In a.c. the magnitude and direction is changing continuously. During one half cycle it is in one direction and during next half cycle it is in reverse direction. So average current is zero, hence ordinary moving coil galvanometers cannot be used for measuring a.c. current and voltage. For measuring a.c. current and voltage, hot wire meters are used which are based.pn the heating effect of current. These meters measure virtual value of alternating current and voltage.
