Type | Range | Uses |
Radio | > 0.1 m | used in radio and television communication systems |
Microwave | 0.1m to 1 mm | Due to their short wavelengths, they are suitable for the radar systems used in aircraft navigation. Microwave ovens. |
Infra-red | 1 mm to 700 nm | widely used in the remote switches of household electronic systems, used in physical therapy. Infrared radiation also plays an important role in maintaining the earth’s warmth or average temperature through the greenhouse effect. |
Light | 700 nm to 400 nm | Our eyes are sensitive to this range of wavelengths. |
Ultraviolet | 400 nm to 1 nm | Due to its shorter wavelengths, UV radiations can be focussed into very narrow beams for high precision applications such as LASIK (Laser assisted in situ keratomileusis) eye surgery. UV lamps are used to kill germs in water purifiers |
X-rays | 1 nm to 10 ^ –3 nm | used as a diagnostic tool in medicine and as a treatment for certain forms of cancer. |
Gamma rays | < 10 ^ –3 nm | used in medicine to destroy cancer cells. |
Radio Waves:
They are generally in the frequency range from 500 kHz to about 1000 MHz. The AM (amplitude modulated) band is from 530 kHz to 1710 kHz. Higher frequencies upto 54 MHz are used for short wave bands. TV waves range from 54 MHz to 890 MHz. The FM (frequency modulated) radio band extends from 88 MHz to 108 MHz.
Microwave:
Due to their short wavelengths, they are suitable for the radar systems used in aircraft navigation. Radar also provides the basis for the speed guns used to time fast balls, tennis serves, and automobiles.
Microwave ovens are an interesting domestic application of these waves. In such ovens, the frequency of the microwaves is selected to match the resonant frequency of water molecules so that energy from the waves is transferred efficiently to the kinetic energy of the molecules. This raises the temperature of any food containing water.
Infrared:
Infrared waves are sometimes referred to as heat waves. This is because water molecules present in most materials readily absorb infrared waves (many other molecules, for example, CO2, NH3, also absorb infrared waves). After absorption, their thermal motion increases, that is,
they heat up and heat their surroundings.
Infrared lamps are used in physical therapy.
Infrared radiation also plays an important role in maintaining the earth’s warmth or average temperature through the greenhouse effect. Incoming visible light (which passes relatively easily
through the atmosphere) is absorbed by the earth’s surface and reradiated as infrared (longer wavelength) radiations. This radiation is trapped by greenhouse gases such as carbon dioxide and water vapour. Infrared detectors are used in Earth satellites, both for military purposes and to observe growth of crops.
Electronic devices (for example semiconductor light emitting diodes) also emit infrared and are widely used in the remote switches of household electronic systems such as TV sets, video recorders and hi-fi systems.
Ultraviolet:
UV light in large quantities has harmful effects on humans. Exposure to UV radiation induces the
production of more melanin, causing tanning of the skin. UV radiation is absorbed by ordinary glass. Hence, one cannot get tanned or sunburn through glass windows.
Due to its shorter wavelengths, UV radiations can be focussed into very narrow beams for high precision applications such as LASIK (Laser assisted in situ keratomileusis) eye surgery. UV lamps are used to kill germs in water purifiers.