Electric Charges and Fields

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]

An infinite plane sheet of charge having uniform surface charge density + s C/m2 is placed on x-y plane. Another infinitely long line charge having uniform linear charge density + e C/m is placed at z=4 m plane and parallel to y-axis. If the magnitude values | s|=2| e| then at point (0,0,2), the ratio of magnitudes of electric field values due to sheet charge to that of line charge is n:1. The value of n is .

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

Two identical charged spheres are suspended by strings of equal lengths. The strings make an angle with each other. When suspended in water the angle remains the same. If density of the material of the sphere is 1.5 g/cc, the dielectric constant of water will be . (Take density of water = 1 g/cc)

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

Suppose a uniformly charged wall provides a uniform electric field of 2 104 N/C normally. A charged particle of mass 2 g being suspended through a silk thread of length 20 cm and remain stayed at a distance of 10 cm from the wall. Then the charge on the particle will be 1 x μC where x= . [use g=10 m/s2]

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 identical charged spheres are suspended by strings of equal lengths. The strings make an angle of 37 with each other. When suspended in a liquid of density 0.7 g/cm3, the angle remains same. If density of material of the sphere is 1.4 g/cm3, the dielectric constant of the liquid is ( 37 = 34 )