If hot air rises , why is it cooler at the top of mountain than near t

1.	If hot air rises , why is it cooler at the top of mountain than near the sea level?
Answer» Since atmospheric pressure decreases with height, pressure at the top of the mountain is lesser. When the hot air rises up,it suffer adiabatic expansion at the top of the mountain.For an adiabatic change,first law of thermodynamics may be express as dU + dW =0 (dQ = 0) dW = -dU Therefore work done by the air in rising up (dW =+ve ) result in decrease in the internal Energy of the air (dU = -ve) and hence a fall in the temperature.

If hot air rises , why is it cooler at the top of mountain than near the sea level?

Answer»

Since atmospheric pressure decreases with height, pressure at the top of the mountain is lesser. When the hot air rises up,it suffer adiabatic expansion at the top of the mountain.For an adiabatic change,first law of thermodynamics may be express as

dU + dW =0 (dQ = 0)

dW = -dU

Therefore work done by the air in rising up (dW =+ve ) result in decrease in the internal

Energy of the air (dU = -ve) and hence a fall in the temperature.

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If hot air rises , why is it cooler at the top of mountain than near the sea level?

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