Question

Discuss various aspects of the electric field.

Answer 1

1. If the charge q is positive then the electric field points away from the source charge and if q is negative, the electric field points towards the source charge q. This is shown in the following figure.
   
   
   Electric field of positive and negative charges
2. If the electric field at a point P is `vec"E"`, then the force experienced by the test charge q₀ placed at the point P is `vec"F" = "q"_0 vec"E"`. This is Coulomb’s law in terms of electric field. This is shown below in Figure.
   
   
   Coulomb’s law in terms of electric field
3. The equation implies that the electric field is independent of the test charge q₀ and it depends only on the source charge q.
4. Since the electric field is a vector quantity, at every point in space, this field has a unique direction and magnitude as shown in the following figures (a) and (b). From equation, we can infer that as distance increases, the electric field decreases in magnitude. Note that in below figures (a) and (b) the length of the electric field vector is shown for three different points. The strength or magnitude of the electric field at point P is stronger than at the point Q and R because point P is closer to the source charge.
   (a) Electric field due to positive charge-
   
   (b) Electric field due to negative charge-
   
5. In the definition of the electric field, it is assumed that the test charge q₀ is taken sufficiently small, so that bringing this test charge will not move the source charge. In other words, the test charge is made sufficiently small such that it will not modify the electric field of the source charge.
6. The expression is valid only for point charges. For continuous and finite-size charge distributions, integration techniques must be used. However, this expression can be used as an approximation for a finite-sized charge if the test point is very far away from the finite-sized source charge.
7. There are two kinds of electric field: uniform (constant) electric field and non-uniform electric field. Uniform electric field will have the same direction and constant magnitude at all points in space. A non-uniform electric field will have different directions or different magnitudes or both at different points in space. The electric field created by a point charge is basically a non-uniform electric field. This non-uniformity arises, both in direction and magnitude, with the direction being radially outward (or inward) and the magnitude changes as distance increases.
   
   
   
   
   Uniform and non-uniform electric field