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.