The correct answer is: C. between 9 to 16.
The number of slots per pole in a DC machine is usually between 9 and 16. This is because the number of slots per pole affects the performance of the machine. A higher number of slots per pole will result in a smoother torque output, but it will also make the machine more expensive to manufacture. A lower number of slots per pole will result in a less smooth torque output, but it will also make the machine less expensive to manufacture.
The number of slots per pole is also affected by the type of DC machine. For example, a DC motor with a commutator will have a different number of slots per pole than a DC generator.
The following are the brief explanations of each option:
- Option A: Between 2 to 4. This is not a common number of slots per pole for a DC machine. Most DC machines have a number of slots per pole that is greater than 4.
- Option B: Between 6 to 8. This is a common number of slots per pole for a DC machine. However, it is not the most common number of slots per pole.
- Option C: Between 9 to 16. This is the most common number of slots per pole for a DC machine. It provides a good balance between performance and cost.
- Option D: Between 20 to 30. This is not a common number of slots per pole for a DC machine. Most DC machines have a number of slots per pole that is less than 20.