A potentiometer wire of length 10 m and resistance 20 Ω is connected in series with a 25 V battery and an external resistance 30 Ω. A cell of emf E…

A potentiometer wire of length $\displaystyle 10$ m and resistance $\displaystyle 20 \Omega$ is connected in series with a $\displaystyle 25$ V battery and an external resistance $\displaystyle 30 \Omega$. A cell of emf E in secondary circuit is balanced by $\displaystyle 250$ cm long potentiometer wire. The value of E (in volt) is $\displaystyle \frac{x}{10}$. The value of $\displaystyle x$ is \_\_\_\_.