Senior Two | Physics Experiment and Labor Practice Work Exhibition

　　Editor's note:

　　For the universe, human beings can be so small that they are not worth mentioning. Humans are lonely and the future is unknown. However, people can understand the world a little through physics, and can eliminate the fear of the world, which is the charm of physics. Physics is so interesting that you can sigh the insignificance of human beings in the world, but it can also make human beings feel a little bit of pride in seeing the mysteries of the world. Up to the prehistoric universe, down to the molecular atoms, physics is always with us. This is the magic of physics.

　　During the May 1st holiday, the science class of senior two conducted a unique and interesting verification experiment on optics, heat, simple harmonic motion and other knowledge learned in this semester. Teachers Liu Zaiying and Liu Baoxiang provided a variety of novel and interesting creative experiments for everyone, and gave corresponding guidance to the students. The students not only deepened their understanding of physical knowledge, but also exercised their hands-on ability, and understood the scientific research and verification spirit of "practice brings true knowledge".

　　What follows are physics experiments done by the Senior Two students.

　　liquid surface tension

　　The force acting on the surface of the liquid to reduce the surface area of ​​the liquid is called the surface tension of the liquid. The reason for it is that there is a thin layer on the surface of the liquid in contact with the gas, which is called the surface layer. The molecules in the surface layer are sparser than those in the liquid, the distance between the molecules is larger than that in the liquid, and the interaction between the molecules is expressed as tension. It's like if you want to stretch the spring apart, the spring has a tendency to contract instead. It is precisely because of this tension that some small insects can walk freely on the water without restraint.

　　When two waves of the same frequency, constant phase difference, and the same vibration direction are superimposed, the vibration in some areas is always strengthened, and the vibration in some areas is always weakened. This phenomenon is called wave interference. The resulting stable pattern is called an interference pattern.​​

　　Not only water waves will interfere, but all waves such as sound waves and electromagnetic waves can interfere as long as the above conditions are met.

　　Thin film interference experiment

　　The reflected light from the front and rear surfaces of the liquid film superimposes each other and interferes, which is also called thin-film interference. Generally speaking, the thickness of the liquid film at different positions is different, so at different positions on the film, the path difference of the reflected light from the front and rear surfaces is different. In some positions, the two waves strengthen each other after superposition, and bright stripes appear; in other positions, they weaken each other after superposition, and dark stripes appear.

　　capillary phenomenon

　　The phenomenon that the wetting liquid rises in the thin tube and the phenomenon that the non-wetting liquid descends in the thin tube is called capillary phenomenon.

　　resonance phenomenon

　　Resonance means that when the frequency of the driving force is equal to the natural frequency, the amplitude of the forced vibration of the object reaches the maximum value. These specific frequencies and wavelengths are called resonant frequencies and resonant wavelengths.

　　Physical background knowledge：

　　In the process of studying thermal phenomena, the first thing people encounter is the problem of temperature measurement.

　　Let's do the following experiment first. Put your right hand into a basin of hot water, and your left hand into a basin of cold water. After a while, put your hands into a basin of warm water at the same time. At this time, you will find that the feeling of warm water in both hands is different. The right hand feels warm and cold, and the left feels warm.

　　This experiment shows that people's senses alone cannot accurately compare the degree of cold and heat of objects, and there must be an instrument that can measure the temperature of objects.

　　At the end of the 16th century, Galileo spent a lot of effort in developing the thermometer. His goal at the time was to create an instrument that could indicate how "hot" an object was. He used the word "heat" because the word "temperature" didn't exist at the time. As early as in ancient Greece, scholars at that time knew that air had the property of expanding with heat and shrinking with cold. By 1593, Galileo had deeply studied the phenomenon of thermal expansion and contraction of gas, and used this property of gas to create the world's first gas thermometer.

　　Galileo's gas thermometer has a very simple structure: prepare a slender glass tube with a hollow spherical shape at one end and an opening at the other end, pour some colored water into the glass tube in advance, and then turn the opening of the glass tube upside down. Insert into a container of water, thus making a thermometer. When the glass ball is slightly heated, the gas in the ball expands and the water level in the glass tube decreases; conversely, when the temperature is lower, the gas in the ball contracts and the water level in the tube rises. Divide several grids on the glass tube, engrave the scale, and you can measure the temperature.

　　However, since the lower end of Galileo's thermometer is connected to the atmosphere, the water level in the glass tube is not only affected by the air temperature in the hollow sphere, but also related to the frequently changing atmospheric pressure. In this way, the temperature measured by Galileo's thermometer appears rough.

　　How can the shortcomings of Galileo's gas thermometer be overcome? Later, a student of Galileo named Ferdinand inherited and perfected this work.

　　From the fact that gas has the property of thermal expansion and contraction, Ferdinand thinks, does liquid have the phenomenon of thermal expansion and contraction? After several experiments, he affirmed his idea that liquids also have the properties of thermal expansion and contraction. Next, Ferdinand further speculated that it is possible to use the properties of liquid thermal expansion and contraction to indicate temperature like a gas? Ferdinand experimented with various liquids instead of gases. He later found that the volume of alcohol changed significantly after being heated. Finally in 1654, Ferdinand made the world's first liquid thermometer. The structure of this liquid thermometer is: pour an appropriate amount of colored alcohol into the glass ball, then slightly heat the glass ball, use alcohol vapor to drive away the air in the glass tube, and then seal the glass tube mouth at once. After the mouth of the thermometer is sealed, the influence of atmospheric pressure on temperature measurement is eliminated, so that the accuracy of temperature measurement is significantly improved.

　　However, shortly after the use of the alcohol thermometer, people found another problem: when the alcohol thermometer was used to measure the temperature of boiling water, the thermometer was blurred and could not be read at all. It turned out that the boiling point of alcohol is very low, only 78 ℃. When the temperature of the measured object reaches 78°C, the alcohol in the alcohol thermometer will boil and turn into gas, so this thermometer can only measure the temperature of objects below 78°C.

　　So what to do with a higher temperature? Later, it was found that the boiling point of mercury is very high, reaching 357 ° C, so another liquid thermometer, the mercury thermometer, came out in 1695. The mercury thermometer can measure very high temperatures, but its ability to measure low temperatures is very poor, and it will freeze when it reaches minus 39 degrees Celsius. Therefore, we usually use alcohol thermometers to measure the temperature of the cold and summer table, and its range is from minus 114 ℃ to minus 78 ℃, which is enough for measuring the daily temperature around the world.