JEE Main 2022 · 30 Jun · Shift 1, Physics question 56

The circuit diagram of potentiometer used to measure the internal resistance of a cell (E) is shown in figure. The key 'K' is kept closed so as to send constant current through potentiometer wire. When key '$K_1$' is kept open the null point is found to be at 120 cm on the potentiometer wire. When the key '$K_1$' is closed the null point is shifted at 80 cm at the potentiometre wire. The internal resistance of the given cell is ______ $\Omega$.