Electric Field

Student with basic knowledge of electrostatics must have studied about electric field in many books with no proper definition in most of the books. But what exactly is electric field which is only said to be existed in any region in which electric force is said to be existed and this question is not the easiest one to answer. It was Michael Faraday who first referred to an electric ‘‘field of force,’’ and James Clerk Maxwell identified that field as the space around an electrified object – a space in which electric forces act. We all know that electric field and force are closely related and most basic definition of electric field is the electric force per unit area acting on the charged object.
E=F(r)/q
where this charge q is often known as test charge.
Since electric field in general is altered by the presence of test charge
E = lim Δq 0 ΔF Δq = dF dq
So, it is clear from above discussion that 

(1) E is a vector quantity with magnitude directly proportional to force and with direction given by the direction of the force on a positive test charge.
(2) E has units of newtons per coulomb (N/C)
While applying Gauss's law it is helpful to visualize electric field near charged object and the most common
approach is  to construct a visual representation of an electric field which is to use a either arrows or ‘‘field lines’' that point in the direction of the field at each point in space as shown below



  • So, electric field line is an imaginary line drawn in such a way that it's direction at any point is same as the direction of field at that point.
  • An electric field line is, in general a curve drawn in such a way that the tangent to it ateach point is the direction of net field at that point.
  • Field lines of a single position charge points radially outwards while that of a negative charge are radially inwards as shown below in the figure.

  • Field lines around the system of two positive charges gives a different picture and describe the mutual repulsion between them.

  • Field lines around a system of a positive and negative charge clearly shows the mutual attraction between them as shown below in the figure.

  • Some important general properties of field lines are
    1.Field lines start from positive charge and end on a negative charge.
    2.Field lines never cross each other if they do so then at the point of intersection there will be two direction of electric field.
    3.Electric field lines do not pass through a conductor , this shows that electric field inside a conductor is always zero.
    4.Electric field lines are continuous curves in a charge free region.

  • I would like to say that you can think of electric field as a quantity filling the space in the neighborhood of an electric charge. The electric-field concept helps us understand not only the forces between isolated stationary charged bodies but also what happens when charges move. When charges move, their motion is communicated to neighboring charged bodies in the form of a field disturbance.

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