Question

A periodic voltaage waveform observed on oscilloscope of a load is shown in figure.

Which of these given statements(s) is/are correct?

• A. when PMMC voltmeter is connected across load, then it will reads 4 V.
• B. when MI voltmeter is connected across load then it will also reads 4 V.
• C. PMMC instrument always reads rms value.
• D. Moving iron instrument can read only rms value.

Answer 1

Answer: (A), (D)

Moving iron instrument can read only rms value.

When given wave is passed through PMMC, then it will reads average value of waveform

$V_{avg}=\frac{\frac{1}{2}\times 10\times 10-5\times 2+5\times 8}{20}=4volts$

$\Rightarrow$ M.I will reads the rms value, which will be greater than average value for given waveform

$\Rightarrow$ PMMC always reads average value