The speed of a conventional motor is controlled by the frequency of the current and_______ a. resistance b. voltage c. the load on it d. number of poles

The speed of a conventional motor is controlled by the frequency of the current and the number of poles. So, the correct answer is d. number of poles.

Here's why:

1. The speed of an AC motor is determined by the number of poles it has and the frequency of the power supply, not the voltage or resistance.

2. The number of poles is set when the motor is manufactured and cannot be changed.

3. The frequency of the power supply is typically set by the power company and is usually 50 or 60 Hz, depending on the country.

4. Therefore, the only way to change the speed of the motor is to change the frequency of the power supply, which is usually done with a variable frequency drive.

5. The load on the motor can affect the speed, but it is not a control method. If the load is too high, the motor will slow down, but this is not a desirable situation and can damage the motor.

6. The voltage and resistance do not control the speed of the motor. They can affect the amount of power the motor can produce, but not the speed.