A parallel plate capacitor has circular plates of $10\, cm$ radius separated by an air-gap of $1\, mm$ . It is charged by connecting the plates to a $100\, volt$ battery. Then the change in energy stored in the capacitor when the plates are moved to a distance of $1\, cm$ and the plates are maintained in connection with the battery, is
Loss of $12.5\, ergs$
Loss of $125\,ergs$
Gain of $125\, ergs$
Gain of $12.5\, ergs$
A point charge $q$ is situated at a distance $d$ from one end of a thin non - conducting rod of length $L$ having a charge $Q$ (uniformly distributed along its length) as shown in fig.Then the magnitude of electric force between them is
In an oscillating $LC$ circuit the maximum charge on the capacitor is $Q$. The charge on the capacitor when the energy is stored equally between the electric and magnetic fields is
A series combination of $n_1$ capacitors, each of value $C_1$, is charged by a source of potential difference $4\,V$. When another parallel combination $n_2$ capacitors, each of value $C_2$, is charged by a source of potential difference $V$, it has the same (total) energy store in it, as the first combination has. The value of $C_2$, in terms of $C_1$, is then
Half of the space between parallel plate capacitor is filled with a medium of dielectric constant $K$ parallel to the plates . If initially the capacity is $C$, then the new capacity will be
A total charge $Q$ is broken in two parts $Q_1$ and $Q_2$ and they are placed at a distance $R$ from each other. The maximum force of repulsion between them will occur, when