If you are preparing for enterance exams like AIEEE, IIT-JEE, AIIMS, etc. then your concepts should be very very clear. To clarify your concepts keep answering the questions that will appear in this series of clear your concepts.
1. What is the minimum value of permittivity?
2. What is the minimum value of relative permittivity?
3. Does coulomb force between two charges depends upon the presence of other charges in their neighbourhood?
4. Can the charge distribution be really continuous in strictest sense of term?
5. It is difficult to carry out electrostatic experiments on humid days. Why?
6. A negatively charged rod attracts a suspended object. Can we conclude that the object is positively charged?
7. Repulsion is the sure test of electrification. Explain.
8. Name the properties of charge in which differs from mass.
9. What is the value of 4πε0 ?
10. What is the value of 1/4πεr?