31. Alternating Current

The current in an AC circuit takes 0.02 s to change direction. What is the angular frequency of the AC source?

An AC source produces an alternating current in a circuit with the function $i\left(t\right)=\left(1.5A\right)\cos \left[\left(250s^{-1}\right)t\right]$. What is the frequency of the source? What is the maximum current in the circuit?