Ways to improve the ability of junior high school students to solve physics problems
1 Emphasis on the application of mathematical methods Applied physics problems Compared with physical concept problems, the application questions are closer to real life, although the problems are not long, but the quantitative relationship is somewhat scattered and hidden, and the applied mathematical methods are more flexible, therefore, facing some non- Formal materials, many students feel awkward, do not know where to start, the fear of applying physics questions, always feels difficult, leading to the market, often difficult to read the title, and finally only give up.
In response to this phenomenon, teachers should analyze some typical application physics problems and find some clever solutions to help students master mathematical operations.
Example 1 An electric hot drinker has two electric heating wires of AB, and the electric heating wire is connected in series on the power supply, and the water in the drinking fountain is heated to boiling in 16 minutes. If A is separately connected to the same power source, the initial temperature and quality are the same. It takes 6 minutes for the water to heat up to boiling. If B is connected to the same power source separately, it takes a long time (excluding heat loss) to heat the water with the same initial temperature and the same quality. This question focuses on the students' mathematical research.宄 physics problems, from the analysis of physical phenomena and processes, through generalization, abstraction and other means, turn physics problems into mathematical problems.
The power supply voltage is set to uAB. The two electric heating wire resistances are Ra. Rb is heated by the isothermal mass to the boiling, that is, the absorbed heat is the same (Q), and the formula is calculated by Q=ft: (1) Deformed Shen Jiangqing (959-) male, Zhejiang Huzhou, and the first teacher of Zhenyuan No. 2 Middle School.
The (2) deformation will be (3) deformation observation (4), (5), (6) on the right side, found (4) = deepen the question, change the angle of the question, cultivate students' correct thinking method, make thinking Develop in depth to the problem. It becomes: a heating wire R is connected to the power source, and can melt m kilograms of water having an initial temperature of t at T minutes. If the heating wire is folded in half and connected to the same power source, it takes a long time to boil the same water. Analyze according to the above-mentioned derivation T==+T. Similarly, if R is elongated to the original, if it is to be heated The wire is connected to the power supply whose voltage is half of the original voltage. How long does it take to boil the same water? It can be realized through the above example. The application of the physics problem is not just a physical exercise, but has been put on the actual background. mathematical method. Of course, physics is different from mathematics, mathematics has a quantitative relationship, and physics is "reasonable". When solving equations in a column equation, there must be a solution to the problem. Physics has physical laws, and physical facts and laws must be followed throughout the process. When the physical state, condition or process changes, the laws governing the physical quantity and the formula used may change, which must be reflected. At the same time, attention should be paid to the difference between the same physical quantity in different states or processes, usually at the right of the letter. Add a corner to the lower corner or add "" in the upper right corner to distinguish.
Solving the application of physical problems requires mastering problem-solving strategies, with a solid physical foundation knowledge, skilled mathematical methods, will be handy.
2 Strengthening the awareness of the questions in the process of answering questions To solve a problem, we must first understand the problem. The physical problem stems from the practice of life production. Although it can be transformed into a typical physical problem to answer, due to the diversity and complexity of objective reality, Make the background of the problem more comprehensive, which requires students to answer the practical questions.
Example 2 Do you think that in order to make the hydropower station generate electricity all year round, what are the important natural conditions that must be met in the site selection? A: a. To have ample water, it should be selected in rainy areas. b. It can't be frozen all the year round. It should not be built in cold areas. It is generally selected in the tropics and subtropics. The reservoir has high geological requirements and can withstand large pressures. d The difference between the upper and lower water levels is large... The population of the reservoir inundation area cannot be dense.
The method that teachers should use to help students review questions: reduce problems and find conditions. In the face of application questions, you should first read carefully, while reading, while thinking; repeat reading questions, pay attention to the important statements, the relationship between the data. This can simplify the problem, as in Example 1, "The same power supply, absorbing the same heat in Example 2" year-round "normal* (concealed condition).
Teaching students to understand keyword phrases. For example, a bottle can hold 1 kilogram of water and can hold 1 kilogram of alcohol (known as pK>ps). The keyword is "the same bottle, the same volume (stable condition) * that is no more than 1 kilogram of alcohol (m water > m case 3 on energy and energy use, the following statement is correct ().
A. Solar energy can only be converted into internal energy through heating equipment such as solar cookers and solar furnaces, so it belongs to secondary energy. B. China is rich in energy, so solar and nuclear energy development is not important. C. The thermonuclear reaction occurs only in the natural world under artificial conditions. D. The chemical energy of coal, oil and natural gas is ultimately derived from solar energy.
