Electric Charges and Fields Part -1
Electric Field
Charges are additive in nature.
q1
q2 q3
q1 q2 q3
Q=
Q
++
Like charges repel;Unlike charges attract
+



+
+
} Repel
Attract
+ve
-ve
Charges
COULOMB’S LAW
r
Fe = kq1q2
r2
F21= q1 q2
r2
21
1 4 Ꮛ0
q1 q2
k= 1
4 Ꮛ0
Ꮛ0 = permittivity of vaccum
=8.854 x 10-12C 2N-1m2
Vector form of Coulomb’s Law
r21 r21= r2-r1
F21= -F21
A region around a charged particle or object within which a force would be exerted on other charged particles or objects.
E=E 1 + E 2 +......+ E n
= kq 1 /r 1
2 + kq2 /r 2
2 +..... + kq n /rn
2
It is equal to the electric force per unit experienced by a test charge whi
The electric field intensity is the measure
strength of an electric field at any E= =
F q
E= k.Q
d2
= k.Q
d2
k . q. Q/d 2 q/
/
Newton / Coulomb
Electric Field Lines: Properties
Electric field lines start from a positive charge and end at a negative charge.
In case of a single charge, electric field lines end at infinity.
In a charge-free region, electric field lines are continuous and smooth.
Two electric field lines never intersect or cross each other.
Electric field lines never form a closed loop because electric field is conservative in nature.
+_
+_
Field lines
The electric field from an isolated positive charge
The electric field from an isolated negative charge
+
+
Cable jacket A leg insulator B leg insulator Conductors
Electrical Conductors Electrical Insulator
Conductors have free electrons on the surface which allows current to pass through. Insulators don’t.
Electric charge is quantized.
Q=n e
x
( NC-1)
The electric field intensity between two points is the vector sum of all the electric fields acting at that point.
Charge is a conserved quantity.
Net Charge q=0 (neutral)
gains 2 electrons loses 2 electrons
Steel Wood
Glass Rubber
Plastic Oil
Silver Gold
Sea
Water
Copper
CONDUCTOR
a
llows
the
energy
to
pass
through
it
INSULATOR
does
not
a
llows
the
energy
to
pass
through
it
of the point.
charge
ch is placed at that point