Electromagnetic Waves

Hello friends, today this post is about electromagnetic waves.

We all have heard about electromagnetic waves but most of us can’t draw a clear picture of Electromagnetic waves. Today we will try to understand this intuitively. It may or may not be exact but surely help you to develop better intuition.

What is Electromagnetic Waves?

Simply we can say electromagnetic wave is a current. Yes, it is a current. Not the conduction current but displacement current.

What are the properties of current at higher frequency?

• It can radiate into space as electromagnetic waves (radio waves). This is the basis of radio technology.
•  It does not penetrate deeply into electrical conductors but tends to flow along their surfaces; this is known as the skin effect.
•  Currents applied to the body often do not cause a painful sensation and muscular contraction of electric shock that lower frequency currents produce
• Current can easily ionize the air, creating a conductive path through it.
• Another property is the ability to appear to flow through paths that contain insulating material, like the dielectric insulator of a capacitor.

Generally, the current that reaches our house is at 50 Hz /60 Hz but electromagnetic wave has a frequency in range of Kilo Hertz, Megahertz, and Gigahertz. That’s why they can travel in space.

Here is a list of medium we use for the different frequencies of current.

• Lower frequency: metal wire, power cables
• Radio frequency: Transmission lines
• Microwave frequency: Wave guides
• Visible range: Optical cables

 

Now, we will talk about how they propagate?

They propagate with help of antenna. An antenna is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver.

Two basics principles are that:

•     Changing the magnetic field causes generation of electric filed.
•     Changing the electric field causes generation of magnetic field.

Basic property of charge:

•     Charge at rest creates an electric field.
•      Charge in motion creates a magnetic field.
•     Accelerated Charge produces electromagnetic waves.

Accelerating/ deaccelerating charge cause kink(deformation) in Electric Field. All electric filed don’t get adjusted according to new fields and repels the old one and thus it forces them to move forward. They sustain themselves by principle that changing magnetic and electric filed generates electric and magnetic fields.

In good conductor, there is high attenuation of EM wave hence it can’t propagate through good conductor and this attenuation increase with frequency.

 

We will talk about more properties of EM waves in our upcoming post.

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