Two concentric coplanar rings one of radius a and the other of radius 2a, have charges qa and qb respectively. A charged particle is in equilibrium on their common axis at a distance a from the common centre. Then the ratio qa/qb is

Two concentric rings, one of radius a and the other of radius b, have the charges +q, and -(2//5)^(-3//2)q , respectively as shown in fig. Find the rario b//a if a charge particle palaced on the axis at z =a is i equilibrium.

Two concentric spheres of radii R and 2R are charged. The inner sphere has a charge if 1muC and the outer sphere has a charge of 2muC of the same sigh. The potential is 9000 V at a distance 3R from the common centre. The value of R is

An annular disc of inner radius a and outer radius '2a' is uniformly charged with uniform surface charge density sigma . Find the potential at a distance 'a' from the centre at a point 'P' lying on the axis.

Two concentric rings, one of radius R and total charge +Q and second of radius 2R and total charge -sqrt(8)Q , lie in x-y plane (i.e., z=0 plane). The common centre of rings lies at origin and the common axis coincides with z -axis. The charge is uniformly distributed on both rings. At what distance from origin is the net electric field on z -axis zero?

A small conducting spherical shell with inner radius a and outer radius b is concentric with a larger conducting spherical shell with inner radius c and outer radius d. The inner shell has total charge +2q, and the outer shell has charge +4q. (K=(1)/(4piepsilon_(0))) Find the electric field in terms of q and the distance r from the common centre of the two shells for (i) b lt r lt c (ii) c lt r lt d

A small conducting spherical shell with inner radius a and outer radius b is concentric with a larger conducting spherical shell with inner radius c and outer radius d. The inner shell has total charge +2q, and the outer shell has charge +4q. (K=(1)/(4piepsilon_(0))) Find the electric in terms of q and the distance r from the common centre of the two shells for r gt d .

Two soap bubbles, one of radius 50 mm and the other of radius 80 mm , are brought in contact so that they have a common interface. The radius of the curvature of the common interface is

The electrostatic potential of a uniformly charged thin spherical shell of charge Q and radius R at a distance r from the centre

For a uniformly charged ring of radius R, the electric field on its exis has the largest magnitude at a distance h from its centre. Then value of h is :

Two metal spheres, one fo radius R and the other of radius 2R, both have same surface charge density s. They are brought in contact and seprated. What will be new surface charge densitites on them ?