The two
fundamental laws of electronics are as bellow:
1) Like charges
repel each other and unlike charges attract each other.
The law can be
demonstrated by another simple experiment. The ebonite rod becomes negatively
charged when rubbed against fur clot. Now, if glass rod is rubbed against fur
cloth, it gets positively charged. And if they are brought near each other,
they try to attract each other. While two ebonite rods after rubbing against
fur cloth, brought nearby, try to repel each other. This shows that like
charges repel while unlike charges attract each other.
2) Coulomb's
Inverse Square Law.
The law states
that the mechanical force, attraction or repulsion, between the two small
charged bodies is,
i) Directly
proportional to the product of the charges present on the bodies.
ii) Inversely
proportional to the square of the distance between the bodies and
iii) Depends
upon the nature of the medium surrounding the bodies.
The Fig 1. shows
two point charges, separates by distance 'd' meters. Te charges are Q1 and Q2
coulombs and K is the constant of proportionality.
According to
Coulomb's law, force between the charges can be mathematically expressed as
The constant
of proportionality, K depends on the surrounding medium and is given by,
Where ε0 = Absolute permittivity of the medium =
ε0εr
ε0 =
Permittivity of free space and εr =
Relative permittivity of the medium
For air, εr= 1
The concept of permittivity is discussed later.
Note : thus,
one coulomb of charge may be defined as that charge, which, wen placed in the
air or vacuum at a distance of one meter away from an equal and similar charge,
is repelled by a force of 9 x 10 N.
Read also
Electrostatic Field
Electric Flux
Electric Flux Density
Read also
Electrostatic Field
Electric Flux
Electric Flux Density