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 .