The analysis of solar energy is the primary energy source provided by nature. Like electric energy, which is converted from energy provided by nature, it is secondary energy. Although China's energy is abundant, it has a large population and a small amount of resources per capita. Therefore, it is particularly important to develop new energy sources. The reaction inside the sun is a thermonuclear reaction, which does not require artificial conditions. The chemical energy of coal, oil and natural gas ultimately comes from solar energy. Plants absorb solar energy and transform the chemical energy of plants through photosynthesis. Plants are eaten by animals and converted into chemical energy in animals. Plants and animal bodies are buried underground, and become geologically transformed into oil, natural gas, and coal. Should choose D. 3 Initially learn to build a physical model 3.1 Learn to simplify and symbolize the problem. If you have understood this problem with a practical background and can retell the problem in your own language, what you need to do now is: Try to change the way to simplify the problem in your mind, that is, teach the students to try to Turn the problem into a familiar and simple question for the student, then use the alphabetic symbol to indicate the number of questions in the question. If necessary, use some simple calculations to perform some trial calculations and use the list. +Association, conjecture, logical reasoning and other methods to find the mathematical relationship (physical formula) in the problem and the related relationship of physics knowledge. This quantitative relationship and the change of physical quantity are established by using the physical model and using the mathematical knowledge learned.
In example 4, the objects of A and B are of equal mass and the temperature is the same. The material is first put into a cup of hot water. After the heat balance, the water temperature is lowered by 8*C. The object is taken out (the quality of the water is not lost) and then the object is put into the cup. In hot water, the water temperature is reduced by 8 ° C after heat balance. It can be seen that A. A has a larger specific heat. B. B is hotter than the heat. C. Both are as big as heat. D. Unable to judge.
It is difficult to judge the final temperature of the two objects A and B. This is the difficulty of this problem. The key to the breakthrough is to symbolize the conditional letters and take the data to explain it. 1. Depending on the conditions, the heat absorbed by the mixture of water and water is the same as that before and after mixing with water. To compare their specific heat, just compare their final temperatures. 2 Set the initial temperature of A and B to 30*C; hot inference: the temperature of the end of the material is 62C, the temperature rises to 32C, and the temperature of the end of the 54C temperature rises by 24C. Conclusion: the temperature of the end of the material is 62C> the temperature of the end of the 54C. More than the potential, choose B. 3.2 to learn to draw schematics and other methods to suggest the implicit quantitative relationship. For those whose quantity relationship is not clear, according to the laws of physics, draw a simple diagram to simplify the problem, straighten out the relationship, and reveal the inner relationship.
Example 5 (1999 national competition title) Xiao Ming's experiment of 'study convex lens imaging' on the optical bench. When the relative positions of the light screen, lens and candle flame are as shown in the figure below, it can be drawn on the light screen. A clear image, from which he judged, the focal length of the convex lens he used: A. is between 10 cm and 16 cm; D. is set between 8 cm and 10 cm.
The analysis shows that the object distance u=16cm at this time is obvious, U>v is the object distance is larger than the image distance. According to the law of convex lens imaging, when the object distance u is larger than the image distance v, the object distance must be >2f; and when the object distance is >2f, there must be 2 £: 20cm>f 10cm, so the answer is D. 4 Reasonable explanation and answer physics Practical problems After answering the physics application questions solved by mathematical methods, students should be taught to return the results to the actual situation to see what kind of actual situation is reflected in the results to determine whether the answer has practical significance. reasonable. Also, check to see if your answer has run out of all the important information. Finally, don't forget to write your answer in a complete statement.
Example 6—The resistance of the DC motor line is 4 ohms. When it is connected to a 220 volt circuit for normal operation, the output power of the motor is 1 kW. What is the current through the motor?
Analyze that the motor is a machine that converts electrical energy into mechanical energy, that is, the electric motor consumes electric energy, and the output is mechanical energy. However, when the electric current passes through the electric motor wire, due to the thermal effect of the electric current, some electric energy is converted into heat energy and is dissipated, so There is P electricity = P heat + P machine. Since the current through the motor is I, uI=I2R+P solves 1=5 amps or 50 amps.
Obviously, the motor is not an electric heater. If the answer is 50, it obviously does not conform to the physical meaning, so the correct answer to the question is 5 amps.
To train students' ability to solve application problems, firstly, basic knowledge and basic skills training; to train students to gradually master the variability of physical processes, the most important is to cultivate students' modeling ability, and to transform application problems into physical processes. Basic training for extracurricular, experimental, etc.
Durable Baby Bags are becoming more and more popular as regular items for babies and parents. Whether it is a long-distance travel or a short trip, Diaper Bag provides important convenience for babies and parents. The popularity of diaper bags has caused new parents to pay more attention to infant travel, not only psychologically but also physical changes, with great significance.
Baby Bag Backpack,Durable Baby Diaper Bags,Durable Nappy Baby Bag,Durable Baby Bag
JOYBABIES PRODUCT CO.,LTD. , https://www.my-joybabies.com