Electric Charges and Fields

Two identical conducting spheres P and S with charge Q on each, repel each other with a force 16 N. A third identical uncharged conducting sphere R is successively brought in contact with the two spheres. The new force of repulsion between P and S is :

1. 1 N
2. 6 N
3. 12 N
4. 4 N

In hydrogen like system the ratio of coulombian force and gravitational force between an electron and a proton is in the order of :

1. 1019
2. 1039
3. 1029
4. 1036

The vehicles carrying inflammable fluids usually have metallic chains touching the ground:

1. To protect tyres from catching dirt from ground
2. It is a custom
3. To alert other vehicles
4. To conduct excess charge due to air friction to ground and prevent sparking

An infinitely long positively charged straight thread has a linear charge density Cm-1. An electron revolves along a circular path having axis along the length of the wire. The graph that correctly represents the variation of the kinetic energy of electron as a function of radius of circular path from the wire is :

1. [figure]
2. [figure]
3. [figure]
4. [figure]

A charge q is placed at the center of one of the surfaces of a cube. The flux linked with the cube is:

1. q2 0
2. Zero
3. q4 0
4. q8 0

C1 and C2 are two hollow concentric cubes enclosing charges 2Q and 3Q respectively as shown in figure. The ratio of electric flux passing through C1 and C2 is : [figure]

1. 3:2
2. 5:2
3. 2:5
4. 2:3

Two charges q and 3q are separated by a distance 'r' in air. At a distance x from charge q, the resultant electric field is zero. The value of x is :

1. r3(1+ 3)
2. (1+ 3)r
3. r(1+ 3)
4. r(1+ 3)

Force between two point charges q1 and q2 placed in vacuum at 'r' cm apart is F. Force between them when placed in a medium having dielectric constant K=5 at 'r/5' cm apart will be:

1. 5F
2. 25F
3. F/5
4. F/25

A particle of charge '-q' and mass 'm' moves in a circle of radius 'r' around an infinitely long line charge of linear charge density '+ '. Then time period will be given as : (Consider k as Coulomb's constant)

1. T2= 4 2m2k qr3
2. T= 12 r m2k q
3. T= 12 2k qm
4. T=2 r m2k q

Two charges of 5Q and -2Q are situated at the points (3a,0) and (-5a,0) respectively. The electric flux through a sphere of radius '4a' having center at origin is :

1. 2Q 0
2. 7Q 0
3. 3Q 0
4. 5Q 0

An electric field is given by (6 i+5 j+3 k) N/C. The electric flux through a surface area 30 i m2 lying in YZ-plane (in SI unit) is :

1. 60
2. 90
3. 180
4. 150