One metallic sphere A is given positive charge whereas another identical metallic sphere B of exactly same mass as of A is given equal amount of negative charge. Then 

(1) Mass of A and mass of B is the same

(2) Mass of A is more

(3) Mass of B is less

(4) Mass of B is more

A point charge q is placed over a horizontal square of side L at a normal distance of L/4 from its centre. Electric flux through the square is 

1. $\mathrm{\varphi }=\frac{\mathrm{q}}{6{\mathrm{\epsilon }}_0}$

2. $\mathrm{\varphi }<\frac{\mathrm{q}}{6{\mathrm{\epsilon }}_0}$

3. $\frac{\mathrm{q}}{6{\mathrm{\epsilon }}_0}<\mathrm{\varphi }<\frac{\mathrm{q}}{{\mathrm{\epsilon }}_0}$

4. $\mathrm{\varphi }>\frac{\mathrm{q}}{6{\mathrm{\epsilon }}_0}$

Consider the charge configuration and spherical Gaussian surface as shown in the figure. When calculating the flux of the electric field over the spherical surface, the electric field will be due to:

An electron enters an electric field with its velocity in the direction of the electric lines of force. Then 

(1) The path of the electron will be a circle

(2) The path of the electron will be a parabola

(3) The velocity of the electron will decrease

(4) The velocity of the electron will increase

A point charge of 40 stat coulomb is placed 2 cm in front of an earthed metallic plane plate of large size. Then the force of attraction on the point charge is

(1) 100 dynes

(2) 160 dynes

(3) 1600 dynes

(4) 400 dynes

Two infinitely long parallel wires having linear charge densities λ₁ and λ₂ respectively are placed at a distance of R meters. The force per unit length on either wire will be $\left(K=\frac{{\displaystyle 1}}{{\displaystyle 4\pi {\epsilon }_0}}\right)$

(1) $K\frac{2{\lambda }_1{\lambda }_2}{R^2}$

(2) $K\frac{2{\lambda }_1{\lambda }_2}{R}$

(3) $K\frac{{\lambda }_1{\lambda }_2}{R^2}$ 

(4) $K\frac{{\lambda }_1{\lambda }_2}{R}$

A solid conducting sphere of radius a has a net positive charge 2Q. A conducting spherical shell of inner radius b and outer radius c is concentric with the solid sphere and has a net charge –Q. The surface charge density on the inner and outer surfaces of the spherical shell will be 

(1) $-\frac{2Q}{4\pi b^2},\frac{Q}{4\pi c^2}$

(2) $-\frac{Q}{4\pi b^2},\frac{Q}{4\pi c^2}$

(3) $0,\frac{Q}{4\pi c^2}$

(4) None of the above

Two equal charges are separated by a distance d. A third charge placed on a perpendicular bisector at x distance will experience maximum coulomb force when 

(1) $x=\frac{d}{\sqrt{2}}$

(2) $x=\frac{d}{2}$

(3) $x=\frac{d}{2\sqrt{2}}$

(4) $x=\frac{d}{2\sqrt{3}}$

An electron is moving around the nucleus of a hydrogen atom in a circular orbit of radius \(r\). The Coulomb force $\overrightarrow{F}$ on the electron is: (Where $K=\frac{1}{4\pi {\epsilon }_0}$) 
1. $-K\frac{e^2}{r^3}\hat{r}$
2. $K\frac{e^2}{r^3}\overrightarrow{r}$
3. $-K\frac{e^2}{r^3}\overrightarrow{r}$
4. $K\frac{e^2}{r^2}\hat{r}$

F_g and F_e represents gravitational and electrostatic force respectively between electrons situated at a distance 10 cm. The ratio of F_g/ F_e is of the order of 

(1) 10⁴²

(2) 10

(3) 1

(4) 10^–43