The adjacent fig shows a $2.0 \;V$ potentiometer used for the determined of internal resistance of a cell $1.5 \;v$ cell. The balance point of the cell is open circuit is $76.3 \;cm$ . When a resistor of $9.5 \Omega$ is used in the external circuit of the cell, the balance point shifts to $6.48 \;cm$ length of the wire . Determine the internal resistance of the cell
