When direct current is considered the voltage and current are constant and there is no problem in specifying their magnitude but when an alternating current is considered both alternating voltage and current varies from instant to instant and that possess problem how to specify the magnitude of the voltage and current. Voltage and current can be expressed in peak mean maximum current or effective value known as RMS. It is stated that specifying an alternating voltage or current its peak which is also known as maximum value is rarely used as it has value only twice its cycle. On the other hand average or mean value can not be used as it is positive as much as it is negative and that is why the average value is zero.
What is average value of alternating current?
The average value of alternating current is also called mean value of the current and it is equal to the value of direct current which transfers across any circuit the same charge as it transferred by the alternating current. In case of the one whose two half-cycles are similar there the average or mean value over a cycle is zero for such alternating quantities mean value means the value determined by taking average of the instantaneous during the half-cycle on the other hand unsymmetrical alternating current are determined as half-wave rectified current where average value means the value taking into consideration whole cycle. These can be applicable on the half-cycle as well but there is no need to find the average or mean value so that the half cycle can be determined without disturbing the components of the whole current cycle.
What is meant by RMS value or effective value of alternating current?
The arms value is somehow also known as the effective value of the alternating current and it is given by the steady current or voltage which flows to a given resistance for a given time which produces the same amount of heat when the alternating voltage is applied to the same resistance for the same time. It is considered that the effective value or virtual value of alternating voltage somehow equals to the square root of the mean of squares successive ordinates and that is the reason why it is also known as root mean square value which is the full form of rms.