Electromagnetic Waves

What are Electromagnetic Waves?

Electromagnetic waves are also known as EM waves. Electromagnetic radiations are composed of electromagnetic waves that are produced when an electric field comes in contact with the magnetic field. It can also be said that electromagnetic waves are the composition of oscillating electric and magnetic fields. Electromagnetic waves are solutions of Maxwell’s equations, which are the fundamental equations of electrodynamics.

How are Electromagnetic waves formed?

• Generally, an electric field is produced by a charged particle. A force is exerted by this electric field on other charged particles. Positive charges accelerate in the direction of the field and negative charges accelerate in a direction opposite to the direction of the field.
• The Magnetic field is produced by a moving charged particle. A force is exerted by this magnetic field on other moving particles. The force on these charges is always perpendicular to the direction of their velocity and therefore only changes the direction of the velocity, not the speed.
• So, the electromagnetic field is produced by an accelerating charged particle. Electromagnetic waves are nothing but electric and magnetic fields travelling through free space with the speed of light c. An accelerating charged particle is when the charged particle oscillates about an equilibrium position. If the frequency of oscillation of the charged particle is f, then it produces an electromagnetic wave with frequency f. The wavelength λ of this wave is given by λ = c/f.  Electromagnetic waves transfer energy through space.

Electromagnetic waves are shown by a sinusoidal graph. It consists of time-varying electric and magnetic fields which are perpendicular to each other and are also perpendicular to the direction of propagation of waves. Electromagnetic waves are transverse in nature. The highest point of the wave is known as crest while the lowest point is known as a trough. In vacuum, the waves travel at a constant velocity of 3 x 108 m.s-1.

Mathematical Representation of Electromagnetic Wave

A plane Electromagnetic wave travelling in the x-direction is of the form

$E(x,t)=E_{max}\cos (kx-\omega t+\Phi )$

$B(x,t)=B_{max}\cos (kx-\omega t+\Phi )$

Speed of Electromagnetic Waves in Free Space

It is given by 

$C=\frac{1}{\sqrt{\left({\mu }_0{ϵ}_0\right)}}$

Where,

${\mu }_0$ is called absolute permeability. It’s value is $1.257\times {10}^{-6}Tm{A}^{-1}$

${ϵ}_0$ is called absolute permittivity. It’s value is $8.854\times {10}^{-12}{C}^2{N}^{-1}{m}^{-2}$

C is the velocity of light in vacuum = velocity of electromagnetic waves in free space = $3\times {10}^{8}m{s}^{-1}$

Electromagnetic Spectrum

Electromagnetic waves are classified according to their frequency f or according to their wavelength $\lambda =\frac{c}{f}$.

Wavelength ranges of different lights are as follows,

For visible light – approx. 400 nm to approx. 700 nm

For violet light – approx. 400 nm

For red light – approx. 700 nm

Applications of Electromagnetic Waves

Following are a few applications of electromagnetic waves:

• Electromagnetic radiations can transmit energy in vacuum or using no medium at all.
• Electromagnetic waves play an important role in communication technology.
• Electromagnetic waves are used in RADARS.
• UV rays are used to detect forged bank notes. Real bank notes don’t turn fluorescent under the UV light.
• Infrared radiation is used for night vision and is used in security camera.