage alone normally change the speed of an AC motor significantly, or does it mainly affect the motor’s torque and ability to carry load?

✅ Before You Answer

• Recall the formula for synchronous speed of an AC motor and identify which variable you can adjust from the generator or drive system. • Verify which option refers to frequency rather than voltage or current. • Make sure you distinguish between typical control of DC motors (armature voltage/current) and AC propulsion motors (frequency-based control).