Who doesn't want to be a good student, but if you want to be a really good student, the first thing is to study hard, that is, to dare to endure hardships, cherish time and study tirelessly. Establish confidence, firmly believe that you can learn any course well, firmly believe in the "law of conservation of energy transformation", and firmly believe that you should get several times if you pay a few times. Regarding this article, please see the following famous physical enlightenment:
I never believe in any innate or acquired talent, and I can succeed without firm and long-term efforts. -Dickens (English writer)
The main reason why some people can go far beyond others is not so much genius as his indomitable spirit of concentrating on his studies and not giving up until he reaches his goal. -Dalton (British chemist)
The fastest and slowest, longest and shortest, most common and most precious, most easily overlooked and most regrettable thing in the world is time. -Gorky (Soviet writer)
The first point mentioned above should be said to be the problem of learning attitude and thinking method. The second is to understand that there are eight links in learning as a student: making a plan → previewing before class → paying attention to class → reviewing in time → working independently → solving problems → systematically summarizing → studying after class. The most important thing here is: concentrate in class → review in time → work independently → solve problems → summarize systematically. In the above eight links, there are many learning methods. According to the characteristics of physics and how to learn physics well, this paper puts forward several specific learning methods.
(1) Sanji. (that is, the basic concepts should be clear, the basic laws should be familiar, and the basic methods should be skilled. ) about the basic concept, give an example. For example, speed represents the distance traveled by an object in a unit time: v = s/t, and for the basic law, for example, the formula for calculating the average speed is also v = s/t, which is applicable to any situation, for example, the speed of a 100-meter athlete is 10m/s when he passes half the distance, and the speed when he reaches the finish line is 8m/s. What is the average speed of this athlete in the 100 meter race? According to the law of average speed, the average speed is equal to V =100/12.5 = 8m/s. Let's talk about the basic method first. When learning junior high school physics problems, sometimes we should pay attention to the choice of objects. For example, when solving problems with ohm's law, it is necessary to make clear whether ohm's law applies to the whole circuit, that is, the whole circuit, or to a certain resistor, that is, a single resistor.
(2) Do the problem independently. Do some problems independently with good quality and quantity (meaning not relying on others). There must be a certain number of topics, not too few, but also a certain quality, that is to say, there must be some difficulty. Anyone who studies mathematics and physics can't learn this level well. Solving problems independently may sometimes be slow, sometimes you have to take detours, and sometimes you can't even solve them, but these are normal and the only way for any beginner to succeed.
(3) Physical process. To clarify the physical process, there must be hidden dangers in solving problems if the physical process is not clear. No matter how difficult the topic is, try to draw as much as possible, some can draw sketches, and some need to draw accurate pictures, using compasses, triangles, protractors and so on. To represent geometric relationships. Drawing can turn abstract thinking into image thinking and master physical process more accurately. With this diagram, we can make state analysis and dynamic analysis. State analysis is fixed, dead and discontinuous, while dynamic analysis is alive and continuous, especially when solving circuit problems. Without drawing a circuit diagram, it is difficult to know whether the resistors are connected in series or in parallel.
(4) attending classes. Listen carefully in class and don't think or think as little as possible. Don't be self-righteous, learn from the teacher modestly. Don't give up listening just because the teacher speaks simply. If this happens, it can be regarded as review and consolidation. Try to be consistent and synchronized with the teacher, and you can't do it yourself, otherwise it will be self-study. After getting started, with a certain foundation, you are allowed to have your own activity space, that is, you are allowed to have something of your own. The more you learn, the more things you have.
(5) notebook. Class is mainly based on listening, and there are notebooks, and some things should be written down. Knowledge structure, good problem-solving methods, good examples, places you don't understand, etc. Should be recorded. After class, you should organize your notes. On the one hand, you should "digest" and on the other hand, you should supplement your notes. Notebook is not only to remember what the teacher said in class, but also to make some reading notes. Good problems found in homework and good solutions should also be recorded in a notebook, which is what students often call a "good problem book". Hard-won notebooks should be numbered, studied later and kept for life.
(6) learning materials. Learning materials should be well preserved, classified and marked. The classification of learning materials includes exercises, papers, experimental reports and so on. Marking refers to, for example, marking exercises. General questions are not marked. Good questions, valuable questions and error-prone questions are marked differently for future reading. Marking can save a lot of time.
(7) time. Time is precious. Without time, there is no time to do anything, so we should pay attention to making full use of time, which is a very superb art. For example, we can save time by "recalling" learning methods. Before going to bed, waiting for the bus, walking on the road, etc. We can recall the lessons of the day section by section, so that we can learn them again and again and achieve the goal of strengthening. Some physics problems are more difficult, and some problems may be solved on foot. People who study physics often have several problems in their minds that they can't do and won't forget. I don't know when they will make a breakthrough and find the answer to the question.
(8) learn from others. We should learn from others, from our classmates, from people around us and see how others learn. We should often have "academic" exchanges with them, teach each other, learn from each other and improve together. We must never be self-righteous. Cann't be conservative Tell others if you have a good method, so that others will tell you that you have a good method. You should have some good friends in your study.
