Measurement of Temperature

Measurement of Temperature:

Measurement of temperature requires:

(a) the construction of an instrument (i.e., thermometer)

(b) the calibration of the thermometer.

The construction of a thermometer depends on some physical property of matter (such as pressure, volume, emf, resistance etc) that changes with temperature.

The calibration of the thermometer depends on fixing certain points on the thermometer.

The fixed points are (the ice point) the temperature of the melting point of ice and (the steam point) the temperature of the boiling point of water under normal atmospheric pressure.

Thermometric Scales :

The distance between the LFP and UFP of a thermometer is called the fundamental interval.

Fundamental interval = (UFP) – (LFP)

The fundamental interval is divided into equal parts. These parts are given arbitary numerical values of temperature known as the thermometric scale.

The Celsius(°C), Fahrenheit(°F), Kelvin(K), Reaumur(R), Rankine(R_a) are commonly used thermometric scales.

Different Thermometric Scales:

Thermometric scale	LFP	UFP	Total No. of divisions
Celsius scale	0°C	100°C	100
Fahrenheit scale	32°F	212°F	180
Kelvin scale (or) Absolute scale	273.15K	373.15K	100
Reaumur scale	0°R	80°R	80

On any thermometric scale

= constant

(or)

= constant

Relation Between Temperatures of Different Scales:

The temperature difference on different scales is

Common reading on Celsius and Fahrenheit scales is –40° i.e. –40°C = –40°F

Since,

X = –40°

The temperature of the core of the sun is 107K while its surface is 6000K. The normal temperature of the human body is 310.15K (= 37°C = 98.6°F) while NTP implies 273.15K (= 0°C = 32°F).