Physics
Purpose of an optical filter is to

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

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Physics
On a cold day when a room temperature is 15oC, the metallic cap of a pen becomes much colder than its plastic body, though both are at the same temperature of 15oC, because

plastics have a higher thermal conductivity than metals
metals have higher thermal capacity than plastics
metals are good conductor of heat
plastics have a lower density than metals

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