The emf of the driver cell of a potentiometer is `2 V`, and its internal resistance is negligible. The length of the potentiometer wire is `100 cm`, and resistance is `5 omega`. How much resistance is to be connected in series with the potentiometer wire to have a potential gradient of `0.05 m V cm^(-1)`?

Options

A. `1990 Omega`
B. `2000 Omega`
C. `1995 Omega`
D. none of these

Answer

C

Explanation

`k = 0.05 m vcm^(-1) = 5mVcm^(-1)`
`I = (kl)/(r ) = (5 xx 10^(-3) xx 1)/(5) = 10^(-3) A`
Now, `2 = I(R + r) = 10^(-3) (R + 5)` or `R = 1995 Omega`