The concept of effective value, the root mean square (RMS) value, is crucial in understanding electrical circuits and power delivery. This idea emerges from the necessity to measure the effectiveness of a voltage or current source in supplying power to a resistive load.

The effective value of a periodic current represents the direct current (DC) that conveys the same average power to a resistor as the periodic current itself. This concept is crucial when assessing AC circuits. To determine the effective value of current, one must find the RMS current, which is the square root of the mean of the squared instantaneous current values over a period. This RMS value corresponds to the DC that delivers the same average power as the periodic current when applied to a resistor.

Similarly, the effective value of voltage is calculated in the same manner as the current. It represents the RMS voltage, essential for assessing power consumption in electrical systems.

The RMS value is a fundamental concept, not limited to sinusoidal signals. For any periodic function, the RMS value is calculated by finding the square of the function, determining the mean of the squares, and then taking the square root of that mean. In practical applications, voltage and current are often expressed in terms of their RMS values rather than peak values. This is because the average value of a sinusoidal signal is zero, making the RMS value a more useful metric for power analysis. As well as this, analog voltmeters and ammeters are designed to directly read the RMS values of voltage and current, making them indispensable tools in power measurements.