A cell of internal resistance is connected across a resistor. A voltemeter having varible resistance `G` is used to meausre p.d. across resistor. The plot of voltmeter reading `V` against `G` is shown. What is value of external resitor `R`

Options

A. `5Omega`
B. `4Omega`
C. `3 Omega`
D. `1 Omega`

Answer

A

Explanation

`I=(24)/((RG)/(R+G)+1)`
`V=24-` potential difference across `1Omega`
`=24-1xxI`
`V=24-(24)/((1/(1//R)+1/G)+1)`
For G rightarrowinfty Rightarrow `1/G rightarrow 0`
& `V=20V`
`Rightarrow 20=24- (24)/(R+1) Rightarrow R= 5Omega`