Q 1 :    

Three capacitors of capacitances $25$ $\mu F$, $30$ $\mu F$, and $45$ $\mu F$ are connected in parallel to a supply of 100 V. Energy stored in the above combination is E. When these capacitors are connected in series to the same supply, the stored energy is $\frac{9}{x}E$. The value of $x$ is _______ .               [2024]