## Radio Waves – Class 12 | Chapter – 8 | Physics Short Notes Series PDF for NEET & JEE

Radio Waves: Radio waves are a type of electromagnetic radiation with frequencies ranging from about 3 kHz to 300 GHz. They were discovered by James Clerk Maxwell in the 19th century and are used for various applications such as communication, broadcasting, navigation, and radar. Radio waves are generated by oscillating electric charges, which create time-varying electric and magnetic fields. These fields propagate through space as waves and can be detected and processed by various devices.

Radio waves are a type of electromagnetic radiation with wavelengths ranging from about 1 millimeter to 100 kilometers, and frequencies ranging from about 3 kilohertz to 300 gigahertz. Here are some of the key properties of radio waves:

• Wavelength: The wavelength of a radio wave is the distance between two consecutive peaks or troughs. Longer waves have lower frequencies, while shorter waves have higher frequencies.
• Frequency: The frequency of a radio wave is the number of cycles per second, measured in hertz. Higher frequency waves have more energy and can carry more information.
• Speed: Radio waves travel at the speed of light, which is approximately 300,000 kilometers per second in a vacuum.
• Polarization: These waves can be polarized, which means that the electric field oscillates in a particular direction. Polarization can be either linear or circular.
• Propagation: These waves can propagate through various media, such as air, water, and even solid objects. They can be reflected, refracted, diffracted, and absorbed, depending on the properties of the medium they are passing through.
• Modulation: These waves can be modulated to carry information, such as voice or data. Common modulation techniques include amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM).
• Interference: These waves can interfere with each other, either constructively or destructively, depending on their phase and amplitude. This can lead to signal distortion or noise.
• Applications: These waves are used in many applications, including radio and television broadcasting, satellite communication, radar, GPS, wireless communication, and medical imaging.

Band name Abbreviation ITU band number Frequency and wavelength
Tremendously low frequency TLF 1–3 Hz
300,000–100,000 km
Extremely low frequency ELF 1 3–30 Hz
100,000–10,000 km
Super low frequency SLF 2 30–300 Hz
10,000–1,000 km
Ultra low frequency ULF 3 300–3,000 Hz
1,000–100 km
Very low frequency VLF 4 3–30 kHz
100–10 km
Low frequency LF 5 30–300 kHz
10–1 km
Medium frequency MF 6 300–3,000 kHz
1,000–100 m
High frequency HF 7 3–30 MHz
100–10 m
Very high frequency VHF 8 30–300 MHz
10–1 m
Ultra high frequency UHF 9 300–3,000 MHz
100–10 cm
Super high frequency SHF 10 3–30 GHz
10–1 cm
Extremely high frequency EHF 11 30–300 GHz
10–1 mm
Terahertz or tremendously high frequency THF 12 300–3,000 GHz
1–0.1 mm

Radio waves have many applications in modern technology, including:

• Radio and television broadcasting: These waves are used to transmit signals from radio and television stations to receivers in homes and vehicles, allowing people to listen to music, news, and entertainment.
• Satellite communication: These waves are used to communicate with satellites in space, allowing for global communication, navigation, and remote sensing.
• Radar: These waves are used in radar systems to detect the presence, distance, and speed of objects, and are used in military, aviation, and weather forecasting applications.
• GPS: Global Positioning System (GPS) uses radio waves to determine the location and speed of vehicles and people, and is used in navigation, geolocation, and tracking applications.
• Wireless communication: These waves are used in wireless communication systems, such as cellular networks, Wi-Fi, and Bluetooth, allowing for mobile communication and data exchange.
• Medical imaging: These waves are used in medical imaging techniques, such as magnetic resonance imaging (MRI), which uses strong magnetic fields and radio waves to create detailed images of the body.
• Radio astronomy: These waves are used in astronomy to study the universe, including the study of cosmic microwave background radiation, pulsars, and other celestial objects.

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