# Formula of Electric Field Intensity – Definition, Units

In an article on properties of electric charge, we have learned that an electric charge produces electric field and magnetic field around it. Basically, an electric charge can move due to electrostatic force and this force comes from the electric field. Now, what is an electric field and the intensity of electric field? What is the formula for electric field intensity? In this article, we are going to explain the concept of electric field & electric field intensity and the formula for electric field intensity.

Contents in the article:

• Electric Field
• Definition of Electric Field
• Formula of Electric Field Intensity
• Force on a charge placed in external electric field
• Unit of Electric Field Intensity
• Dimension of Electric Field Intensity

## What isElectric Field?

Electric Field is the region around a charge inside which this charge interacts with other charges. If the electric field is due to a positive charge then it will attract other positive charges and repels other negative charges within this region. This region is a spherical region for a point charge. But, it may not be spherical for other charge distributions. The charge that creates the electric field is known as the source charge and the charges that experience electric force in that region are the test charges.

## Intensity of Electric Field

Electric Field and electric field intensity are not the same thing. Then, what is electric field intensity?

Electric field Intensity at a point is the strength of electric field at that point inside the electric field region. Electric field Intensity at a point inside the electric field is defined as the electric force on an one coulomb positive charge placed at that point. So, it is nothing but the electric force per unit positive charge. It is denoted by the letter E. Some authors write electric field intensity as the Electric field. But these two terms are conceptually different.

If a positive charge +Q produces an electric field E around it, then the electric force on a positive q charge in this electric field region is F = qE. Electric field Intensity (E) is a vector quantity that has the same direction as that of the electric force.

## Electric Field Intensity formula

One can determine the expression or formula for electric field intensity directly from the Coulomb’s Law or by applying Gauss’s law of electrostatics.

The strength of intensity of electric field (E) at r distance produced by a positive charge Q is, $\color{Blue} E = K \frac{Q}{r^2}$………(1)

This is the formula for electric field intensity. Sometimes, it is also called the electric field formula.

where K is coulomb’s constant.

In SI system, k = 9×109 and in CGS system, K =1.

Again, the relation between electric field and electric force is F=qE.

## Units of electric field intensity

One can find the unit of electric field intensity from the equation, F=qE or, E=F/q

We know that the SI unit of force is Newton (N) and the SI unit of charge is Coulomb (C).

So, SI unit of electric field Intensity is N/C. It has another SI unit as Volt/metre (V/m).

CGS unit of electric field Intensity is dyn/statC or dyn/esu.

## Dimension of the intensity of electric field

Dimension of force is [ MLT-2 ] and the dimension of electric charge is [ TI ]. Now, the dimension of electric field intensity is equal to the dimension of electric force divided by the dimension of electric charge.

So, the dimensional formula of electric field intensity is [ MLT-3I-1 ].

## Difference between electric field and electric field intensity

The electric field is the region around a charge inside which it can interact with other charges. But the intensity of electric field at a point gives the strength of the electric field at that point. Electric field intensity is actually the electric force on a unit positive charge placed inside the electric field. In higher classes, the term electric field itself represents the electric field intensity. Because, there is no applications of the region around the charge. But the strength of that region is important.

## Numerical problems on electric field

1. What will be the electric field at a point at 10 cm distance from a +5 C charge? If we place another +2 C charge at that point, what will be the electrostatic force on +2 C charge?

Hints: Use equation-(1) to find electric field and use Coulomb’s law to find electrostatic force.

This is all from this article on the definition, unit and formula of electric field and the intensity of electric field. If you have any doubt on this topic you can ask me in the comment section. You also can visit my website to see other posts related to Electronics and Physics.

Thank you!

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