In $Millikan's$ oil drop experiment,a charge $Q$ is held stationary between two plates under a potential difference of $2400\, V$. If a second drop with half the radius is to be held stationary using a potential difference of $600\, V$,then the charge on the second drop is:

$N$ small drops,each of radius $r$,are charged to a potential $V$. If they coalesce to form a single large drop,what is the potential of the large drop?

The ratio of potential difference that must be applied across parallel and series combination of two capacitors $C_1$ and $C_2$ with their capacitance in the ratio $1: 2$ so that energy stored in these two cases becomes same is

Five identical capacitors, each of capacitance $20 \mu F$, are connected to a battery of $150 V$ in the combination shown in the diagram. What is the total amount of charge stored?

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 . . . . . . .

Find the heat produced in the capacitors on closing the switch $S$. (in $J$)