(i) The orderly distribution of electromagnetic waves (on the basis of wavelength or frequency) in the form of distinct groups having widely differing properties is called the electromagnetic spectrum.

The following table gives a complete and detailed picture of electromagnetic spectrum

(ii) Various parts of electromagnetic spectrum :

(i) The gaseous envelop surrounding the earth is called earth’s atmosphere.

(ii) It mainly consists of nitrogen 78% and oxygen 21% alongwith a little portion of argon, carbon-di-oxide, water vapour, hydrocarbons, sulphur compounds and dust particles.

(iii) The density of atmospheric air goes on decreasing gradually as we go up.

(iv) The earth’s atmosphere has no sharp boundary.

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