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 (`b`), 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)`

Explanation

Reading of Ammeter = I Reading of voltmeter =P.d across voltmeter =P.d across `(R +R_A)` system `= I `(R +R_(A)`
`rArr` Measured resistance `= (V)/(i) = (i(R+R_(A))/(i) =R +R_(A)`
.