Any form of wave is a movement of energy from one place to another with oscillatory motion. The type of wave which has an electric field and a magnetic field is known as an electromagnetic wave. There are seven different forms of electromagnetic waves, which are collectively known as the electromagnetic spectrum. Each of these waves has a distinct wavelength and frequency. The frequency range starts from 104 Hertz and extends up to 1024 Hertz. The biggest natural source of electromagnetic waves on Earth is sunlight. Rays of the sun travel through different layers of Earth’s atmosphere to reach the surface of Earth. 

Properties & behaviours of electromagnetic waves

• The energy transferred through the movement of electromagnetic waves is known as electromagnetic radiation.
• Visible light, X-ray, microwave, infrared, ultraviolet, gamma rays, radio waves are the seven unique members of the electromagnetic spectrum.
• Visible light comes in the mid-range of this spectrum.
• Based on the movement, waves are of two types – longitudinal waves and transverse waves. Electromagnetic waves fall under the second category. That means that it oscillates in the direction perpendicular to its actual path of movement. 
• In vacuum conditions, electromagnetic waves travel at a constant speed of 3,00,000 km/s approximately. 
• These waves can travel without any medium of propagation. 
• Electromagnetic waves reflect when interrupted by any reflective surface.
• Electromagnetic waves can be refracted. That means, while travelling from one medium to another, it tends to bend its path of movement. 

Uses of Electromagnetic Waves

Electromagnetic waves are useful in many different ways;

• Radio waves are used for communication.
• Microwave is used in cooking ovens.
• X-ray is used for photo imaging the internal parts of our body, like fractures in bones. 
• Gamma rays are harmful to human life. However, it can be effectively used in a controlled manner. It is used in nuclear energy plants, in the treatment of cancer (radiotherapy), and also for the purpose of high-level sterilisation. 
• Ultraviolet radiation has an ionising effect. It can produce free radicals. When atmospheric gases are ionised by the UV rays of the sun, it becomes an ideal medium for radio wave communication. However, direct exposure to UV rays causes damage to our skin and leads to problems like sunburns and suntan. 

Layers of Earth’s Atmosphere & their Functions

We all know, the surface of Earth is covered by a thick blanket of a mixture of gases called the atmosphere. Atmospheric gases include – oxygen, nitrogen, carbon dioxide, argon, etc., and also some water vapour. There are 5 distinct layers of the earth’s atmosphere:

1. The Troposphere: This is nearest to the earth’s surface. The density of the air is highest in this layer. 
2. The Stratosphere – The ozone layer that protects us from the harmful ultraviolet radiation emitted by the sun can be found here. 
3. The Mesosphere – Combustion of the meteors, which we see as sudden flashes of light during the night, happens in this region. 
4. The Thermosphere – The ionosphere, which is essential for communication on Earth through radio waves, can be found here. 
5. The Exosphere – This is the topmost layer of the atmosphere. Air density is extremely low in this layer. 

The function of the ionosphere 

The ionosphere lies between 60 – 300 km from Earth’s surface. The ionosphere is formed because atoms and molecules present in this layer get converted into free radicals by the sunlight. This process is called photo-ionisation. These free ions, in turn, facilitate the movement of the radio waves and make long-distance communication possible.

The ionosphere consists of 3 different regions – 

1. D-region: This is the lowermost portion of the ionosphere. Radio signals mostly pass through this region uninterrupted. 
2. E-region: The first-ever transmission of radio signals made by Marconi for wireless communication happened in this region. 
3. F-region: The density of charged particles is maximum in the F region. Most transmissions of radio signals happen from this particular region. 

Role of F-region In Radio Transmission

The F-region of the ionosphere is often referred to as the Appleton–Barnett layer. It is named after two renowned scientists – English physicist Edward Appleton and New Zealand physicist Miles Barnett. 

Edward Appleton is credited for his discovery of the existence of the ionosphere in Earth’s atmosphere. Miles Barnett is credited for his extensive studies on the propagation of radio waves. 

During the daytime, F-region segregates into two different layers: 

1. F1 layer: The F1 layer can be found between 130-220 km above sea level. The F1 layer lies in the lower part of the F region. It is considered a secondary layer because it disappears at night.
2. F2 layer: The F2 layer can be between 220-800 km above sea level. It is the topmost portion of the ionosphere. This is a permanent layer and does not disappear during the night. 

Important Facts about F2 Layer of the Ionosphere

• The electron density in the F2 layer is very high. 
• Unlike the F1 layer, which functions only during the daytime, the F2 layer can propagate radio signals all through the day. Thus, it can be said it is more reliable in comparison to the F1 layer. 
• It has the capacity to cover a wider range of broadcast areas than the E-region or even the F1 layer. 
• The charged particles present in the F2 layer can reflect back radio signals to Earth only when the frequency of the radio wave is within a specified range. 
• Radio waves that have a frequency under 30 megahertz can be sent back to Earth effectively. 
• This layer is most suitable for long-range radio transmission. 
• The strength of radio transmission in the F2 layer is at its peak during noontime and it is at its lowest just before sunrise. 
• Signals of FM radio are propagated through this F2 layer. 
• Other forms of radio propagation that are possible through the F2 layer are that of television, amateur radio, mobile, etc. 

Conclusion

To summarise the topic, electromagnetic waves – Layers of Earth’s atmosphere – F2 layer, here are some of the important points you should remember: 

• An electromagnetic wave is formed with an electric field and a magnetic field.
• The energy transferred through the movement of electromagnetic waves is known as electromagnetic radiation.
• A zone in the thermosphere layer is named the ionosphere because it contains a high level of free electrons and free radicals. These ionic particles facilitate the deflection of radio signals sent from Earth and thus contribute to radio communication. 
• Maximum radio communication happens through the F-region of the ionosphere. In this region, the F2 layer present is most suitable for long-range radio transmission.