Electric charge
Electrostatics is a branch of physics that deals with the phenomena and properties of stationary or slow-moving electric charges with no acceleration.
Electric charge is the physical property of matter that causes it to experience a force when placed in an electromagnetic field.
- There are two types of electric charges: positive and negative.
- Charge is a scalar quantity.
- SI unit of charge is Coulomb (C) and is generally denoted by q.
- Like charges repel and unlike charges attract each other.
- When a body gets the static charge by any means then body is said to be electrified or charged. When it has no charge it is said to be neutral.
- Value of fundamental or basic unit of charge is (e = 1.6 x 10-19 C).
- An infinitesimally small positive charge experiencing electric force is called a test charge. A unit positive charge is commonly used as a test charge.
- If the sizes of charged bodies are very small as compared to the distances between them, we treat them as point charges.
Basic Properties of Charge
|
1.
|
Quantization of Electric charge
|
Quantization is the property of an electric charge which tells that any charged body can have charge which is an integral multiple of the basic charge ‘e’.
q = ±ne
q= total charge
n = 1,2,3,4….
e = charge on electron i.e. 1.6 × 10–19 C
|
|
2.
|
Additivity of Electric charge
|
Electric charge is additive.Total charge on an extended body is the algebraic sum of charges in different regions of the body.
|
|
3.
|
Invariance of Electric Charge
|
Electric charge is independent of frame of reference i.e. charge on a body does not vary whatever may be its speed or the speed of the observer i.e.Charge at rest = Charge at motion
|
|
4.
|
Conservation of Electric Charge
|
Charge can neither be created nor destroyed in an isolated system.
|
Comparison of Electric Charge and Mass
|
S.No.
|
Electric Charge
|
Mass
|
|
1.
|
Electric charge may be positive or negative quantity.
|
Mass of a body is always a positive.
|
|
2.
|
Charges can be added like real numbers so they can be treated as scalars.
|
Masses can also be added like real numbers and are scalars.
|
|
3.
|
Charge is quantized.
|
Mass of a body is not considered to be quantized.
|
|
4.
|
Charge is always conserved.
|
Mass is not conserved as mass can be changed into energy and vice-versa according to the relation E = mc2
|
|
5.
|
Charge on a body is not affected by the velocity of the body i.e. charge is invariant.
q(at rest) = q(in motion)
|
Mass of a body changes with velocity of the body.
|
|
6.
|
Force between charges may be attractive
(in case of unlike charges) or repulsive
(in case of like charges).
|
Force between masses is always attractive.
|
|
7.
|
It plays an important role in electricity.
|
It has an important role in gravitation.
|
|
8.
|
In SI, charge is a derived physical quantity.
|
In S.I., mass is a fundamental physical quantity.
|
|
9.
|
Charge may not exist without mass.
|
Mass exists without net charge also.
|