A cell of emf `3.4 V` and internal resistance `3 Omega` is connected to an ammeter having resistance `2Omega` and to an external resistance of `100Omega`. When a voltmeter is connected across the `100 Omega` resistance, the ammeter reading is `0.04 A`. Find the voltage reading by the voltmeter and its resistance. Had the voltmeter been an ideal one what would have been its reading?

Answer

A

Explanation

Reading of voltmeter =3.4-Voltage drop across ammeter and `3Omega` resistance
`=(3.4)-0.04xx2-0.04xx3`
`=3.2V`
Now, `3.2V=((0.04)(100R))/((100+R))`
where R = resistance of voltmeter
`:. R=400 Omega`
If voltmeter is ideal, then
`i=3.4/(2+100+3)=0.03238A`
Reading of voltmeter `=100i=3.238A`