Physics
Red light is used for signals because it has

Long wavelength
Low refraction in the medium
High intensity
High frequency

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Physics
A stone floor feels cold to the bare feet but a carpet on the same floor feels warm. This is because

The floor and carpet are at different temperatures
The stone conveys the heat away from the feet more rapidly than the carpet
The human body maintains a constant temperature
The carpet is a better conductor of heat than the stone

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