Root Mean Square Value (RMS Value)
The Root Mean Square Value (RMS Value) of an alternating current is given by that steady (d.c.) current which when flowing through a given circuit for a given time produces the same heat as produced by the alternating current when flowing through the same circuit for the same time.
Root Mean Square Value (RMS Value) is also known as the effective or virtual value of the alternating current, the former term being used more extensively. For computing the Root Mean Square Value (RMS Value) of symmetrical sinusoidal alternating currents, either mid-ordinate method or analytical method may be used, although for symmetrical but non-sinusoidal waves, the mid-ordinate method would be found more convenient.
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A simple experimental arrangement for measuring the equivalent d.c. value of a sinusoidal current is shown in Figure A. The two circuits have identical resistances but one is connected to battery and the other to a sinusoidal generator. Wattmeters are used to measure heat power in each circuit. The voltage applied to each circuit is so adjusted that heat power production in each circuit is the same. In that case, the direct current will equal Im/√2 which is called Root Mean Square Value (RMS Value) of the sinusoidal current.
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