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Home » (a) The triple-point of water is a standard fixed point in modern thermometer. 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 C elsius scale as mentioned above which were assigned the number and , 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 What is the other fixed point on this (Kelvin) scale?
(a) The triple-point of water is a standard fixed point in modern thermometer. 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 C elsius scale as mentioned above which were assigned the number 0^{\circ} \mathrm{C} and 100^{\circ} \mathrm{C}, 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 \mathrm{~K} . What is the other fixed point on this (Kelvin) scale?
CBSE | Class 11 | NCERT | Thermal Properties of Matter
(a) The triple-point of water is a standard fixed point in modern thermometer. 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 C elsius scale as mentioned above which were assigned the number 0^{\circ} \mathrm{C} and 100^{\circ} \mathrm{C}, 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 \mathrm{~K} . What is the other fixed point on this (Kelvin) scale?

Solution:

i) Due to the fact that the melting and boiling points of water fluctuate with changes in pressure, the temperature of the triple point of water is not considered to be a standard fixed point. However, the temperature of the triple point of water is unique and does not vary with changes in pressure.

(ii) On the Kelvin scale, there is just one fixed point, which is 273.16 K at the lower end of the scale; the top fixed point is not there.

i

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