Absolute zero |
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It is found that the volume of a gas at constant pressure is proportional to the temperature if the zero of temperature is taken as -273.15 °C. The volume-temperature data points fit a straight line more closely when the chosen fixed pressure is very low. An ideal gas is an imaginary gas for which volume is exactly proportional to temperature for any constant pressure at all temperatures. The absolute temperature scale is named after Lord Kelvin. Zero Kelvin (-273.15 °C) is absolute zero.
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Measurements can be made with a narrow glass tube sealed at the bottom and closed with a bead of mercury half way down. The glass tube is immersed in water (or oil). As the temperature is increased the mercury bead slides up the tube keeping the pressure in the trapped air column constant at one atmosphere. The length of the air column is found to be proportional to the absolute temperature. |