Download Electric Field Important Point Electric Displacement Vector

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Electricity
Electric Field
When a charge is placed near to another charge, it experiences an electrostatic force
according to coulomb's law. The space around any charge upto which any other charge experiences
a force, is called electric field or electrostatic field due to that charge.

F

N/C
E = q
Mathematically
...(1)
If charge q1 is placed near to charge q2 then electric field due to q1 is
1 q1 q 2 1

E = 4 0 r 2 q 2
1 q1 N

r̂
=
E
40 r 2 C
...(2)

Electric field intensity E or the strength of an electric field at a given point is the force
 
exerted or a unit +ve charge placed at that point.
Here it can be summed up that the electrostatic force experienced by a charge q2 in an

electric field E is


...(3)
F = q2 E N
Important Point
(comparison of electrostatic forces with Gravitational force)
1.
Electrostatic force can be attractive or repulsive but gravitational force can only be
attractive in nature.
2.
Charges can be +ve or –ve but mass is always +ve in nature.
3.
Coulombs law of electrostatic fine is also a inverse square low similar to Newton's
law at Gravitation.
Electric Displacement Vector

The electric displacement vector D at any point in a isotropic any linear medium having
 

electrical permittivity  m is related with electric fixed intants E is given by
 
Electricity
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

D = m E
In free space


D0 =  0 E
SI unit of electric displacement is C/m2.
Superposition principle
According to this principle when more then one charges interact with unit positive charge,
then the net intensity on the text charge is the vector sum of the intensity due to individual charge.




i.e.
E = E1  E 2  ...  E n