Electrical Engineering ⇒ Topic : R.M.S. or Effective Value

David
 
R.M.S. or Effective Value The average value cannot be used to specify a sinusoidal voltage or current. It is because its value over onecycle is zero and cannot be used for power calculations. Therefore, we must search for a more suitable criterion to measure the effectiveness of an alternating current (or voltage). The obvious choice would be to measure it in terms of direct current that would do work (or produce heat) at the same average rate under similar conditions. This equivalent direct current is called the rootmeansquare (rm. s.) or effective value of alternating current. The effective or r.m.s. value of an alternating current is that steady current (d.c.)which when flowing through a given resistance for a given time produces the same amount of heat as produced by the alternating current when flowing through the same resistance for the same time.For example, when we say that the rm. s. or effective value of an alternating current is 5A, it means that the alternating current will do work (or produce heat) at the same rate as 5A direct current under similar conditions.  
 
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