PHYSICS & ELECTRONICS / ELECTROMAGNETIC INDUCTION AND AC / PAGE 20 OF 50
The AC Generator and RMS Values
How a rotating coil makes alternating voltage.
A coil rotating in a uniform magnetic field has a sinusoidal EMF induced in it. Slip rings let it connect to the outside circuit, and one full turn of the coil gives one full cycle. Different countries use mains frequencies of 50 Hz or 60 Hz.
Original diagram: the ac generator and rms values
Because AC keeps changing, we quote its RMS value, the steady DC level that would heat a resistor equally. For a sine wave it is the peak value divided by the square root of two.
- Frequency = turns per second.
- Peak voltage is larger than RMS voltage.
- Higher speed or field raises the EMF.
KEY IDEA
V_rms = V_peak / √2Browse all 50 physics and electronics pages | Back to the course index