- The maximum potential difference supplied by an a.c source is known as the peak voltage V
_{P}. - The effective potential difference for an a.c is equal to the potential difference of a alternating current if both results in the same heating effect.
- The effective potential difference for a.c is known as the root mean square voltage (r.m.s) of the a.c. and is given y the following equation:

$${V}_{rms}=\frac{{V}_{p}}{\sqrt{2}}$$

- The root-mean-square (r.m.s) value of an alternating current is the value of the steady direct current which produces the same power in a resistor as the mean power produced by the alternating current.
- The r.m.s current is the effective value of the alternating current.
- The r.m.s. current can be calculated by using the following equation:

**Example 1**

Diagram above shows a graph of potential difference, V against time, t of an alternating current. Find the V

_{r.m.s}. of the power supply.

**Answer**:

$$\begin{array}{l}{V}_{rms}=\frac{{V}_{p}}{\sqrt{2}}\\ {V}_{rms}=\frac{(14)}{\sqrt{2}}=9.90V\end{array}$$

**Example 2**

The diagram above shows the wave form of an a.c. supply. What is the root mean square value of the current?

**Answer**:

$$\begin{array}{l}{I}_{rms}=\frac{{I}_{p}}{\sqrt{2}}\\ {I}_{rms}=\frac{(2)}{\sqrt{2}}=1.41\end{array}$$