Definition of Electrostatic
The study of electric charges at rest under the action of electric forces is known as electrostatics.
Electrostatic Force
An electric force is the force which holds the positive and negative charges that make up atoms and molecules. The human body is composed entirely of atoms and molecules, thus we owe our existence to the electric force.
Nature of Charges
We know that there are two kinds of charges, namely, positive and negative charges. The charge on an electron is assumed to be negative and charge on a proton is positive.
Properties of Charges
We know that like charges repel each other and unlike charges attract each other. Now we investigate the quantitative nature of these forces. The first measurement of the force between electric charges was made in 1874 AD by Charles Coulomb, a French military engineer. On the basis of these measurements, he deduced a law known as Coulomb's law.
COULOMB'S LAW
The force between two point charges is directly proportional to the product of the magnitudes of charges and inversely proportional to the square of the distance between them.
It is mathematically expressed as
F ∝ q1 q2
F ∝ 1/r
where F is the magnitude of the mutual force that acts on each of the two point charges q1 q2 and r is the distance between them. The force F always acts along the line joining the two point charges, k is the constant of proportionality. Its value depends upon the nature of medium between the two charges and system of units in which F, q and r are measured. If the medium between the two point charges is free space and the system of units is SI, then k is represented as
where ε0 is an electrical constant, known as permittivity of free space. In SI units, its value is
Substituting the value of ε, the constant
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