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Name : 1) Abhishek Yadav 130360111001
2) Prakash Giri 130360111002
3) Kheni Niral 130360111003
4) Bhadresh Langadiya 130360111004
Branch : Electronics & Communication
Faculty :
1) V.S.Kansara
a)
form
F  kq1q2 /r
2
b) Units
Two possibilities:
- define k and derive q (esu)
- define q and derive k (SI) √
9 10 N  k(1C) /(1m)
9
2
 k  9  10 N
9
2

For practical reasons, the coulomb is defined using
current and magnetism giving
k = 8.988 x 109 Nm2/C2

Permittivity of free space
0 
Then
F 
1
 8.84 10 12 C 2 / Nm2
4k
1
40
c) Fundamental unit of charge

e = 1.602 x 10-19 C
q1q2
r2
Net force is the vector sum of forces
from each charge
F3
q1
q2
q
q3
F2
F1
Net force on q:
F = F1 + F2 + F3
F
- abstraction
- separates cause and effect in Coulomb’s law
a) Definition
r
r
F
E 
q0

Units: N/C
b) Field due to a point charge
q0
F
Q
r
Coulomb’s law:
Electric Field:
r r
E // 
F
Qq0
Fk 2
r
Q
E  F /q0  k 2
r
direction is radial
Net field is the vector sum of fields from each
charge
E3
q1
q2
P
q3
E2
E1
Net field at P: E = E1 + E2 + E3
E
a) Direction of force on positive charge
radial for point charges
out for positive (begin)
in for negative (end)
b) Number of lines proportional to charge
Q
2Q
d) Line density proportional to field strength
Line density at radius r:
N
1

2  2
4r
r
Number of lines
area of sphere


Lines of force model <==> inverse-square law
a) dipole
b) two positive charges
c) Unequal charges
d) Infinite plane of charge
+
+
+ +
+
+ +
+
+ +
+ q,
+
E
A
By comparison with the
field from a point charge,
we find:
Field is uniform and constant to ∞,
in both directions
Electric field is proportional to the line
density, and therefore to the charge
density, =q/A

E
2 0
e) Parallel plate capacitor
compared to the size)
E+
E-
EL=0
+
+
+
+
E+
E-
E=2E+
-
+
-
+
-
• Strong uniform field between:
• Field zero outside
(assume separation small
E+
E-
ER=0
E   /0
f) Spherically symmetric charge distribution
• Symmetry ==> radial
• number of lines prop. to charge
+
+
+
+
+
+
+
+
Outside the sphere:
r kq
E  2 rˆ
r
as though all charge concentrated at the
centre (like gravity)