# RMS or Effective Voltage

August 2nd Fact-of-the-DayThe amount of power
being delivered to a DC circuit load can be calculated easily by
dividing the load resistance into the applied DC voltage squared. However,
power calculation is more complicated in an AC circuit, because the voltage
level continually changes throughout each AC cycle. Power calculation
based on peak AC voltage would be too high, because peak positive and
negative voltages are each reached only for an instant during each cycle.
Power calculation based upon a voltage midway between one peak and zero
also would be wrong, because AC voltage generally changes sinusoidally
from zero to peak, rather than linearly. The voltage value that gives
the correct power result is called the 'Effective Voltage,' because it
is has the same effect on a power calculation as does a DC voltage of
the same value. Effective Voltage is equal to the square root of the mean
value of the squares of all the instantaneous values of an AC voltage.
Because of that, Effective Voltage is also known as the Root Mean Square
or RMS Voltage. *©2005 Martek International All rights reserved.*

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