Module 2 : Electrostatics
Lecture 6 : Quantization Of Charge
  COULOMB's LAW
Coulomb's law is the fundamental law of electromagnetism. It gives the force between two charges $Q_1$ and $Q_2$, separated by a distance $r$. The features of the force are :
proportional to the product of the charges (like charges repel and unlike charges attract),
inversely proportional to the square of the distance between them,
is central in nature
  Mathematically, the force on $Q_2$ due to $Q_1$
 
\begin{displaymath}F_{21} \propto \frac{Q_1Q_2}{r^2}\hat r\end{displaymath}
  $\hat r$ is a unit vector from $Q_1$ to $Q_2$.   We can write
 
\begin{displaymath}F_{21}= \frac{1}{4\pi\epsilon_0} \frac{Q_1Q_2}{r^2}\hat r\end{displaymath}
  $\epsilon_0$ is called permittivity of free space. In SI units, its value is
 
\begin{displaymath}\epsilon_0 = 8.85\times 10^{-12}\;\;\; \frac{{\rm coul}^2}{{\rm N.m}^2}\end{displaymath}
  Approximately,
 
\begin{displaymath}\frac{1}{4\pi\epsilon_0}\approx 8.99\times 10^9\;\;\; \frac{{\rm N.m}^2} {{\rm coul}^2}\end{displaymath}
   
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