Question

What are primary and secondary sources of light?

Answer 1

1. Primary sources of light: 
   The sources that emit light of their own is called primary sources. The emission of light may be due to
   
   • the high temperature of the source,
     e.g., the Sun, the stars, objects heated to high temperature, a flame, etc.
   • the effect of current being passed through them,
     e.g., tubelight, TV, etc.
   • chemical or nuclear reactions
     e.g., firecrackers, nuclear energy generators, etc.
2. Secondary sources of light:
   
   • Secondary sources are those sources that do not produce light of their own but receive light from some other source and either reflect or scatter it around.
   • e.g. the moon, the planets, objects such as humans, animals, plants, etc. which we see due to reflected light.
   • Majority of the sources that we see around are secondary sources and most of them are extended sources.