The electrostatic force on a small sphere of charge 0.4 µC due to another small sphere of charge –0.8 µC in the air is 0.2 N. The distance between the two spheres is:

1. 14 cm
2. 12 cm
3. 16 cm
4. 10 cm

Dimensional formula of $\frac{k{e}^2}{G{m}_e{m}_p}$ is:
1. [M¹L¹T¹]
2. [M⁰L¹T¹]
3. [M⁰L⁰T⁰]
4. [M^-1L⁰T²]

A system has two charges, \(q_\mathrm{A} = 2.5 \times 10^{-7}~\text{C}\) and \(q_\mathrm{B} = -2.5 \times 10^{-7}~\text{C}\), is located at points \(\mathrm{A}\): \((0,0,-15~\text{cm})\) and \(\mathrm{B}\): \((0,0,+15~\text{cm})\) respectively. The electric dipole moment of the system is:

Which of the following statements about electric field lines (due to static charges) is incorrect?

A polythene piece rubbed with wool is found to have a negative charge of \(3 \times10^{-7}~\text{C}.\) Transfer of mass from wool to polythene is:
1. \(0.7\times10^{-18}~\text{kg}\)
2. \(1.7\times10^{-17}~\text{kg}\)
3. \(0.7\times10^{-17}~\text{kg}\)
4. \(1.7\times10^{-18}~\text{kg}\)

Two insulated charged copper spheres \(A\) and \(B\) have their centers separated by a distance of \(50 ~\text{cm}.\) What is the mutual force of electrostatic repulsion if the charge on each is  $\mathrm{}$\(6 . 5 × 10 ^{- 7}~\text C ?\) 
(The radii of \(A\) and \(B\) are negligible compared to the distance of separation.)
1. \(1.52 × 10^{−2}~\text N\)
2. \(3.7 × 10^{−2}~\text N\)
3. \(2.01 × 10^{−2}~\text N\)
4. \(2.23 × 10^{−1}~\text N\)