Question
In order to measure the internal resistance r 1 of a cell of emf ε , a meter bridge of wire resistance R 0 = 50   Ω , a resistance R 0 2 , another cell of emf ε 2 (internal resistance r ) and a galvanometer G are used in a circuit, as shown in the figure. If the null point is found at l = 72   cm , then the value of r 1 = _ _ _ _ Ω .