Electric Field Intensity

The electric field intensity is defined as the amount of force which a unit charge experiences when placed in an electric field. It is a vector quantity as its value is defined by magnitude along with the direction.

It is the measure of the force which is exerted by the source charge on the test charge present in the electric field of the source charge.


The symbolic representation used for electric field intensity is E.

Electric field intensity is sometimes also known as electric field strength.

What is an Electric Charge?

The fundamental quantity responsible for the generation of electricity is known as electric charge.

We know that the smallest particle from which all materials are composed is an atom. However, there are three sub-atomic particles of an atom, namely, electron, proton and neutron. Electron and Proton are referred to as charged particles. The electrons are negatively charged particles, while protons possess positive charge and neutrons are neutral.

The charge is regarded as the fundamental property of atom due to which the nearby objects experience either attractive or repulsive forces.

The two types of charges are:

  • Positive and
  • Negative

The amount of charge possessed by a material is measured in Coulombs.

This property of charge is the reason why bodies present in the electric field experiences a certain force.

Before proceeding the discussion further with electric field intensity. See,

What is an Electric Field?

You all may have read the definition of the electric field many times before coming across this article. Let us understand the term electric field here in the simplest possible way.

Suppose we have an electric charge present at a point in space, and definitely its presence will have some effect on its surrounding region. So, the space or region up to which the effect of that particular charge exists is known as its Electric Field.electric field of charge Q This effect is nothing but a force which the charge exerts to the other charge which is present in the region around it.

It is noteworthy here that the electric field produced due to the presence of a stationary charge in space is time-invariant in nature. Thus, known as the static electric field.

What is Electric Field Intensity?

We have already discussed in the beginning that electric field intensity is defined as the amount of force a unit charge experiences when present in an electric field.

More simply, it is said in a way that, the strength of the electric field which is generated by the charge is determined by another charge placed in its nearby region. This charge is referred to as a test charge. While the charge which acts as the source of the electric field is known as source charge.

Both magnitude, as well as direction, is associated with electric field intensity. This is so because when the source charge is of positive polarity then the strength of the electric field is necessarily directed away from the test charge (of the same polarity). As against, when the source charge is negative then the field intensity is directed in the direction towards the test charge (with opposite polarity).

This is the reason this quantity is a vector in nature.


Suppose a charge Q is present in vacuum at a certain point. If we place another charge say q in the region near it, then the charge Q will apply some force say F to the charge q.electric field intensity

The reason behind this is that there exists a field near the region where Q is placed. So, when another charge is placed in this field then it acts on the charge and this results in force.

According to Coulomb’s Law, the force experienced by q when present in the field generated by Q is given as:electric field intensity eq1

Further, the force per unit charge will be,electric field intensity eq2

Thus, the amount of force exerted per unit of charge is the electric field intensity or electric field strength. It is denoted by E.electric field intensity eq3

It is to be noted here that as q is also a charged particle thus it will also have its electric field and so it will also apply a certain amount of force on Q. This is the reason, q i.e., test charge is considered negligibly small.

Unit of Electric Field Intensity

Basically, magnitude wise the electric field is the force exerted per unit charge. Thus, given as,electric field intensity eq4 As force is measured in newtons while the unit of charge is the coulomb. Thus, the unit for electric field intensity is Newton per Coulomb (N/C).

Also, we know, the electric potential is given as:

V= J/C = Nm/C

Thus, Volt/metre (V/m) is another unit used for measuring the electric field intensity.

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