question_answer

Direction: A potentiometer is device used for measuring emf and internal resistance of a cell. It consists of two circuits one is main circuit in which there is a cell of given emf\[\varepsilon \] and given resistance R which is connected across a wire of length 100 cm having resistance r. Another circuit having unknown emf\[\varepsilon \]and galvanometer. For a given potentiometer if \[\varepsilon '=30\,V,\,\,r=1\Omega \] and resistance R varies with time t given by\[R=2t\]. The jockey can move on wire with constant velocity 10 cm/s and switch S is closed at\[t=0\].

If jockey starts moving from A at\[t=0\]and balancing point found a\[t=1s,\], then the value of \[\varepsilon \]is

A)  1 V                             

B)  2 V               

C)  3 V                             

D)  4 V