What is the principle of thermometer?

Thermometers are made according to the principle of expansion when heated and contraction when cooled. The metal end of the thermometer is filled with mercury or alcohol, which will expand when heated, thus indicating the temperature. When you fan the thermometer with your hand, it only blows the air around the thermometer, but does not lower the temperature of mercury in the glass column, so the mercury column will not fall.

/kloc-in the 6th century, the medical school of Padua University in Italy was famous all over Europe, and Galileo, a great scientist, once taught in this university. Galileo came into contact with many doctors in this famous medical university, so he often wanted to build some instruments that were helpful to doctors. One day, Galileo held the bottom of a test tube with his hand. After a while, he inserted the upper end of the test tube into a basin of cold water and then let go of his hand. The pipe became cold and sucked up the water. Galileo held the test tube with his hand again, and the test tube gradually became hot, and the water inside went down again. Galileo marked a series of scales on the test tube and marked numbers on each scale.

The experiment was so interesting that Galileo asked all his students to do it. When each student puts his hand on the glass test tube, the water will always reach the same scale. Galileo told his students that it was because their blood always had the same heat-the same temperature. Galileo also demonstrated the experiment in a speech.

Galileo was associated with this: this experiment can actually help doctors work. When people get sick, the temperature in the blood usually rises. When a patient holds a test tube, the water in the tube will rise to a higher scale due to the increase of the patient's blood temperature, so that the doctor can know the heat of the patient's blood. So Galileo invented the first thermometer.

However, after the thermometer was made, Galileo was not satisfied with his invention, because water would freeze in cold weather. When water freezes, its volume would expand, and the ice would break the test tube. Galileo experimented with many kinds of liquids. Finally, he chose an alcohol, which won't freeze in winter and becomes a good liquid for making thermometers.

At present, thermometers that use alcohol as liquid in thermometers are still in use.

Before using the thermometer, shake it hard to make its indication return to zero.