What Is The Kinetic Energy Of Light:Detailed Facts

Kinetic energy refers to the energy that causes anything to move. In this article, we’ll go through everything in depth concerning what is the kinetic energy of light. Herein we will explore and find out the answers to the list of following questions:

Image Credits: Image by Florian Kurz from Pixabay 

Energy is a property of items that can be transmitted to other objects or changed into various forms, but it cannot be generated or destroyed. It’s a quality of entities that may be transmitted to other objects or transformed into other kinds. Kinetic energy is the energy associated with moving things or movement.

Read more about energy basics and types

The following is the definition of kinetic energy:

“Kinetic energy of an object is the measure of the work an object can do by virtue of its motion.”

What is the kinetic energy of light
Kinetic Energy of Light

Measuring units of the kinetic energy:

The SI unit of kinetic energy is Joule i.e., equals 1 kg.m2.s-2

The CGS unit of kinetic energy is erg.

Read more about the uses of kinetic energy

Types of kinetic energy:

There are five types of kinetic energy as listed below

  • Radiant energy
  • Thermal energy
  • Sound energy
  • Electrical energy
  • Mechanical energy

Now, let us see what is the kinetic energy of light?

What is the kinetic energy of light?

Light energy is a kind of electromagnetic radiation with wavelengths that the human eye can perceive.

Kinetic energy is defined as energy that causes objects to move. If it has the ability to raise something, it is considered potential energy. However, it is the same energy that is presenting itself in different ways. Consequently, because the light is also only energy in motion, it may be referred to as “kinetic energy.”

Does light have kinetic energy?

When energy causes things to move, this is referred to as kinetic energy.

The light energy is a result of its motion. Because photons have no mass, their kinetic energy equals their total energy. So, the light has kinetic energy.

How to find kinetic energy of light?

Light, which is a kind of electromagnetic radiation, has kinetic energy.

The relativistic energy E of a particle od rest mass m0 and momentum p is given by

E2-p2c2 = m02c4

If the rest mass m0 of the particle is zero (such as for light also called as photons),

We have

E = pc  or p = E/c

But p = νE/c2

νE/c2= E/c

hence, ν=c

It shows that the speed ν of a particle of zero rest mass is always equal to c, the speed of light.

Also, we know that for a photon of frequency ν,


Where h = plank’s constant

Light is made up of particles with wave-like characteristics, such as photons. The idea of wave-particle duality is utilized to characterize this particular property of light that seems wave-like. The visible light wavelength ranges from 400 to 700 nanometres (nm).

Kinetic energy of light equation.

In order to calculate kinetic energy, multiply the mass by the square of the speed by the constant 1/2. This equation has two variables: the body’s mass (m) and its speed (v).

Its classical representation is as follow:


And its relativistic representation is given by,

How do you find kinetic energy at the speed of light?

If anything moves at the speed of light, it will have an infinite amount of kinetic energy, which is greater than the entire Universe. The reason behind this is that nothing can move faster or at a quicker rate than light.

According to classical mechanics, the kinetic energy of a body is determined by the mass of the body as well as the speed of the body.

The mass multiplied by the square of the speed, and multiplied by the constant 1/2, equals the kinetic energy. The following is the equation:



m = ​mass and v= speed (or the velocity) of the body

The following equation describes the relationship between an object’s classical kinetic energy and its momentum:


Where, P = momentum

To compute the kinetic energy of a body whose speed is a large fraction of that of light, one must use special relativity to account for the fact that the body is moving to the speed of light. It is important to comprehend how to use special relativity to problems involving high-speed particles in order to solve them.

To account for linear momentum in special relativity, we must modify the formula. The relativistic formulation for linear momentum utilizes m for rest mass, v, and v for velocity and speed, respectively, and c for the speed of light in vacuum, the relativistic expression for linear momentum is:


Where γ= Lorentz factor

Considering that an object’s kinetic energy is proportional to its momentum, we naturally see that the relativistic formula for kinetic energy would differ from its classical equivalent. As a matter of fact, the relativistic formulation for kinetic energy is as follows:

The equation demonstrates that the energy of an object approaches infinity when the object’s velocity v approaches the speed of light c . The conclusion is that an item cannot be accelerated past this boundary.

How do you find kinetic energy from momentum?

Kinetic energy is the quantity of energy that any material has as it accelerates, whereas momentum is the amount of mass that an item has when it is moving.

Multiply and divide R.H.S. by m

We know that p=mv. Substituting for mv in the above equation we get,

How are kinetic energy and momentum related?

There exists a correlation between kinetic energy and momentum because of their connections with mass and velocity

Using mathematics, the relationship between kinetic energy and momentum may be expressed as

As a result, we may state that a body’s kinetic energy is the relationship between a substance’s linear momentum and its kinetic energy that is being studied.

Because of the energy momentum relation, momentum increases directly with speed in a constant object, but Kinetic energy grows in direct proportion to the square of the velocity.

So, here in this article, we have studied what is the kinetic energy of light.

Prajakta Gharat

I am Prajakta Gharat. I have completed Post Graduation in physics in 2020. Currently I am working as a Subject Matter Expert in Physics for Lambdageeks. I try to explain Physics subject easily understandable in simple way.

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