In ac,the voltage magnitude and direction is constantly changing.

The voltage(magnitude and direction) can be represented by means of a graph.

The top quadrant represents voltage in one direction and the bottom quadrant represents voltage in the other direction.

The V_{max} represents the highest value the voltage would reach (the blue line).

Since the voltage magnitude is always changing,
it is necessary to identify an average voltage, or a dc equivalent.

This avearge value is called the average voltage or I_{rms} (the green line). This is called root mean square, which is really a
complicated way of saying "average".
How do the numbers work?

Easy!
Assume that V_{max} = 300V.

(This would be the peak on the graph)

Calculate the average, V_{rms}.

**Equation**

300 = 1,41(V_{rms})

I_{rms} = 212,77V

You must learn the above equation.