Laboratory Thermometer
How do we measure the temperature of other objects? For this purpose, there are other thermometers. One such thermometer is known as the laboratory thermometer. The teacher will show you this thermometer. Look at it carefully and note the highest and the lowest temperature it can measure. The range of a laboratory thermometer is generally from –10°C to 110°C (Fig. 4.4).
Fig. 4.4 A laboratory thermometer
Also, as you did in the case of the clinical thermometer, find out how much a small division on this thermometer reads. You would need this information to read the thermometer correctly.
Let us now learn how this thermometer is used.
Activity 4.4:
Take some tap water in a beaker or a mug. Dip the thermometer in water so that the bulb is immersed in water but does not touch the bottom or the sides of the container. Hold the thermometer vertically (Fig. 4.5). Observe the movement of mercury in the thermometer. Wait till the mercury thread becomes steady.
In addition to the precautions to be taken while reading a clinical thermometer, the laboratory thermometer
should be kept upright not tilted. (Fig. 4.5)
the bulb should be surrounded from all sides by the substance of which the temperature is to be measured. The bulb should not touch the surface of the container. |
Fig. 4.5 Measuring temperature of the water with a laboratory thermometer
Note the reading. This is the temperature of water at that time.
Compare the temperature of water recorded by each student in the class.
Are there any variations in the readings? Discuss the possible reasons.
Let us try to answer this question.
Activity 4.5:
Take some hot water in a beaker or a mug. Dip the thermometer in water. Wait till the mercury thread becomes steady and note the temperature. Now take out the thermometer from the water. Observe carefully what happens now. Do you notice that as soon as you take the thermometer out of the water, the level of mercury begins to fall? This means that the temperature must be read while the thermometer is in water.
You may recall that while taking your own temperature, you have to take the thermometer out of your mouth to note the reading. Can you then use the laboratory thermometer to measure your body temperature? Obviously, it is not convenient to use the laboratory thermometer for this purpose.
Why does the mercury not fall or rise in a clinical thermometer when taken out of the mouth?
Observe a clinical thermometer again. Do you see a kink near the bulb (Fig. 4.6)?
What is the use of the kink? It prevents mercury levels from falling on their own.