A potentiometer wire of length 1 m and resistance $10 \Omega$ is connected in series with a cell of e.m.f 2V with internal resistance $ 1 \Omega $ and a resistance box of a resistance R if potential difference between ends of the wire is 1V the value of R is.
$ I = { E \over x + R+r} = { 2 \over 10+R+1} = { 2 \over 11+R} $ $ \Rightarrow V = I \times X $ $ Or I = { 2 \over 11 + R } \times 10 = { 20 \over 11+R} $ $ Or 11 + R = 20 $ $ R = 20 -11 = 9 \Omega $