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 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 thin disc of radius b=2a has a concentric hole of radius a' in it.It carries uniform charge density sigma on it.If the electric field on its axis at distance 'd' from the centre is given as 'nd' then value of 'n' is

Potential on the axis of ring of radius 3R and at distance 4R from centre of ring is (charge on the ring is Q )

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

A ring has radius 30cm and a charge of 2nC .The electric potential on the axis of the ring at a distance of 40cm from its centre will be

A ring of radius a contains a charge q distributed. uniformly ober its length. Find the electric field at a point. on the axis of the ring at a distance x from the centre.

A conducting sphere A of radius a ,with charge Q , is placed concentrically inside a conducting shell B of radius b . B is earthed. C is the common centre of the A and B

An electron released on the axis of a positively charged ring at a large distance from the centre will