Electric charge and coulombs law

1. Electric Charge &
Coulomb’s Law
Dr Md Kaleem
Assistant Professor,
JIT, Jahangirabad, Darbhanga

2. Electrostatic
It is a branch of physics that deals with the
phenomena and properties of stationary or
slow-moving electric charges with no
acceleration.

3. Fundamental Law of Electrostatics
From various experimental evidences
following two laws were concluded known as
fundamental law of electrostatics
1. There are only two kinds of electric charges-
positive and negative
2. Like charges repel and unlike charges attract
each other

4. Conductors and Insulators
• The substances through which electric charges
can flow easily are called conductors while the
substances through which charges can not
flow easily are called insulators.

5. Electrostatic Induction
• It is the phenomenon of temporary
electrification of a conductor in which in
which opposite charges at its closer and
similar charges at its father end in the
presence of a nearby charged body.

6. Coulomb’s Law
• Coulomb’s Law:- It states that the electro-
static force of attraction or repulsion between
two charged bodies is directly proportional to
the product of their charges and varies
inversely as the square of the distance
between the two bodies.
F = Kq1q2/r2
Here, K = 1/4πε0 = 9×109 Nm2C-2 (in free space)

7. Relative Permittivity
Relative Permittivity (εr)
The relative permittivity (εr) of a medium is
defined as the ratio between its permittivity of
the medium (ε) and the permittivity (ε0) of the
free space.
εr = ε/ε0

8. Coulomb force in vector form
• Coulomb force in vector form:- The force on
charge q1 due to q2 is,
• S.I, q = ±1 Coulomb
• C.G.S, q = ±1 stat-coulomb
213
21
12 r
r
qq
kF



9. Dielectric Constant
• The dielectric constant (εr) of a medium can be
defined as the ratio of the force between two
charges separated by some distance apart in free
space to the force between the same two charges
separated by the same distance apart in that
medium.
So, εr = ε/ε0 = F1/F2
Here, F1 and F2 are the magnitudes of the force
between them in free space and in a medium
respectively.