Two small identical spheres, each of mass $1 \mathrm{g}$ and carrying the same charge ${10}^{-9} \mathrm{C}$ are suspended by threads of equal lengths. If the distance between the centres of the spheres is $0.3 \mathrm{cm}$ in equilibrium then the inclination of the thread with the vertical will be:

A nonconducting solid sphere of radius $R$ is charged uniformly. The magnitude of the electric field due to the sphere at a distance $r$ from its centre :

(a) increases as $r$ increases, for $r<R$

(b) decreases as $r$ increases, for $0<r<$ 

(c) decreases as $r$ increases, for $R<r<$ 

(d) is discontinuous at $r=R$

Electric charge is uniformly distributed over a long straight wire of radius 1 mm. The charge per cm length of the wire is Q coulombs. A cylindrical surface of radius 50 cm and length 1m encloses the wire symmetrically as shown in fig.

The total flux passing through the cylindrical surface is:

Gauss law is given by ${\in }_0\oint \overrightarrow{E}.\overrightarrow{ds}=q,$ if net charge enclosed by Gaussian surface is zero then-.