In the potentiometer, when the cell in the secondary circuit is shunted with 4 Ω resistance, the balance is obtained at the length 120 cm of wire.…

In the potentiometer, when the cell in the secondary circuit is shunted with $\displaystyle 4 \Omega$ resistance, the balance is obtained at the length $\displaystyle 120$ cm of wire. Now when the same cell is shunted with $\displaystyle 12 \Omega$ resistance, the balance is shifted to a length of $\displaystyle 180$ cm . The internal resistance of cell is $\displaystyle \_\_\_\_$ $\displaystyle \Omega$