Temperature and Thermometer

Card 1: Calibration of thermometer-determining the Ice Point

Calibration of thermometer
-determining the Ice Point

  • The bulb of the uncalibrated thermometer is placed in the ice.
  • The mercury level is marked. This is the taken as the ice point and it is arbitrarily given as 0oC.
Card 2: Calibration of thermometer-determining the Steam Point

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.

Card 3: Calibration of thermometer-Measuring the temperature.

Calibration of thermometer-Measuring the temperature.

After marking the ice point (0oC) and steam point (100oC), the temperature of a substance can be determined by the formula:

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} 
            

 

Card 4: Sensitivity of Thermometer

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.
Card 5: Increases the Accuracy of Thermometer

Accuracy of Thermometer

To increase the accuracy of a thermometer, the diameter of the capillary tube of the thermometer must be constant throughout.

Card 6: Advantages of Using Mercury as the Liquid in a Thermometer

Advantages of Using Mercury in a Thermometer.

  • It doesn’t wet the side of the tube.
  • It makes a thread which can be seen easily.
  • It expand uniformly when heated
  • It can conduct heat well. Therefore it reponses quickly to temperature changes
Card 7: Disadvantages of Using Mercury as the Liquid in a Thermometer

Disadvantages of Using Mercury

  • It freezes at -39oC. Therefore it is not suitable for measuring temperature lower than -39oC.
  • It is poisonous
  • It is expensive
Card 8: Advantages of Using Alcohol as the Liquid in a Thermometer

Advantages of Using Alcohol

  • It freezes at -115oC. Therefore it is suitable for low temperature, including the Artic and Antarctic region.
  • It expands greater than mercury.
Card 9: Disadvantages of Using Alcohol as the Liquid in a Thermometer

Disadvantages of Using Alcohol

  • It is transparent and difficult to be seen. It has to be coloured in order to be seen easily.
  • It always clings to the sides of the tube.
  • The thread has tendency to break.
Card 10: What is absolute temperature?

Absolute Temperature

Absolute temperature is the temperature measured in Kelvin scale, which it is a temperature reading made relative to absolute zero.

Card 11: What is Absolute Zero?

Absolute Zero

Absolute zero is the temperature where thermal energy is at minimum. It is 0 on the Kelvin scale and -273 on the Celsius scale.

 

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