Unit of Electric Field

Overview

Coulomb's law deals with the force that acts between two distinct electric charges. According to the fundamental concept of the electric field,

● An electric charge modifies the space around it by producing an electric field.

● When another charge is introduced in this electrically modified region, it will experience some force due to the electric field produced by the first charge.

Coulomb's law is applied to static charges. An electric field is produced due to the motion of charged particles, and also when charges move relative to each other. Based on the experiments, it has been found that the electric field propagates through space at a finite speed (speed of light). The electric field concept is an essential aspect of the propagation of an electromagnetic wave through space, in a manner analogous to the propagation of light. By understanding the concept of the electric field, we can get to know how starlight travels vast distances through empty space.

Coulomb's law is based on the idea of force acting at a distance. This force is caused by an electric field and acts upon a charge placed in this electric field. The electric field is the real concept and is denoted by the electric field lines. The electric field lines are useful in describing the motion of a charge in the electric field.

Let us first try to understand the concept of the electric field of a static charge.

Definition of the electric field

The electric field \[\overrightarrow E \]is a vector quantity. It exists in almost every point of space. The electric field describes the force which acts on a particle that is placed in the field. 

For an arbitrary charged particle having charge q, the electric field is given by

\[\overrightarrow E  = \frac{{\overrightarrow F }}{q}\]

The dimension of the electric field is Newton's/coulomb or N/C.

Based on the electric field, the electric force is described as:

\[\overrightarrow F  = q\overrightarrow E \]

For a positive charge q, the direction of the electric field is in the same direction of the force vector.

We can calculate the value of the electric field by using Coulomb's law. By substituting a test charge q in the numerator of Columbus law, and a charge qi, we can get the electric field as follows.

Coulomb's Law: \[\overrightarrow F  = \frac{1}{{4\pi { \in _0}}}\frac{{q{q_i}}}{{{r^2}}}{\hat r_i}\]

 Electric field:  \[\overrightarrow E  = \frac{{\overrightarrow F }}{q} = \frac{1}{{4\pi { \in _0}}}\frac{{{q_i}}}{{{r^2}}}{\hat r_i}\]

Where \[{\hat r_i}\] is the unit vector, which indicates the direction of the electric field between from the source charge to the target test charge i.e., from q to qi.

Unit of Electric Field

The SI unit of an electric field is volt/meter.

Explanation: Electric field intensity is the force that acts on a unit positive charge placed in that field. The electric potential is the amount of work that is required to bring a positive unit charge from infinity to the point of influence of the electric field. From this explanation, we can say that, when a charged particle moves in a region of the electric field, an electric potential is developed. Thus, the electric potential is the work done in moving a particle. We can calculate the electric potential by multiplying the electric field with a displacement vector. Electric potential is given by:

\[E*r = v\]

Insights on electric field

The electric field is a modified electric force experienced by a unit positive test charge.

You can visualize the concept of the electric field in this way. Imagine a unit positive test charge placed at a point. Now bring a charge of higher magnitude near that test charge. The test charge will experience either a push or pull due to the influence of the electric field of the other charge. The force that the test charge experiences at any point of the electric field, when divided by the magnitude of the test charge, is the electric field at that point. The direction in which the test charge experiences force is the direction of the electric field at that point. An electric field exists even if the test charge is removed from that point.

FAQ (Frequently Asked Questions)

1. Calculate the value of an electric field?

Ans If you place a charged body in the presence of an electric field of another charged body, there will be some force acting on it. This phenomenon is best explained using Coulomb’s law.

Let us consider a charged object having charge Q1. A unit positive charge is placed at a distance r from the center of Q1. This field has the value:

So, Coulomb's law states that the force acting on the unit positive object is given by

Here it is considered that the medium in which both the objects are kept in either air or vacuum. The force experienced by unit test charge at a distance r, is the electric field of charge Q1 at that point. is the force vector that acts on the unit positive charge. is called the electric field strength for electric field intensity at a point.


2. What does an electric field look like?

We can visualize an electric field by drawing the electric lines of force which demonstrates the size, strength, and the area of influence of the electric field. These are called electric field lines. Electric field lines start from positive charges and end in negative charges. The direction of the electric field line at a point is the direction of force experienced by a unit positive charge placed at a point in the electric field. If the test charge is positive, the force experienced will be in the same direction of field lines, it is the test charge negative, the force experienced will be in the opposite direction of field lines.

Here is how the electric field lines of isolated positive and negative charge look like.

3. What is the direction of the electric field?

When you place a unit positive test charge in an electric field, under the influence of electrostatic force, the charge starts moving in the direction of the electric field. The charge either comes closer or moves farther from the source charge, depending upon the nature of the charge. The direction in which a unit positive charge moves shows the direction of the electric field. Hence the electric field is a vector quantity.