Two small spheres each carrying a charge $q$ are placed $r$ metre apart. If one of the spheres is taken around the other one in a circular path of radius $r$, the work done will be equal to

A condenser having a capacity $2.0$ micro farad is charged to $200\;volts$ and then the plates of the capacitor are connected to a resistance wire. The heat produced in joules will be

The energy of a charged capacitor resides in

A fully charged capacitor has a capacitance $‘C’$. It is discharged through a small coil of resistance wire embedded in a thermally insulated block of specific heat capacity $‘s’$ and mass $‘m’$. If the temperature of the block is raised by ‘$\Delta T$’, the potential difference $‘V’$ across the capacitance is

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

$A$ $2$ $\mu F$ capacitor is charged to a potential $=$ $10\,V$. Another $4$ $\mu F$ capacitor is charged to a potential $=$ $20\,V$. The two capacitors are then connected in a single loop, with the positive plate of one connected with negative plate of the other. What heat is evolved in the circuit?......$\mu J$