Name: The Most Important Instrument
Uploaded: 2019-07-19
Duration: 7 min 34 s
Description: The more modern thermometer was invented in 1709 by Daniel Fahrenheit. In this video, we will learn about thermometers and how it is invented and used.

Question

Describe the construction of a laboratory thermometer. Give two precautions to be taken while reading a laboratory thermometer.

Accepted Answer

Laboratory thermometers are used to measure the temperature in school and other laboratories for scientific research. They are also used in the industry as they can measure temperatures higher than what clinical thermometers can record. The following diagram represents a laboratory thermometer.

A laboratory thermometer consists of a very fine capillary tube, protected by a thick glass tube called the stem of the thermometer. The lower end of the capillary tube is converted into a glass bulb filled with mercury and the upper end of this tube is sealed. The stem is marked in $° C$ or $° F$ . The commonly used laboratory thermometers have a range from $- 10 ° C$ to $110^{°} C$ . The stem and the bulb of a lab thermometer are longer when compared to that of a clinical thermometer and there is no kink in the lab thermometer. When the thermometer is in contact with a hot body, the mercury in the capillary tube expands and rises up. When the thermometer is in contact with a cold body, the mercury in the capillary tube contracts and falls down. It is because of the effect of heat that causes expansion or contraction. A laboratory thermometer cannot be used to measure the human body temperature. This is because as soon as we take out the bulb of the laboratory thermometer from our mouth, the level of mercury in its tube will start falling quickly. This will give a wrong value of the body temperature.

The following are the precautions to be taken while using a laboratory thermometer:

1) The laboratory thermometer should be held vertically while measuring temperature. It should not be tilted.

2) The thermometer bulb should not touch the sides or bottom of the container in which the substance is taken.

3) The thermometer bulb should be surrounded from all sides by the substance whose temperature is to be measured.

4) Read the thermometer by keeping the level of mercury along the line of sight.

Describe the construction of a laboratory thermometer. Give two precautions to be taken while reading a laboratory thermometer.

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