A point charge $q={10}^{-11}C$ is placed at $4 \mathrm{cm}$ above a square plate $\left(8 \mathrm{cm}\times 8 \mathrm{cm}\right)$ having charge density $0.5\times {10}^{-8} \mathrm{C} {\mathrm{m}}^{-2}$. Find the flux related with it.

An electron falls from rest through a vertical distance $h$ in a uniform and vertically upward directed electric field $E$. The direction of electric field is now reversed, keeping its magnitude the same. A proton is allowed to fall from rest in it through the same vertical distance $h$. The time of fall of the electron, in comparison to the time of fall of the proton is 

Two balls each of mass $1 \mathrm{gm}$ are suspended by insulating strings each of $1 \mathrm{m}$. At equilibrium, angle between string and vertical is $30°$. Find charge on any one ball.

A particle is released from rest. in an electric field $\overrightarrow{\mathrm{E}}=5\mathrm{kV}/\mathrm{m} \hat{\mathrm{i}}$. Initially particle is at $\left(0,0\right)$. When displacement in $y$-direction is $84\mathrm{cm}$, then find displacement in $x$-direction.

[$g=9.8 \mathrm{m} {\mathrm{s}}^{-1}$ and $\frac{\mathrm{q}}{\mathrm{m}}=10\mathrm{\mu C}/\mathrm{kg}$

Three charges $-q_1,+q_2$ and $-q_3$ are placed as shown in the figure. The $x$-component of the force on $-q_1$ is proportional to: