Electric Charges and Fields · Question 10

Two point charges A and B, having charges +Q and -Q respectively, are placed at certain distance apart and force acting between them is F. If 25% charge of A is transferred to B, then force between the charges becomes :

1. F
2. 16F9
3. 9F16
4. 4F3

Two parallel infinite line charges with linear charge densities + C/m and - C/m are placed at a distance of 2R in free space. What is the electric field mid-way between the two line charges?

1. 2 0R N/C
2. zero
3. 0R N/C
4. 2 0R N/C

An electron falls from rest through a vertical distance h in a uniform and vertically upward directed electric field E. The direction of electric field is now reversed, keeping its magnitude the same. A proton is allowed to fall from rest in it through the same vertical distance h. The time of fall of the electron, in comparison to the time of fall of the proton is

1. smaller
2. 5 times greater
3. 10 times greater
4. equal

Suppose the charge of a proton and an electron differ slightly. One of them is -e, the other is (e + e). If the net of electrostatic force and gravitational force between two hydrogen atoms placed at a distance d (much greater than atomic size) apart is zero, then e is of the order of [Given : mass of hydrogen mh = 1.67 10-27 kg]

1. 10-23 C
2. 10-37 C
3. 10-47 C
4. 10-20 C

Two identical charged spheres suspended from a common point by two massless strings of lengths l, are initially at a distance d (d l) apart because of their mutual repulsion. The charges begin to leak from both the spheres at a constant rate. As a result, the spheres approach each other with a velocity v. Then v varies as a function of the distance x between the spheres, as

1. v x-1/2
2. v x-1
3. v x1/2
4. v x

An electric dipole is placed at an angle of 30 with an electric field intensity 2 105 N C-1. It experiences a torque equal to 4 N m. The charge on the dipole, if the dipole length is 2 cm, is

1. 8 mC
2. 2 mC
3. 5 mC
4. 7

The electric field in a certain region is acting radially outward and is given by E = Ar. A charge contained in a sphere of radius 'a' centred at the origin of the field, will be given by

1. 4 0 Aa3
2. 0 Aa3
3. 4 0 Aa2
4. A 0 a2

Two pith balls carrying equal charges are suspended from a common point by strings of equal length, the equilibrium separation between them is r. Now the strings are rigidly clamped at half the height. The equilibrium separation between the balls now becomes [figure]

1. ( 2r 3 )
2. ( 2r3 )
3. ( 1 2 )2 r
4. ( r [3]2 )

A charge q is placed at the centre of the line joining two equal charges Q. The system of the three charges will be in equilibrium if q is equal to

1. -Q/4
2. Q/4
3. -Q/2
4. Q/2

What is the flux through a cube of side a if a point charge of q is at one of its corners?

1. 2q 0
2. q8 0
3. q 0
4. q2 06a2