The arranged array of electromagnetic radiations in the sequence of their wavelength or frequency is called electromagnetic spectrum
Radio and microwaves are used in radio and TV communication,
Infrared rays are used to
( i) Treat muscular straw.( ii) For taking photographs’ in fog or smoke.( iii) In green house to keep plants warm.( iv) In weather forecasting through infrared photography.
Ultraviolet rays are used
( i) In the study of molecular structure.( ii) In sterilizing the surgical instruments.( iii) In the detection of forged documents, £ ringer prints.
X-rays are used
( i) In detecting faults, cracks, flaws and holes in metal products.( ii) In the study of crystal structure.( iii) For the detection of pearls in oysters.
γ – rays are used for the study of nuclear structure.
Earth’ s Atmosphere
The gaseous envelope surrounding the earth is called earth’ s atmosphere. It contain the following layers
( i) Troposphere This region extends upto a height of 12 km from earth’ s surface.
( ii) Stratosphere This region extends from 12 km to 50 km. In this region, most of the atmospheric ozone is concentrated from 30 to 50 km. This layer is called ozone layer.
( iii) Mesosphere The region extends from 50 km to 80 km.