CHAPTER (2)
Electric Charges, Electric Charge
Densities and
Electric Field Intensity
,Charge Configuration
a) Point Charge:
The concept of the point charge is used when the
dimensions of an electric charge distribution are very
small compared to the distance to the neighboring
charges, i.e. the point charge is occupying a very small
physical space
b) Distributed Charge
The charge may be distributed along a line, among a
surface or among a volume.
(1) Line Charge: +
++ ++
+
+
+
The line charge density 𝝆𝒍 is dl
+
+
dQ = ρL dl
defined as the charge per unit +
+
+ + + +
length.
∆𝑸 𝑪
𝝆𝒍 = 𝒍𝒊𝒎∆𝒍→𝟎 � �𝒎�
∆𝒍
𝒅𝑸
𝝆𝒍 = �𝑪�𝒎�
𝒅𝒍
So,
𝒅𝑸 = 𝝆𝒍 𝒅𝒍
The total charge Q of the line can be determined by
, 𝒍 𝒍
𝑸 = � 𝒅𝑸 = � 𝝆𝒍 𝒅𝒍 [𝑪]
𝟎 𝟎
For uniform line charge, where 𝝆𝒍 is constant
𝑸 = 𝝆𝒍 𝒍 [𝑪]
(2) Surface Charge:
U
The surface charge density 𝝆𝒔 is defined as the charge
per unit surface area.
∆𝑸
𝝆𝒔 = 𝒍𝒊𝒎∆𝒔→𝟎 �𝑪� 𝟐 �
∆𝒔 𝒎
𝒅𝑸
𝝆𝒔 = �𝑪� 𝟐 �
𝒅𝒔 𝒎
So,
𝒅𝑸 = 𝝆𝒔 𝒅𝒔
The total charge Q of the surface can be determined by
Electric Charges, Electric Charge
Densities and
Electric Field Intensity
,Charge Configuration
a) Point Charge:
The concept of the point charge is used when the
dimensions of an electric charge distribution are very
small compared to the distance to the neighboring
charges, i.e. the point charge is occupying a very small
physical space
b) Distributed Charge
The charge may be distributed along a line, among a
surface or among a volume.
(1) Line Charge: +
++ ++
+
+
+
The line charge density 𝝆𝒍 is dl
+
+
dQ = ρL dl
defined as the charge per unit +
+
+ + + +
length.
∆𝑸 𝑪
𝝆𝒍 = 𝒍𝒊𝒎∆𝒍→𝟎 � �𝒎�
∆𝒍
𝒅𝑸
𝝆𝒍 = �𝑪�𝒎�
𝒅𝒍
So,
𝒅𝑸 = 𝝆𝒍 𝒅𝒍
The total charge Q of the line can be determined by
, 𝒍 𝒍
𝑸 = � 𝒅𝑸 = � 𝝆𝒍 𝒅𝒍 [𝑪]
𝟎 𝟎
For uniform line charge, where 𝝆𝒍 is constant
𝑸 = 𝝆𝒍 𝒍 [𝑪]
(2) Surface Charge:
U
The surface charge density 𝝆𝒔 is defined as the charge
per unit surface area.
∆𝑸
𝝆𝒔 = 𝒍𝒊𝒎∆𝒔→𝟎 �𝑪� 𝟐 �
∆𝒔 𝒎
𝒅𝑸
𝝆𝒔 = �𝑪� 𝟐 �
𝒅𝒔 𝒎
So,
𝒅𝑸 = 𝝆𝒔 𝒅𝒔
The total charge Q of the surface can be determined by
