The variation with time 
of the current 
in a resistor is shown in the figure below.
The variation of the current with time is sinusoidal.
Explain why, although the current is not in one direction only, power is converted in the resistor.
Using the relation between root-mean-square (r.m.s.) current and peak current, deduce the value of the ratio
does not depend on the direction of the current 
according to the formula of power which is given as
is the resistance of the resistor.
