Question

A generator's maximum output is 220 V. What is the rms potential difference?

Answer 1

The rms potential difference is defined as the peak value of the potential difference divided by the square root of 2:
$V_{rms} = \frac{V_0}{ \sqrt{2} }$
where
$V_0$ is the peak value of the voltage (the maximum voltage).

The generator in our problem has a maximum voltage of $V_0=220 V$, so its rms potential difference is
$V_{rms}= \frac{V_0}{ \sqrt{2} }=155.6 V$