Temperature is measured using a thermometer. Many physical properties of materials change sufficiently with temperature. A physical property that changes with temperature is called a thermometric property. When a thermometer is put in contact with a hot body, the mercury expands, increasing the length of the mercury column.

Thermometers are calibrated so that a numerical value may be assigned to a given temperature in an appropriate scale. The two familiar temperature scales are the Fahrenheit temperature scale and the Celsius temperature scale.

Celsius Scale: It defines ice-point temperature as \(0^{\circ} \mathrm{C}\) and the steam point temperature as \(100^{\circ} \mathrm{C}\) on the Celsius scale. The space between \(0^{\circ} \mathrm{C}\) and \(100^{\circ} \mathrm{C}\) marks is equally divided into 100 intervals.

Fahrenheit Scale: It defines the ice-point temperature as \(32^{\circ} \mathrm{F}\) and the steam point temperature as \(212^{\circ} \mathrm{F}\) on the Fahrenheit scale. The space between \(32^{\circ} \mathrm{F}\) and \(212^{\circ} \mathrm{F}\) is divided into 180 equal intervals.

A relationship for converting between the two scales may be obtained from a graph of Fahrenheit temperature \(\left(t_{\mathrm{F}}\right)\) versus celsius temperature \(\left(t_c\right)\) in a stralght line (Flg. 11.1), whose equation is

\(
\frac{t_F-32}{180}=\frac{t_C}{100} \dots(11.1)
\)

Previous Topic

Back to Lesson

Next Topic