Four charges are arranged at the corners of a square ABCD, as shown in the adjoining figure. The force on the charge kept at the centre O is:

      

1.	Zero	2.	Along the diagonal AC
3.	Along the diagonal BD	4.	Perpendicular to side AB

In the absence of other conductors, the surface charge density

(1) Is proportional to the charge on the conductor and its surface area

(2) Inversely proportional to the charge and directly proportional to the surface area

(3) Directly proportional to the charge and inversely proportional to the surface area

(4) Inversely proportional to the charge and the surface area

Out of gravitational, electromagnetic, Vander Waals, electrostatic and nuclear forces; which two are able to provide an attractive force between two neutrons 

(1) Electrostatic and gravitational

(2) Electrostatic and nuclear

(3) Gravitational and nuclear

(4) Some other forces like Vander Waals

Three charges \(4q,Q,\) and \(q\) are in a straight line in the position of \(0,l/2,\) and \(l\) respectively. The resultant force on \(q\) will be zero if \(Q\) equal to:
1. \(-q\)
2. \(-2q\)
3. \(\frac{-q}{2}\)
4. \(4q\)

Two small spheres each having the charge +Q are suspended by insulating threads of length L from a hook. If this arrangement is taken in space where there is no gravitational effect, then the angle between the two suspensions and the tension in each will be:

1. ${180}^o,$ $\frac{1}{4\pi {\epsilon }_0}\frac{Q^2}{{\left(2L\right)}^2}$

2. ${90}^o,$ $\frac{1}{4\pi {\epsilon }_0}\frac{Q^2}{L^2}$

3. ${180}^o,$ $\frac{1}{4\pi {\epsilon }_0}\frac{Q^2}{2L^2}$

4. ${180}^o,$ $\frac{1}{4\pi {\epsilon }_0}\frac{Q^2}{L^2}$ 

Two charges each of 1 coulomb are at a distance 1 km apart, the force between them is 

(1) 9 × 10³ Newton

(2) 9 × 10^–3 Newton

(3) 1.1 × 10^–4 Newton

(4) 10⁴ Newton

Two charges \(+2\) C and \(+6\) C are repelling each other with a force of \(12\) N. If each charge is given \(-2\) C of charge, then the value of the force will be:

The dielectric constant of pure water is 81. Its permittivity will be:

1. 7.12 × 10^–10 MKS units

2. 8.86 × 10^–12 MKS units

3. 1.02 × 10¹³ MKS units

4. Cannot be calculated

Force of attraction between two point charges Q and – Q separated by d meter is F_e. When these charges are given to two identical spheres of radius R = 0.3 d whose centres are d meter apart, the force of attraction between them is 

1. Greater than F_e

2. Equal to F_e

3. Less than F_e

4. None of the above

One metallic sphere A is given a positive charge whereas another identical metallic sphere B of the exact same mass as of A is given an equal amount of negative charge. Then:

(1) mass of A and mass of B are the same.

(2) mass of A is more.

(3) mass of B is less.

(4) mass of B is more.