Question

What is an electric current that reverses its direction in a regular pattern?

Answer 1

Such currents are termed as alternating currents and vary sinusoidally with time.

Depending on whether the circuit is predominantly capacitative or inductive, there may be a phase difference between the voltage and the current : The current may lead or it may lag behind the voltage.
Such things are not observed in direct current circuits.

The voltage `v` is given as,

`v = v""_0Sin omegat`
Where `omega` is the angular frequency such that `omega = 2pinu` and `t` is the time. `v""_0` is the peak voltage.

The current is given by,

`i = i""_0Sin (omegat + phi)`, where `phi` is the phase difference, negative or positive. `i""_0` is the peak current.