A potentiometer wire 10 long has a resistance of `40Omega`. It is connected in series with a resistances box and a 2 v storage cell. If the potential gradient along the wire is `0.01(V)/(m)` the resistance unplugged in the box is

Options

A. `260 Omega`
B. `760 Omega`
C. `960 Omega`
D. `1060 Omega`

Answer

B

Explanation

Potential gradient =`0.1 xx 10^(-3) V//cm`
`(l xx 40)/1000 = 0.1 xx 10^(-3) rArr l =1/400 A`
`2/(40 +R) = 0.1 xx 10^(-3) rArr l = 1/400 A`
`2/(40 + R) = 1/400 rArr 40 + R = 800 rArr R = 760 Omega`