Experimental technology experiment and instrument i Zhang Arong, Yutian Town, Yutian County, Hebei Province (064100) Physics Bulletin Edition, Junior High School Physics, Volume 2, page 21-7, there is a demonstration experiment of “energy can be increased when the air is compressedâ€, which is compressed by air. The ignition device is completed. The principle of the experiment is: the piston compresses the air to do work, so that the internal energy of the air increases, the temperature rises, and the ignition point of the cotton is reached, so that the cotton is ignited and burned. There must be two conditions for the burning of cotton: first, to reach the point of ignition of cotton; second, to have sufficient oxygen.
In this experiment, ordinary cotton can not be seen in the burning phenomenon. With cotton immersed in ether, only white smoke is emitted in the cylinder, and the burning phenomenon of cotton is not seen, and the experimental results are not satisfactory. I have been engaged in physics teaching for many years. After repeated exploration of the demonstration experiment, I feel that there are two kinds of experiments: (1) using nitrocellulose. Put a little nitrocellulose into the tube, press the piston down quickly, and the nitrocellulose will burn immediately, giving off a dazzling spark, and the experimental effect is very obvious.
The production process of nitrocellulose is as follows: 98% concentrated sulfuric acid and 5 ml concentrated nitric acid are placed in a beaker, then put on cotton wool, stir with a glass rod, so that the absorbent cotton is completely saturated, and after half an hour, wash with water (do not start cleaning) Use your hand to prevent the acid from hurting your hands) until the water is not acidic. After squeezing out the water, let it soak in alcohol, remove it, squeeze the alcohol, and then dry it to make nitrocellulose. Biting should be taken during the experiment: take a small amount of nitrocellulose into the tube, and too much will cause the glass tube to be fried. (2) The simplest method of this experiment is to put a little ordinary cotton in the tube, and then put a match head The nitrate part (chemical composition: potassium chlorate, manganese dioxide, and antimony trisulfide) is scraped off, ground into a powder, placed in a human barrel, and quickly pressed down the piston. The cotton immediately ignites and ignites a spark. The experiment should be completed; take a small amount of ordinary cotton into the tube, and let the cotton in the bulky state, a match head powder can be placed in the tube, too much will cause the glass tube to burst.
裨æ‘f-foot over the seat Sé Wang Changhong Henan Province Gushi County Shifo High School (465200) Vernier caliper is an important tool for measuring length in high school physics experiments, can be used to measure the length of the object, the inner diameter, outer diameter of the container and Depth and so on. For the structure and principle, the author has carried out another design. Now take the 10 degree vernier caliper as an example to introduce.
Principle: The minimum graduation of the vernier caliper is 1mm, the vernier has 10 small halving scales, and their total length is 11mm, so each index of the vernier caliper is 1.1mm, which is 0.1mm more than the minimum division of the main ruler. That is, when the vernier scale coincides with the zero-scale line of the main ruler, the last gradation line of the vernier scale coincides with the 11mm mark line of the main ruler (for example), and if the vernier scale moves 0.1mm to the right, the 1 mark line to the right of the vernier ruler and the main The ruler of the ruler 10mm is aligned, that is, the length of the object to be measured is 0.1mm; if the ruler moves 0.2mm to the right, the 2nd mark line on the right side of the ruler coincides with the 9mm mark line of the main ruler, that is, the length of the object to be measured is. 1mmx2 = 0.2mm; and so on, total reading = millimeter integer + millimeter decimal. In this vernier caliper, the tick mark pitch of the vernier scale is larger than that in the textbook, and it is easy to observe the scale of the vernier scale tick and the main ruler, and the reading is more accurate and convenient.
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