Alternating current is a current which changes direction and instantaneous value with time.

When using an AC supply, the voltage and current of the system will increase to reach a peak and decrease to reach a trough, instead of remaining at one constant value the way they would using a DC supply. The effective current and voltage, i.e. the root mean square, can be calculated using the peak.

When using a circuit where current only flows in one direction — e.g. an LED that only conducts when forward biased — the oscilloscope trace for an AC supply becomes a half wave rectification diagram.

The following relationships links the root mean square (rms) and peak values of voltage and current and can be used to solve problems involving those quantities.

$$ V_{rms}=\dfrac{V_{peak}}{\sqrt{2}} $$

$$ I_{rms}=\dfrac{I_{peak}}{\sqrt{2}} $$

The rms and peak values, as well as the frequency and period of the wave produced by an AC signal (as related in the below formula), can be determined from graphical data.

$$ T=\dfrac{1}{f} $$