Higher Physics a.c. voltages and currents a.c. Voltages and Currents • We know that a.c. stands for alternating current. • An a.c. current is so-called as it continuously changes size and direction. • A voltage that produces such a current is called an a.c. voltage. • When working with a.c. currents and voltages we often need to use a kind of average value. r.m.s. Values • In Higher, we call this ‘average’ the r.m.s. value. • ‘r.m.s.’ stands for ‘root mean square’. • The r.m.s. value of an a.c. current or voltage supply the same amount of energy to a lamp or heater as the equivalent d.c. voltage would do. • 𝑉𝑟𝑚𝑠 = 𝑉𝑑𝑐 Link between peak voltage and rms voltage.