Electric charge

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.

  1. There are two types of electric charges: positive and negative.
  2. Charge is a scalar quantity.
  3. SI unit of charge is Coulomb (C) and is generally denoted by q.
  4. Like charges repel and unlike charges attract each other.
  5. 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.
  6. Value of fundamental or basic unit of charge is (e = 1.6 x 10-19 C).
  7. An infinitesimally small positive charge experiencing electric force is called a test charge. A unit positive charge is commonly used as a test charge.
  8. 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
  • Charge cannot exist like ±e/2,±e/3,….
  • Millikan’s oil-drop experiment proves the existence of charges as integral multiple of basic charge e.
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.

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