Electric field
Electric field of a given charge is the space around the
charge where electrostatic coulomb’s force of attraction or repulsion can be
experienced by a second charge or by a foreign charge.
[be remember to measure the strength of any electric field
always a unit positive charge is used]
Electric field intensity
At a particular position in space the electric field
intensity is defined as the electrostatic force experienced by a unit positive
charge at that position.
Suppose P is a source
point charge and +q is a positive charge at a distance r, and it’s position vector from the charge P is
denoted as 
Now from coulomb’s law the electrostatic force (F) acting on +q is
Then the electric field intensity denoted as E at that position for +q charge is
∴ the SI unit of electric field intensity is
Point to be noted:
1)What will happen if +q =
1C positive charge, then
or E = F
That means electric field intensity is equal to the
electrostatic force. This creates the definition of electric field intensity.
Electric field intensity at a particular position in space is
define as the electrostatic force experienced by a unit positive charge at that
position.
2)To test electric field intensity always a positive charge
is used (+q is positive)
3) Electric field intensity at a particular position from the
source charge is always constant, it is independent from the amount of test
charge +q. it is only depend only on amount of
source charge P
4) Since electric field intensity is constant at a particular
distance from the source charge. Hence electric field intensity is spherically
constant from the original source charge.
5) For a positive source charge electric field is radially
outward--->
For a negative charge electric field is radially
inward---->
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