In the, Ohm's law experiment to find resistance of unknown resistor `R`, following two arrangement (`a`) and (`b`) are possible.

The resistance measured is given by
`R_(measured)=(V)/(i)`
`V`= voltage reading of voltmeter, `i=` current Reading of ammeter.
But unfortunately the ammeters and voltmeter used are not ideal, but having resistance `R_(A)` and `R_(V)` respectively.
For arrangement (`s`), the measured resistance is

Options

A. `R+R_(V)`
B. `R+R_(A)`
C. `(R R_(V))/(R+R_(V))`
D. `(R R_(V))/(R+R_(V))+R_(A)`

Answer

B

Explanation

Let total current is `I_(0)`. Then in circuit (`a`)

`i=(R_(V))/(R+R_(A)+R_(V))xxI_(0)`
So `(V)/(I)=R+R_(A)=R_("measured")`
in circuit (`b`)

`V=I'xxR_(V)=(R R_(V))/(R+R_(V))xxi`
So `R_(measured)=(R R_(V))/(R+R_(V))`
To measure `x`, circuit (`b`) should be used, as
`R_("measured")=(R R_(V))/(R+R_(V)) gt gt R` as `R gt gt R_(A)`