c + . and the assignment T = . K for the triple point of water are exact relations (by choice). With this choice, the Celsius temperature of the melting point of water and boiling point of water (both at atm pressure) are very close to, but not exactly equal to ° C and ° C respectively.
In the original Celsius scale, these latter fixed points were exactly at ° C and ° C (by choice), but now the triple point of water is the preferred choice for the fixed point, because it has a unique temperature. . A liquid in equilibrium with vapour has the same pressure and temperature throughout the system; the two phases in equilibrium differ in their molar volume (i.e. density).
This is true for a system with any number of phases in equilibrium. . Heat transfer always involves temperature difference between two systems or two parts of the same system. Any energy transfer that does not involve temperature difference in some way is not heat.
. Convection involves flow of matter within a fluid due to unequal temperatures of its parts. A hot bar placed under a running tap loses heat by conduction between the surface of the bar and water and not by convection within water. EXERCISES .
The triple points of neon and carbon dioxide are . K and . K respectively. Express these temperatures on the Celsius and Fahrenheit scales.
. Two absolute scales A and B have triple points of water defined to be A and B. What is the relation between T A and T B ? .
The electrical resistance in ohms of a certain thermometer varies with temperature according to the approximate law : R = R o [ + α ( T – T o )] The resistance is . Ω at the triple-point of water . K, and . Ω at the normal melting point of lead ( .
K). What is the temperature when the resistance is . Ω ? .
Answer the following : (a) The triple-point of