Q.Write four uses of Electromagnetic waves.

The full electromagnetic spectrum is the orderly classification of every possible electromagnetic wave by wavelength or frequency (related by $c=f\lambda$ in vacuum), running continuously from the longest-wavelength, lowest-frequency radio waves to the shortest-wavelength, highest-frequency gamma rays, with visible light forming only a narrow band roughly in the middle. Radio waves (a few Hz to $10^9$ Hz) are produced by accelerated charges oscillating in conducting wires (antennas), show reflection and diffraction, and carry radio and television broadcasts and cellular voice communication in the UHF band. Microwaves ($10^9$ to $10^{11}$ Hz) are produced by specialised vacuum-tube devices -- the klystron, the magnetron, and the Gunn diode -- undergo reflection and can be polarised, and are used in radar for aircraft navigation and vehicle-speed detection, in microwave ovens, and for long-distance satellite communication. Infrared radiation ($10^{11}$ to $4\times10^{14}$ Hz), sometimes called heat radiation, is produced by hot bodies and by molecules undergoing rotational and vibrational transitions, and is used in infrared detectors aboard Earth satellites for military surveillance and to observe crop growth, in night-vision/infrared photography, in physiotherapy for muscular strain, to maintain the Earth's warmth through the greenhouse effect, and in remote controls for TVs and other appliances. Visible light ($4\times10^{14}$ to $8\times10^{14}$ Hz) is produced by incandescent bodies and by excited atoms in gases, obeys the ordinary laws of reflection and refraction, shows interference, diffraction, polarisation and the photoelectric effect, and is what produces the sensation of vision -- it is also used to probe molecular structure and the arrangement of electrons in the outer shells of atoms. Ultraviolet radiation ($8\times10^{14}$ to $10^{17}$ Hz), from the Sun, arcs and ionized gases, sterilises instruments and destroys bacteria, drives burglar alarms, reveals invisible writing and fingerprints, and aids atomic-structure study, though most is absorbed by atmospheric ozone and can be harmful to the human body. X-rays ($10^{17}$ to $10^{19}$ Hz), produced by suddenly stopping high-speed electrons at a high-atomic-number target or by tr …