Physics · Electromagnetic Waves · NEET
Radio waves are the LONGEST electromagnetic waves. Their wavelength is greater than about 0.1 m and can go up to hundreds of metres (AM radio ~10^2 m). Since wavelength and frequency are inversely related (c = f x wavelength), radio waves also have the LOWEST frequency (below ~10^9 Hz) and the LOWEST energy in the whole EM spectrum. Order to remember: radio (longest) > microwave > infrared > visible > UV > X-ray > gamma (shortest).
Radio waves are produced by accelerating charges. In practice, charges are made to oscillate (speed up and slow down) in an electrical circuit called an oscillator or LC circuit connected to an antenna. The oscillating current in the antenna means charges accelerate back and forth, and every accelerating charge radiates EM waves. The frequency of the radio wave equals the frequency of oscillation of the charges in the circuit.
Radio waves have frequencies from a few hertz up to about 10^9 Hz (1 GHz), and wavelengths longer than about 0.1 m. For NEET matching questions, remember AM radio waves are around 10^2 m (long), and this is the longest-wavelength band. Anything shorter than ~0.1 m and around the cm range is a microwave, not a radio wave.
Radio waves are ideal for communication because they can travel long distances, can be reflected by the ionosphere (for AM ground/sky waves), and pass easily through air and even walls. Information (sound) is added to a radio wave by modulation (AM = amplitude modulation, FM = frequency modulation). This is why radio waves carry AM and FM radio, TV signals and the carrier waves in mobile phones.
No. Both are low-energy EM waves, but microwaves have shorter wavelength (about 10^-2 m, the cm range) and higher frequency (~10^9 to 10^11 Hz) than radio waves (wavelength >0.1 m). Radio waves are made by oscillating LC circuits/antennas, while microwaves are produced by special vacuum tubes called klystrons and magnetrons. NEET matching questions often test exactly this difference.
Yes. Photon energy is E = hf, so lower frequency means lower energy. Radio waves have the lowest frequency of all EM waves, so their photons carry the least energy. This is why radio waves are non-ionising and harmless, while high-frequency waves like X-rays and gamma rays are dangerous.
Match List I (Electromagnetic waves) with List II (Wavelength): (a) AM radio waves (b) Microwaves (c) Infrared waves (d) X-rays; (i) 10^-10 m (ii) 10^2 m (iii) 10^-2 m (iv) 10^-4 m. Choose the correct match.
Match List-I with List-II: P. Microwave Q. UV rays R. Gamma rays S. Radio wave; I. For purifying the water II. For warming the food III. For AM and FM communication systems IV. For treating the cancer cells. The correct option is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Radio waves are used for AM and FM radio broadcasting, television transmission, mobile phone carrier signals, and radio astronomy. They are chosen because they travel far, pass through the atmosphere and buildings, and can be reflected by the ionosphere.
They are produced by accelerating charges in an oscillating LC circuit connected to an antenna. The charges oscillate back and forth, and every accelerating charge radiates EM waves at the same frequency as the oscillation.
Radio waves have wavelengths greater than about 0.1 m, ranging up to hundreds of metres. AM radio waves are around 10^2 m, making radio the longest-wavelength band of the EM spectrum.
Photon energy is E = hf. Radio waves have the lowest frequency of all EM waves, so hf is smallest, giving them the least energy. This makes them non-ionising and safe.
AM (amplitude modulation) varies the amplitude of the carrier radio wave to carry sound, while FM (frequency modulation) varies its frequency. Both use radio waves as the carrier; FM gives clearer sound and AM travels farther via the ionosphere.
