electrostatics Questions

If the electric flux entering and leaving an enclosed surface respectively is ${\varphi }_1$ and ${\varphi }_2$, the electric charge inside the surface will be:

Three charges $-q_1$, $+q_2$ and $-q_3$ are placed as shown in the figure. ($-q_1$ at origin, $+q_2$ at $(b,0)$, $-q_3$ at $(a\cos \theta ,a\sin \theta )$). The $x$ -component of the force on $-q_1$ is proportional to:

The work done in placing a charge of $8\times 10^{-18}$ coulomb on a condenser of capacity $100$ micro-farad is:

A sheet of aluminium foil of negligible thickness is introduced between the plates of a capacitor. The capacitance of the capacitor:

A thin spherical conducting shell of radius $R$ has a charge $q$. Another charge $Q$ is placed at the centre of the shell. The electrostatic potential at a point $P$ at a distance $R/2$ from the centre of the shell is: