ELECTRIC FIELD (COULOMBS LAW)-When two charges are placed at a distance apart , they exert force on each other. Such a force is called action at a distance .
Coulomb ‘s law in electrostatic provides a method to find the magnitude of force between two point charges kept at a distance . It can not explain the mechanism as to how two charges exert force on each other at a distance . The concept of electric field provides an explanation as to how a charge can exert force on another charge kept at a distance from it . According to field concept , the force between two charges is a two- step process .
In order to explain , consider that a charge q is present at some point in space . In the first step , it is assumed that the charge q creates something, called electric field in the space around it . Likewise, charge q creates something, called electric field in the space around it . Likewise charge q is called source charge. In the second step , it is assumed that when another charge qº , called test charge, is placed in the electric field produced by the source charge q, the electric field exerts force on it.
Thus , electric field due to a charge is the space around the charge, in which any other charge is acted upon by an electrostatic force.
The electric field of a charge is the space property by virtue of which the charge modifies the space around itself.As a result,if any other charge is brought in the space around the charge,it experiences electrostatic force.It may be pointed out that the source charge does not experience any force due to electric field produced by it. The electric field due to a source charge has its own existence and is present even if there is no test charge to experience the force. The significance of electric field lies in the fact that the space around the charge is important rather than the charge that produces it.Further, the electric field takes finite time to propagate.If a charge is displaced from its position, the change in electric field at a distance r will be noticed after a time r/C,where C is the speed of light.
ELECTRIC FIELD (COULOMBS LAW)
The electric field intensity at a point due to a source charge may be defined as the force experienced per unit positive test charge placed at that point without disturbing the source charge. The electric field intensity is also called strength of electric or simply electric field .
Consider that a positive test charge qº experiences a force F , when placed at the observation point ( the point , where electric field is to be determined) . Then electric field at the observation point is given by
Ē = F/qº
In the above expression for electric field it is assumed that when the test charge qº is placed at the observation point , it does not disturb the source charge. One way to ensure that the test charge qº does not disturb the source charge is to keep its magnitude vanishingly small . If the test charge qº is not vanishingly small, it will disturb the source charge and hence electric field at the observation point will be different from the one , had the source charge remained in its original position.
Therefore electric field intensity at a point due to a source charge may be defined as the force experienced per unit positive charge on a vanishingly small positive test charge placed at that point.
If F is the force experienced by positive test charge qº placed at the observation point ,then electric field at that point is given by
Ē = Lt (qº→0) F/qº
The idea of taking the limit qº→0 is that on placing the test charge at the observation point, the source charge will not be disturbed.
The electric field at a point is a vector quantity.From equation (2.01) or (2.02),it follows that unit of electric field in SI is Newton /colomb (N/ C).
Force on a charge inside electric field. If vector E is electric field at a point , then by definition , a charge q placed at that point will experience a force Vector F given by
F= qE ( F and E are vectors ) .
PHYSICAL SIGNIFICANCE OF ELECTRIC FIELD:
THE concept of electric field is of a great significance . Two charges kept at a distance exert force on each other, which is termed as action at a distance. The concept of electric field helps us to understand the mechanism by which two charges kept at a distance exert force on each other.Further,find the force experienced by one charge due to the other in terms of the electric field produced by it.
ELECTRIC FIELD (COULOMBS LAW)
ELECTRIC FIELD(COULOMBS LAW)