The mechanical speed of magnetic fields can be related to the electrical frequency and pole number by the formula

The mechanical speed of magnetic fields can be related to the electrical frequency and pole number by the formula:

1. η_m = 120 * f_e * P
2. η_m = 120 * f_e / P
3. η_m = f_e * P / 120
4. η_m = 120 * P / f_e

Correct answer: 2. η_m = 120 * f_e / P