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# 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:

- E.M waves are formed by accelerated ionized particles.
- No medium is required for the propagation of E.M waves.
- The velocity of E.M waves = velocity of light
- In free space velocity of E.M waves ⇒C=1/√𝜇0𝝐0
- In any other medium velocity of E.M waves ⇒v=1/√𝜇𝝐
- E.M waves follow the principle of superposition.
- In free space relation between E and B is, c=E/B
- 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-

- Gauss law for static electricity
- Gauss law for magnetism
- Faraday’s law for electromagnetic induction and
- Maxwell-Ampere rotation law

Now the equations are-

- ∫E.ds=q/𝝐
_{0}{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. - ∫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.
- ∫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.
- ∫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,

- If light propagating in x-direction it can be written as E=E
_{0}(𝜔t-x/c) &B=B_{0}(𝜔t-x/c) { B_{0}=amplitude of magnetic field, E_{0}= amplitude of electric field,*𝜔*= angular frequency} - 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 - The energy density of electromagnetic field: u= 𝝐
_{0}E^{2}/2 + B^{2}/2𝜇_{0} - Average energy density = 𝝐
_{0}E^{2}/2 = B^{2}/2𝜇_{0}

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

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