Question

when the uv rays come on the surface of earth then heat is trapped by the earth and light is not.why?

Answer 1

The radiation received from Sun on the surface of  EArth contains  UV rays, visible light, infra red, and much more above UV rays and much less than infra red rays also.

UV rays are absorbed by the atmosphere - the energy in them is suitable for the excitation of atmospheric gases and materials present there.  The absorbed UV rays again cause excitation of atoms and release of energy (radiation) in different directions.

Energy present in the light rays and infra red is less.  Some a little light energy is absorbed and the remaining falls on the surface of Earth.

Answer 2

all types of electro magnetic radiations emit out energy.the sun radiates all types of radiations but the radiations such as uv,ir are not visible but are very powerful rations.the uv radiations are absorbed by the atmospheric gases for the excitation process and the visible ligth radiations are not so they are reflected back.so only the heat is trapped my earth but not light