# 3.5: Frequency and Alternators

- Page ID
- 2645

**cycle** means from the point in a waveform to where the waveform starts to repeat itself. When we discuss the term **frequency**, we are referring to how many cycles can occur in one second. Frequency is measured in **hertz** (shout out to Heinrich Hertz) or **CPS** (cycles per second). Two factors affect the frequency in an alternator: rotation speed and the number of poles.

## Rotation speed

**RPM**. However, we are not concerned with minutes, but rather, with seconds when dealing with frequency. Therefore, RPM must be converted to rotations per second (**RPS**). As there are 60 seconds in a minute, all we have to do is to divide the RPM by 60 to convert it to RPS.

## Number of Poles

## Formula time!

\[ f= \dfrac{P}{2} \times \dfrac{N}{60} \tag{Frequency formula}\]

- \(f\) = frequency in hertz
- \(P\) = number of poles
- \(N\) = rotational speed in RPM

\[f = \dfrac{PN}{120} \tag{Combined frequency formula}\]