Why doesn t the mercury column of a thermometer drop automatically?

Hello, this is how the thermometer works.

Thermometers are also known as "medical thermometers". The working substance of the thermometer is mercury. Its vacuole volume is much larger than that of the thin tube above.

Due to the influence of body temperature, the mercury in the bubble produces a slight change, and the expansion of the mercury volume makes the length of the mercury column in the tube change significantly. The change in human body temperature is generally between 35 and 42, so the scale of the thermometer is usually 35 to 42, and the range of each degree is divided into 10 parts, so the thermometer can be accurate to 1 10 degrees. The lower part of the thermometer near the vacuole neck 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 mercury shrinks in volume 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.

It should be the truth that the bottle is tight, the mouth at the lower end of the thermometer is quite small, and there is a clever backstop design, after the temperature rises, the mercury capsule below can pass through the mercury column smoothly, and the mercury column must have a certain pressure to pass through the port with a backstop design after the temperature drops.

This design is mainly for easy viewing, so that the thermometer does not start to drop after being taken out of the mouth!

The thermometer has a deliberately narrow opening above the mercury pack that is much thinner than the other mercury columns. When the temperature rises and the volume of mercury expands, the mercury will be pushed out of the narrow position due to the high pressure inside the mercury bag, so that the displayed temperature can be seen on it.

When the temperature drops, without this slit design, the mercury volume shrinks and shrinks back into the mercury pack under the action of internal tension. But due to the location of the narrow mouth is very thin.

When the mercury shrinks, due to the greater tension between the mercury bag and the upper mercury column, the mercury column will be disconnected from the narrow mouth first, and the mercury shrinkage at the narrow mouth will make the mercury bag, and the mercury column above the narrow mouth will remain in its original position.

Creation: The first thermometer was invented by Galileo in the 16th century. But it wasn't until 300 years later that an easy-to-use, reliable thermometer was designed. Mercury is stored inside the mercury ball at the end.

When mercury is heated, it expands, rising along a very narrow glass tube. Therefore, a small change in body temperature can cause a large increase in mercury in the glass tube. After taking your temperature, shake the thermometer vigorously to return the mercury to the ball.

This is due to the special design of the thermometer.

Between the capillary glass tube and the glass bubble in the middle of the thermometer, there is a particularly small place called a neck, and it is very difficult for mercury to pass through. When the thermometer is heated, the mercury in the glass bubble expands, squeezes through the neck, enters the capillary glass tube, and then the temperature can be displayed. When cold, the mercury in the glass bubble shrinks in volume and shrinks downward.

However, the mercury that has entered the capillary glass tube cannot pass through the neck, so it can only stop in the original place. Therefore, the thermometer should be shaken before use, the purpose is to shake the mercury down.

Why is the thermometer designed this way? When you take your temperature, you need to take it out from under your armpit to take it out. If it is a general thermometer, after taking it out and exposing it to the air, the indicator will change, which is not necessarily equal to your body temperature.

In this way, the body temperature is not accurate. It is designed to have a necked face, and it will not change after taking it out, which is more accurate.

Because the various organs of infants and young children are still in the development stage, they may get sick if they do not pay attention, the more common symptoms are cold, fever, cough, etc., when the baby has a cold and fever, it is generally recommended to prepare a thermometer at home, which can measure the baby's body temperature at any time, only a slight fever, you can temporarily do not need to take medicine, and carry out physical cooling, so can the thermometer put the mercury down in the water?

Generally speaking, the mercury thermometer can not lower the mercury when placed in the water, first of all, the mercury is only composed of a graduated vacuum capillary, and the inside of the terminal ball is filled with mercury, when the temperature is tested, the mercury will expand because of the heat, and continue to rise along the capillaries, in order to detect the accurate temperature, but the mercury column needs to be shaken to come down, and it has no effect to be placed directly in the water.

At the same time, the thermometer can be placed in cold or warm water, not directly in hot water, because the mercury thermometer has a certain scale identification, if it exceeds this maximum scale, it will occur, and the mercury thermometer contains a certain amount of mercury, and the thermometer may cause mercury poisoning after it is broken, so we need to be extra careful when cleaning up the broken thermometer, and you can't take the thermometer to the child at will.

Generally, the inner diameter of the glass tube of the thermometer is the same size; However, the inner diameter of the glass tube of the thermometer is not the same thickness, and the place where the glass tube and the mercury ball meet is made very thin (neck shrinkage). When the thermometer is placed in your mouth, the mercury in the mercury ball expands by the heat, and it squeezes through this narrow opening. However, when the thermometer is removed from your mouth, the mercury is cold and immediately shrinks.

Due to the narrow inner diameter of this opening, as a result of shrinkage, the mercury at both ends is separated. This narrow inner diameter has a great friction force against the mercury, which prevents the mercury column from descending. Therefore, only after a few vigorous shakes will the mercury column return to the glass ball.

Thermometers must do this. Otherwise, when the thermometer is taken out of your mouth, the mercury will immediately shrink and drop when it hits the cold air outside, and you will not know your correct body temperature.

Refer to the pure staring test. The mercury column has a narrow position to lock in the mercury that has risen out. This will allow us to read the readings. Therefore, it can be said that the thermometer only rises and does not fall. To get the mercury pillar back, you have to shake him vigorously to bring the mercury pillar back to its lower position.

Because there is a recess in the sphere under the thermometer. You can fix the scale of the measure. As long as you shake it off. It will change back to 0 degrees. You can start all over again! When you are studying science in Form 4. Thermal"..There will be a teaching frame!

Reference: Own knowledge

Reason: 1. It may be that the mercury column has been thrown below the scale mark, and you have not found it yourself.

2. Generally, it is not easy to shake it by hand, and it is not correct to say it, it leads to an error in the body temperature measurement. You may wish to rub alcohol on the mercury ball and shake it again.

3. If you can't shake it off, it means it's broken, don't shake it. Maybe the thermometer is really broken and useless.

In the process of using a mercury thermometer, it may happen that the mercury thermometer cannot shake off the mercury. This doesn't happen very often. And if it does, you can do it:

1. Wipe the end of the mercury column with alcohol, or soak the end of the mercury column with a small amount of alcohol, wait for 1-2 minutes, and the mercury column will drop to the normal position.

2. Put it in ice water or alcohol, and the mercury will run down after a while.

It should be noted that when you take it, do not hold the thermometer tube with your hands, it is best to hold the upper end of the glass side, so that there will be few errors in the measured body temperature. After use, the thermometer should be "returned to the table" so that the mercury that has risen into the tube can be returned to the vacuole; If the mercury is not lowered back into the vacuole for a long time, the mercury is likely to condense and never go back, and it will be broken.