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Temperature and Thermometer
Calibration of thermometer
-determining the Steam Point
- The bulb of the uncalibrated thermometer is placed in the steam above a boiling water.
- The mercury level is marked. This is taken as the steam point and it’s arbitrary given as 100oC.
Notes: Instead of placing in the boiling water, the thermometer is placed in the steam above the boiling water.
Example 1
The lengths of mercury thread in a mercury thermometer are
10 mm when the bulb is in melting ice;
130 mm when the bulb is in the steam above boiling water and 40 mm when the bulb is in a liquid A.
What is the temperature of liquid A?
Answer:
l0 = 10mm
l100 = 130mm
lθ = 40mm
\begin{gathered}
T = \frac{{l_\theta - l_0 }}
{{l_{100} - l_0 }} \times 100^o C \hfill \\
T = \frac{{40 - 10}}
{{130 - 10}} \times 100^o C \hfill \\
T = \frac{{30}}
{{120}} \times 100^o C \hfill \\
T = 25^o C \hfill \\
\end{gathered}
Sensitivity of Thermometer
The sensitivity of a thermometer can be increased by
- Using a thermometer with a smaller bulb – A smaller bulb contains less mercury and hence absorbs heat in shorter time.
- A glass bulb with thinner wall – Heat can be transferred to the bulb easily.
- Capillary with narrow bore – produces a greater change in the length of the mercury column.
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