Radio Waves (10^{3}–10^{9} Hz, wavelengths up to 10^{5} m) Source: oscillating electric circuits and antennas. Used in AM/FM radio broadcasting, television transmission, and mobile communications. Detected by antenna-receiver circuits. Long wavelengths allow them to diffract around obstacles and follow Earth's curvature.

Microwaves (10^{9}–10^{12} Hz, mm to cm wavelengths) Source: magnetron and klystron vacuum tubes. Key applications: RADAR (transmit microwaves, detect reflections from objects for ranging and tracking), microwave ovens (magnetron microwaves rotate water molecules → heat), satellite communication (microwaves penetrate the ionosphere, enabling direct communication with satellites). Detected by point contact diodes.

Infrared Radiation (10^{12}–$4 \times 10^{14}$ Hz, 700 nm to 1 mm) Source: all hot bodies (thermal radiation). Applications: night vision devices (detect IR emitted by warm objects in dark), physiotherapy lamps (deep tissue heating for pain relief), remote controls (IR LEDs), greenhouse effect (glass/atmosphere transmits visible but absorbs IR, trapping heat). Detected by thermopiles, bolometers, and IR cameras.

Visible Light ($4 \times 10^{14}$–$7.5 \times 10^{14}$ Hz, 400–700 nm) Source: Sun, electric bulbs, LEDs, lasers. Applications: human vision (eye photoreceptors sensitive to 400–700 nm), plant photosynthesis (chlorophyll absorbs red 680 nm and blue 430 nm), photography, optical fibre communication. Detected by human eye, photocells, photographic film, CCD sensors.

Ultraviolet Radiation ($7.5 \times 10^{14}$–10^{17} Hz, 10–400 nm) Source: Sun, mercury vapour lamps, excimer lasers. Applications: sterilisation (UV destroys microorganism DNA — hospitals, water treatment), LASIK eye surgery (UV excimer lasers reshape cornea), vitamin D synthesis (skin converts 7-dehydrocholesterol under UV exposure). Detected by photocells and UV-sensitive photographic film.

X-rays (10^{16}–10^{21} Hz, picometres to nanometres) Source: Coolidge tube (fast electrons striking tungsten target — bremsstrahlung + inner-shell transitions). Applications: medical X-ray imaging (bone fractures, chest X-rays — bone absorbs, soft tissue transmits), CT scans (multiple-angle imaging reconstructed by computer), crystal diffraction/Bragg spectroscopy (wavelength ~0.1 nm matches inter-atomic spacings). Detected by photographic film, digital flat-panel detectors, Geiger counters.

Gamma Rays (10^{18}–10^{24} Hz, sub-picometres) Source: radioactive nuclear decay and nuclear reactions. Applications: cancer radiotherapy (targeted gamma beams destroy tumour cells — gamma knife), sterilisation of medical equipment (gamma irradiation kills all microorganisms), nuclear medicine PET scans. Detected by Geiger counters, scintillation detectors, ionisation chambers.