Why is mercury in a thermometer How much mercury is in a thermometer

Reasons to use mercury as a thermometer:

Mercury has high cohesion and does not infiltrate glass.

Mercury is denser than alcohol or kerosene in the same volume.

The inertia is large, and it can be locked after leaving the body.

Specific heat capacity of mercury.

It is very small and has good thermal conductivity, which allows the mercury to change in volume in the capillary due to changes in body temperature.

The use of mercury in thermometers is not to reduce endothermy in thermometers: the specific heat capacity of mercury is compared.

Calculations show that the same volume of mercury, alcohol and kerosene absorb nearly equal heat when it rises by 1 degree Celsius.

Compared with general thermometers, thermometers have two special requirements: one is to be accurate.

Celsius, the second is to be able to leave the human body reading.

For this reason, the thermometer is constructed with "a very thin neck", but at the same time, it is necessary.

Mercury must be used. This is due to the large cohesion of mercury, which does not infiltrate the glass and can shrink during contraction.

Disconnect at the notch, thus achieving a reading out of the body. At the same time, mercury is denser and more homogeneous.

The inertia of the accumulated alcohol or kerosene is large, and it ensures that it can be thrown back into the glass bubble before use.

Reuse.

The fluctuation range of body temperature is small, and the volume of mercury is just affected by temperature, which is conducive to accurate measurement of body temperature.

How much mercury is in the thermometer

A standard mercury thermometer contains very little mercury, about two grams. Now the use of mercury thermometers is basically not allowed in foreign countries, because the harm is very great, in case the family uses the mercury thermometer, the thermometer falls to the ground, and the mercury will leak out. Although the amount of mercury in a mercury thermometer is not enough to cause much harm to the human body, it is still necessary to pay attention to the fact that it must not be wiped simply with a rag or paper towel, otherwise it will accelerate the diffusion of mercury vapor.

And it is best to hand over the collected mercury to the environmental protection department or chemical institute for proper disposal.

The principle of a mercury thermometer:

The working substance of the mercury thermometer is mercury, the lower part of the mercury thermometer is close to the neck of the vacuole is a very narrow curved neck, when measuring the body temperature, the mercury in the vacuole, the heated volume expands, the mercury can rise from the neck part to a certain position in the tube, when the thermal equilibrium with the body temperature is reached, the mercury column is constant. When the thermometer leaves the human body, the outside temperature is low, and the volume of mercury shrinks when it is cold, and it is disconnected in the narrow curved neck, so that the part of the mercury that has risen into the tube cannot be returned, and the height of the mercury column when it is in contact with the human body is still maintained.

In addition to mercury thermometers, there are several types of thermometers:

1. Electronic thermometer: It is composed of temperature sensor, liquid crystal display, button button battery, special integrated circuit and other electronic components. It can quickly and accurately measure the body temperature of the human body, and has the advantages of convenient reading, short measurement time, high measurement accuracy and memorization value.

2. Ear thermometer: It is the use of infrared spectrum emitted by the detection of the eardrum to determine the body temperature, according to the theory of blackbody radiation, the infrared spectrum produced by objects at different temperatures is also different, the use of accurate temperature difference stack infrared detector, and then the microcomputer converts the reading and appears.

3. Forehead thermometer: It is the situation of the reflection of the ant back by infrared irradiation on the surface of the forehead and the corresponding table of spectral temperature, so as to obtain the accurate temperature value.