A point charge + q is placed at the midpoint of a cube of side a. The electric flux emerging from the cube is

• zero

• $\frac{3 {\mathrm{qa}}^2}{{\mathrm{\epsilon }}_0}$

• $\frac{\mathrm{q}}{{\mathrm{\epsilon }}_0}$

• $\frac{{\mathrm{\epsilon }}_0}{4{\mathrm{qa}}^2}$

Write down the relation between tesla and gauss. 

The number of electron in 2 coulomb of charge is

• 5 × 10²⁹

• 12.5 × 10¹⁸

• 1.6 × 10¹⁹

• 9 × 10¹¹

Which of the following materials is the best conductor of electricity ?

• Platinum

• Gold

• Silicon

• Copper

A point charge +q is placed at the centre of a cube of side L. The electric flux emerging from the cube is

• $\frac{\mathrm{q}}{{\mathrm{\epsilon }}_0}$

• zero

• $\frac{6{\mathrm{qL}}^2}{{\mathrm{\epsilon }}_0}$

• $\frac{\mathrm{q}}{6{\mathrm{L}}^2{\mathrm{\epsilon }}_0}$

Four charges equal to -Q are placed at the four corners of a square and a charge q is at its centre. If the system is in equilibrium, the value of q is

• $\frac{-\mathrm{Q}}{4}\left(1 + 2\sqrt{2}\right)$

• $\frac{\mathrm{Q}}{4}\left(1 + 2\sqrt{2}\right)$

• $\frac{-\mathrm{Q}}{2}\left(1 + 2\sqrt{2}\right)$

• $\frac{\mathrm{Q}}{2}\left(1 + 2\sqrt{2}\right)$

A charge +q is placed at the origin O of x-y axes as shown in the figure. The work done in taking a charge Q from A to B along the straight line AB is

• $\frac{\mathrm{qQ}}{4{\mathrm{\pi \epsilon }}_0}\left(\frac{\mathrm{a} - \mathrm{b}}{\mathrm{ab}}\right)$

• $\frac{\mathrm{qQ}}{4{\mathrm{\pi \epsilon }}_0}\left(\frac{\mathrm{b} - \mathrm{a}}{\mathrm{ab}}\right)$

• $\frac{\mathrm{qQ}}{4{\mathrm{\pi \epsilon }}_0}\left(\frac{\mathrm{b}}{{\mathrm{a}}^2} - \frac{1}{\mathrm{b}}\right)$

• $\frac{\mathrm{qQ}}{4{\mathrm{\pi \epsilon }}_0}\left(\frac{\mathrm{a}}{{\mathrm{b}}^2} - \frac{1}{\mathrm{b}}\right)$

In a region, the intensity of an electric field is given by E = 2i + 3j+ k in Nc^-1. The electric flux through a surface S = 1Oi m² in the region is

• 5 Nm²C^-1

• 10 Nm²C^-1

• 15 Nm²C^-1

• 20 Nm²C^-1

89.

Two infinite parallel metal planes, contain electric charges with charge densities +σ and -σ respectively and they are separated by a small distance in air. If the permittivity of air is ε₀,then the magnitude of the field between the two planes with its direction will be

• σ/ε₀ towards the positively charged plane

• σ/ε₀ towards the negatively charged plane

• σ/(2ε₀) towards the positively charged plane

• 0 and towards any direction

Two pith balls carrying equal charges are suspended from a common point by strings of equal length, the equilibrium separation between them is r. Now the strings are rigidly clamped at half the height. The equilibrium separation between the balls now become

• ${\left(\frac{1}{\sqrt{2}}\right)}^2$

• $\left(\frac{\mathrm{r}}{\sqrt[3]{2}}\right)$

• $\left(\frac{2\mathrm{r}}{\sqrt{3}}\right)$

• $\left(\frac{2\mathrm{r}}{3}\right)$