Question:

Answer the following: (a) The triple-point of water is a standard fixed point in modern thermometry. Why? What is wrong in taking the melting point of ice and the boiling point of water as standard fixed points (as was originally done in the Celsius scale )? (b) There were two fixed points in the original Celsius scale as mentioned above which were assigned the number 0oC and 100oC respectively. On the absolute scale one of the fixed points is the triple-point of water, which on the kelvin absolute scale is assigned the number 273.16 K. What is the other fixed point on this (kelvin) scale? (c) The absolute temperature (Kelvin scale ) T is relate to the temperature tc​ on the Celsius scale by tc​=T−273.15. Why do we have 273.15 in this relation and not 273.16? (d) What is the temperature of the triple-point of water on an absolute scale whose unit interval size is equal to that of the Fahrenheit scale ?

Answer:

A. (a) The triple-point of water is a standard fixed point in modern thermometry because it is the point at which all three states of water (solid, liquid, and gas) exist in equilibrium. Taking the melting point of ice and the boiling point of water as standard fixed points is not accurate because the actual temperatures of these points vary depending on the atmospheric pressure.

B. The other fixed point on the kelvin absolute scale is absolute zero, which is assigned the number 0 K.

C. We have 273.15 in the relation because it is the exact temperature of the triple-point of water on the Celsius scale.

D. The temperature of the triple-point of water on an absolute scale whose unit interval size is equal to that of the Fahrenheit scale is 459.67°F.

Question:

Two ideal gas thermometers A and B use oxygen and hydrogen respectively. The following observations are made Temperature Pressure thermometer A Pressure thermometer B Triple-point of water 1.250×10^5Pa 0.200×10^5Pa Normal melting point of sulphur 1.797×10^5Pa 0.287×10^5Pa (a) What is the absolute temperature of normal melting point of sulphur as read by thermometers A and B ? (b) What do you think is the reason behind the slight difference in answers of thermometers A and B ? (The thermometers are not faulty) What further procedure is needed in the experiment to reduce the discrepancy between the two readings ?

Answer:

(a) The absolute temperature of normal melting point of sulphur as read by thermometer A is 273.15 K and as read by thermometer B is 253.15 K.

(b) The reason behind the slight difference in answers of thermometers A and B is that oxygen and hydrogen have different thermodynamic properties. To reduce the discrepancy between the two readings, the experiment should be repeated with a higher number of pressure and temperature readings to ensure that the data is accurate.