Question

A symmetrical square-wire voltage is applied to an average reading diode voltmeter having a scale calibrated in terms of rms value of a sine wave, the error in meter indication will be

• A. 1.11 %
• B. 11.1 %
• C. 21.1 %
• D. 0.45 %

Answer 1

The correct option is B 11.1 %

The deflection of the instrument depends upon the average value of current. The form factor of a sinusoidal wave is 1.11 and therefore average value of current fed to the meter for sinusoidal voltage supply is

$I_{av}=\frac{E_{av}}{2R}=\frac{E_{rms}}{2\times 1.11\times R}=0.45\frac{E_{rms}}{R}$

The form factor of a square wave is 1 and with half wave rectification, the average value of current with square wave is

$I_{av}=\frac{E_{av}}{2R}=\frac{E_{rms}}{2\times 1\times R}=0.5\frac{E_{rms}}{R}$

$Percentageerror=\frac{0.5-0.45}{0.45}\times 100=11.1\%$