If $E$ is the electric field intensity of an electrostatic field, then the electrostatic energy density is proportional to

In a uniform electric field, a cube of side $1\ cm$ is placed. The total energy stored in the cube is $8.85\mu J$ . The electric field is parallel to four of the faces of the cube. The electric flux through any one of the remaining two faces 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 of $n_2$ capacitors, each of value $C_2,$ is charged by a source of potential difference $V$, it has the same (total) energy stored in it, as the first combination has. The value of $C_2,$ in terms of $C_1$ is then

The energy stored in a condenser of capacity $C$ which has been raised to a potential $V$ is given by

A capacitor with capacitance $5\,\mu F$ is charged to $5\,\mu C.$ If the plates are pulled apart to reduce the capacitance to $2\,\mu F,$ how much work is done?