We have already that sunlight consists of all the colors seen in a rainbow. These colors ate violet, indigo, blue, green, yellow, orange and red. Light from the sun travels in the form of waves, which are known as electromagnetic waves. The human eye cannot perceive the entire band of wavelengths but can perceive those relating to these seven colors only. Rays having wavelengths higher than that of red light are called infrared rays and those lower than violet light are called ultraviolet rays. Both infrared and ultraviolet rays are not visible to our eyes.
Infrared Rays from the Sun
Infrared rays come not only from the sun, but also all hot objects. Infrared rays were discovered by the British astronomer sir William Herschel in 1800. burning wood and coal electric heater all produce these rays. In fact all the objects emit infrared rays depending on their temperature. Warmer objects emit more infrared rays than cooler ones. These can be recorded on special type of photographic films made of infrared sensitive materials. Whenever these rays fall on any material body they produce heat.
Infrared radiations are used for the treatment of several diseases. Special types of infrared lamps are used for the treatment of muscle and joint aches especially back pain. They are also used for heating rooms in winters.
Infrared radiations are used for the guidance and control of missiles and other ballistic weapons. These radiations are also used for transmitting and receiving invisible signals. Molecular structures are studied with the help of these radiations.
These rays can also detect impurities present in materials. Infrared absorption spectroscopy is important analytical tool in organic chemistry.