Ncert Exercises & Solutions

When a voltage measuring device is connected to AC mains, the meter shows the steady input voltage of \(220~\text{V}\). This means:

1.	input voltage cannot be AC voltage, but a DC voltage
2.	maximum input voltage is \(220~\text{V}\)
3.	the meter reads not v but \(<v^2>\) and is calibrated to read \(\sqrt{<v^2>}\)
4.	the pointer of the meter is stuck by some mechanical defect

The voltmeter connected to AC mains reads mean value (

< v^{2} >

) and is calibrated in such a way that it gives the value of

< v^{2} >

, which is multiplied by form factor to give RMS value.