Hysteresis motor is particularly useful for high-quality record players and tape-recorders because

The correct answer is D. Hysteresis motors develop hysteresis torque which is extremely steady both in amplitude and phase.

Hysteresis motors are particularly useful for high-quality record players and tape-recorders because they are able to produce a very smooth and consistent rotation. This is due to the fact that the hysteresis torque is not affected by changes in the load or the speed of the motor. As a result, hysteresis motors are ideal for applications where a high degree of accuracy is required, such as in the playback of audio recordings.

The other options are not correct because:

• Option A is incorrect because hysteresis motors do not revolve synchronously. They revolve at a speed that is determined by the load on the motor.
• Option B is incorrect because hysteresis motors are subject to magnetic and mechanical vibrations. However, these vibrations are typically very small and do not affect the performance of the motor.
• Option C is incorrect because hysteresis motors are not easily manufactured in extremely small sizes. They are typically manufactured in sizes that are larger than 1 W output.