Two small spheres 18cm apart have equal negative charges and repel each other with the force $6\times {10}^{-8}N$. Find the total charge on two spheres.

Four charges of $+6\times {10}^{-8}C$ each are placed at the corners of a square whose sides are $3 \mathrm{cm}$, each. Calculate the resultant force on each charge and show direction in a diagram drawn to scale.

The electric field in a region is given by  $E=5.0 \mathrm{kN}/\mathrm{C}$. Calculate the electric flux through a square of side $10.0 \mathrm{cm}$ in the following case:

When the square is along the $XY$ plane.

The electric field in a region is given by E$=5.0 \mathrm{kN}/\mathrm{C}$. Calculate the electric flux through a square of side $10.0 \mathrm{cm}$ in the following case: The normal to the square makes an angle of ${45}^0$with the $Z$ axis.

A potential difference of $5000 \mathrm{V}$ is applied between two parallel plates $5 \mathrm{cm}$ apart a small oil drop having a charge of  $9.6\times {10}^{-19} \mathrm{C}$ falls between the plates. Find

(a) electric field intensity between the plates and

(b) the force on the oil drop.