Physics
Purpose of an optical filter is to

Refract light of different colours
Reflect lights of different colours
Dispense light into component colours
Transmit or absorb light of different colours

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Physics
It is dangerous to observe Solar eclipse with naked eyes because

Infrared radiations from sun burn our retina
All radiations from sun initiate chemical reactions in eyes
Cosmic rays reach eyes more during the eclipse
Ultraviolet radiations from Sun burn our retina

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