# Everything You Need To Know About Electromagnetic Waves

Before we start our today’s topic let’s talk about the topic first. I mean-

## What are E.M waves?

If there exists a variable electric field and magnetic field in any place, then it spreads around like a wave called Electromagnetic Wave.

## Properties of E.M waves:

1. E.M waves are formed by accelerated ionized particles.
2. No medium is required for the propagation of E.M waves.
3. The velocity of E.M waves = velocity of light
4. In free space velocity of E.M waves ⇒C=1/√𝜇0𝝐0
5. In any other medium velocity of E.M waves ⇒v=1/√𝜇𝝐
6. E.M waves follow the principle of superposition.
7. In free space relation between E and B is, c=E/B
8. When E.M waves propagate they carry energy with them. This energy is equally divided into an electric field and a magnetic field.

Scientist Maxwell expresses the four basic laws of electricity and magnetism with the help of four equations. The laws are-

1. Gauss law for static electricity
2. Gauss law for magnetism
3. Faraday’s law for electromagnetic induction and
4. Maxwell-Ampere rotation law

Now the equations are-

1. ∫E.ds=q/𝝐0 {E & ds are vector quantity}. It is independent of time and equally applicable for static and dynamic charges. From this equation, it comes to know that the electric force line is not a closed curve.
2. ∫B.ds=0 {B & ds are vector quantity}.It is also independent of time. From this equation, it comes to know that the existence of a single magnetic pole is not possible and the magnetic force line is a closed curve.
3. ∫E.dl= -d/dt(∫B.ds) . It depends on time. According to this equation, the path integration of the electric field in a closed path is equal to the change in electric flux in that path.
4. ∫B.dl=𝜇0{I+𝜺0(d𝜑E/dt)} .{𝜺0(d𝜑E/dt)=iD(displacement current)} It is also depend on time. From this equation, we can conclude that changing the electric fields can produce a magnetic field.

Now it’s time to some important points,

1. If light propagating in x-direction it can be written as E=E0(𝜔t-x/c) &B=B0(𝜔t-x/c) { B0 =amplitude of magnetic field, E0 = amplitude of electric field, 𝜔 = angular frequency}
2. Radiation pressure: It is exerted upon any surface due to the exchange of momentum between the object and the electromagnetic field. Radiation pressure, p=(2I/c)r+ (I/c)(1-r) {r=reflection coefficient}
p=I/c ; for complete absorption
p=2I/c ; for complete reflection
3. The energy density of electromagnetic field: u= 𝝐0E2/2 + B2/2𝜇0
4. Average energy density = 𝝐0E2/2 = B2/2𝜇0

These are the basic things you have to know in this chapter.

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