Physics
Stationary wave is formed by

A transverse wave superposing a longitudinal wave
Two waves of same frequency travelling in the opposite direction
Two waves of same frequency travelling in the same direction
Two waves of the same speed superposing

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

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