Performance differences.

Performance differences.

• A. DC motors offer superior starting torque and precise speed control; AC motors are more efficient for constant-speed industrial tasks.
• B. AC motors offer superior starting torque; DC motors are less efficient for constant-speed tasks.
• C. DC motors are more efficient than AC motors at all loads.
• D. AC motors provide higher starting torque and better speed control than DC motors.

Answer: (A)

The main idea is how starting torque, speed control, and efficiency differ between DC and AC motors. DC motors can be controlled directly by changing armature voltage or field current, which lets you vary speed over a wide range and produce high starting torque because the current at zero speed is limited only by the supply and winding design. This gives precise speed control, especially at low speeds, making DC motors well-suited when you need to start heavy loads and regulate speed precisely. AC motors, particularly induction motors, are known for high efficiency and simple, rugged operation with minimal maintenance. Their speed is tied to the supply frequency and is more constant under steady conditions, which makes them excellent for constant-speed industrial tasks. Starting torque in a basic AC induction motor is typically lower than a DC motor unless you add special features (like a variable-frequency drive or a wound-rotor design), but once running, they’re efficient and reliable. Therefore, the statement that DC motors offer superior starting torque and precise speed control, while AC motors are more efficient for constant-speed tasks best captures the general performance differences between the two motor types.

The main idea is how starting torque, speed control, and efficiency differ between DC and AC motors. DC motors can be controlled directly by changing armature voltage or field current, which lets you vary speed over a wide range and produce high starting torque because the current at zero speed is limited only by the supply and winding design. This gives precise speed control, especially at low speeds, making DC motors well-suited when you need to start heavy loads and regulate speed precisely.

AC motors, particularly induction motors, are known for high efficiency and simple, rugged operation with minimal maintenance. Their speed is tied to the supply frequency and is more constant under steady conditions, which makes them excellent for constant-speed industrial tasks. Starting torque in a basic AC induction motor is typically lower than a DC motor unless you add special features (like a variable-frequency drive or a wound-rotor design), but once running, they’re efficient and reliable.

Therefore, the statement that DC motors offer superior starting torque and precise speed control, while AC motors are more efficient for constant-speed tasks best captures the general performance differences between the two motor types.