Figure shows a large conducting sheet having charge density $\sigma$ on both sheet. The surface potential of sheet is $V_{\mathit{0}}\mathit{.}$ A sphere of radius $\mathrm{r}$ is placed at a distance $\mathrm{\lambda }(\mathrm{\lambda }>>\mathrm{r})$ from the sheet. What will be the value of $\sigma$ on sheet when the key is closed  and charge $\mathrm{q}$ appears on the surface of spher? 

Four point charges $q_A=2 \mu C, q_B=-5 \mu C, q_C=2 \mu C, q_D=-5 \mu C$ are located at the corners of a square $ABCD$ of side $10 \mathrm{cm}.$ The force acting on a charge of $1 \mu \mathrm{C}$ placed at centre of the square is

Three charges are placed at the three vertices of an equilateral triangle of side $a$ as shown in the figure. The force experienced by the charge placed at the vertex $A$ in a direction normal to $BC$ is

Eleven equal point charges, all of them having a charge $+Q,$ are placed at all the hour positions of a circular clock of radius $r$ except at the $10 \mathrm{h}$ position. What is the electric field strength at the centre of the clock?

Shown in the figure is a shell made of a conductor. It has inner radius $a$ and outer radius $b$, and carries charge $Q$ . At its centre a dipole $\overrightarrow{\mathit{p}}$ is placed as shown then:

A uniformly charged solid sphere of radius R has potential $V_0$ (measured with respect to $\infty$ ) on its surface. For this sphere the equipotential surfaces with potential $\frac{3V_0}{2},\frac{5V_0}{4},\frac{3V_0}{4}$ and $\frac{V_0}{4}$ have radius $R_1$ , $R_2, R_3$ and $R_4$ respectively. Then

Note : This question had two option correct at the time of examination. Proper corrections are made in the question to avoid it.