Physics
Radiocarbon is produced in the atmosphere as a result of

Action of solar radiations particularly cosmic rays on carbon dioxide present in the atmosphere.
Collision between fast neutrons and nitrogen nuclei present in the atmosphere.
Lightning discharge in atmosphere.
Action of ultraviolet light from the sun on atmospheric oxygen.

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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

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

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