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# Ch16 - Chapter 16 Temperature and Heat Temperature and...

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Chapter 16: Temperature and Heat Temperature and thermal equilibrium Temperature • is a measure of how hot or cold an object is • is measured by a thermometer Thermal equilibrium Objects placed in contact will eventually reach the same temperature. When this happens, they are in thermal equilibrium. Zero’th law of thermodynamics If an object C is in thermal equilibrium with both objects A and B, Then A and B are in thermal equilibrium with each other too.

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Temperature and thermal equilibrium (cont’d) Thermometer • Thermometers are devices used to measure the temperature of an object or a system. • When a thermometer is in thermal contact with a system, energy is exchanged until the thermometer and the system are in thermal equilibrium with each other. • All the thermometers use some physical properties that depend on the temperature. Some of these properties are: 1) the volume of a fluid 2) the length of a solid 3) the pressure of a gas held at constant volume 4) the volume of a gas held at constant pressure 5) electric resistance of a conductor 6) the color of very hot object.
Temperature and thermal equilibrium (cont’d) Thermometer (cont’d) • One common thermometer consists of a mass of liquid: mercury or alcohol. The fluid expands into a glass capillary tube when its temperature rises. • When the cross-sectional area of the tube is constant, the change in volume of the liquid varies linearly with its length along the tube. • The thermometer can be calibrated by placing it in thermal contact with environments that remain at constant temp. • Two of such environments are: 1) a mixture of water and ice in thermal equilibrium at atmospheric pressure. 2) a mixture of water and steam in thermal equilibrium at atmospheric pressure. 0 o C (Celsius) 100 o C Freezing point Boiling point

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Temperature and its scales Constant-volume gas thermometer and the Kelvin scale • A constant-volume gas thermometer measures the pressure of the gas contained in the flask immersed in the bath. The volume of the gas in the flask is kept constant by raising or lowering reservoir B to keep the mercury level constant in reservoir A.
Temperature and its scales (cont’d) Constant-volume gas thermometer and the Kelvin scale • It has been experimentally observed that the pressure varies linearly with temperature of a fixed volume of gas, which does not depend on what gas is used. • It has been experimentally observed that these straight lines merge at a single point at temp. -273.15 o C at pressure = 0. This temperature is called absolute zero, which is the base of the Kelvin temperature scale T=T C -273.15 measured in kelvin (K) where T C is temperature in Celsius. . 0 K = -273.15 o C

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Temperature and its scales (cont’d) Gas thermometer and absolute (Kelvin) scale (cont’d) The pressure of any gas at constant volume is a linear function of temperature, which always extrapolates to zero at –273.15 ºC.
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