(9) Knowledge structure. We should attach importance to the knowledge structure, master it systematically, and systematize scattered knowledge. From the whole knowledge structure of physics to the knowledge structure of mechanics, even to chapters.
(10) Mathematics. The calculation of physics depends on mathematics, which is too important for learning physics. Physics is difficult to do without mathematics as a calculation tool. In the physics department of the university, mathematics and physics are equally important. To learn mathematics well, we must make good use of this powerful tool.
(1 1) Sports activities. Healthy body is the guarantee of good study, and vigorous energy is the guarantee of high efficiency in study. You should always take part in sports activities, know one or two kinds of exercise methods, take part in sports activities all your life, and do sports activities continuously. Just because you are interested in fishing for three days and drying the net for two days, it will not do much good to your health. Consciously exercise. To ensure adequate sleep, it is not advisable to increase study time by reducing sleep time. You can't get some good grades at the expense of overdraft health, you can't talk about the so-called "sprint" and "struggle" at every turn, and you should pay attention to the regularity in your study, that is to say, you should always work hard and don't engage in surprise attacks.
The above has briefly talked about some learning methods. More specific and effective learning methods need to be explored and summarized by themselves in the learning process, and others' methods need to be tested by themselves before they can become their own things. Explain common phenomena in life with physical knowledge; Explain some common practices in life from the perspective of physics.
Example 1. In the process of cooking in the kitchen, the wrong statement about physical knowledge is:
A. The surface of the kitchen knife is smooth, which can reduce the friction when cutting vegetables.
B. The blade of the kitchen knife is very sharp, which will increase the pressure when cutting vegetables.
C. The knowledge that an egg breaks at the edge of a bowl is that the forces between objects are mutual.
D. The range hood uses the principle that the faster the gas velocity is, the smaller the air pressure is to clean the oil fume.
Example 2. Beef has high nutritional value and delicious taste, and is deeply loved by people. During the processing and storage of beef, the endothermic state changes as follows:
A white gas discharged by the pressure limiting valve when the pressure cooker cooks beef.
B. Thaw the frozen beef taken out of the refrigerator with cold water.
C. The beef has just been taken out of the refrigerator, and a layer of "frost" will be hung on the surface after a while.
D. When beef is cooked in a pot in winter, "breath" will be formed on the window.
The physical knowledge involved in the above problems, from kitchen cooking, household appliances to manned spacecraft, can be explained by the physical knowledge we learned in junior high school. Knowledge of reference, force balance, friction and pressure; Thermal knowledge such as melting, liquefaction and sublimation; Short circuit, electric heating and other knowledge. And they are all phenomena that we come into contact with or pay close attention to in our daily life. Answering the above questions can not only deepen the understanding and application of physical concepts and laws, but also make students more familiar with and love life and improve their comprehensive ability. In view of the problems that need to be solved urgently in life, face up to difficulties, try to use what you have learned to design solutions, explain the solution process and show the solution results. If we can compare and evaluate the above problems, the effect will be better.
Example 1. If you work in an anti-counterfeiting office, the following measures to distinguish authenticity are reliable:
A. The best way to judge whether vendors have crushed coal gangue into high-quality coal is to detect calorific value.
B. The best way to judge whether liquor is blended with industrial alcohol is to measure the quality.
C. To judge whether an egg has expired, it can be put into high-concentration salt water for detection.
The best way to judge whether a bracelet or ring is made of pure silver is to measure the density.
Schematic diagram of automatic air switch.
A. The dotted boxes A and B are simple electromagnets with the same function.
B.A and B electromagnets are connected in parallel.
C. When the current is too large, the electromagnet A works, the lock hook is pushed away, and the main contact is disconnected.
D. When the voltage is too low, the magnetism of electromagnet B is weakened, the lock hook is disengaged, and the main contact is disconnected.
Example 3. When Mr. Wang went to turn off the main switch of the room after class, he found that the turntable of the electric energy meter was slowly turning, and the words 2500R/kWh were marked on the dial of the electric energy meter. He estimated with his watch that the dial of the watt-hour meter turned 5R in 2 minutes, so it consumed _ _ _ _ _ _ _ _ _ J power in 2 minutes. After inspection, it is found that there are still 20 computer monitors of the same model in the original computer room in standby state. Then the standby power of a computer monitor is about _ _ _ _ _ _ _ _ _ W, and the enlightenment of this topic to power saving is _ _ _ _ _ _ _ _ _ _ _.
The above topics are not only connected with social reality, but also full of life breath, which is a rare good material for the senior high school entrance examination proposition. Distinguishing between true and false is a basic skill to deal with physical or social problems, which all students should master. Example 1 highlights the concepts of calorific value, mass and density; The air switch shown in Example 2 is an industrial device. In Example 3, the first two spaces are calculated by electrical knowledge, and the last question is even more thought-provoking. This is related to the concept of "saving society" advocated by us, and it also embodies quality education. When an object is out of focus, it becomes an inverted real image on the other side of the convex lens. There are three kinds of real images: reduction, equal division and enlargement. The smaller the object distance, the larger the image distance and the larger the real image. The object is placed in focus and becomes an upright magnified virtual image on the same side of the convex lens. The greater the object distance, the greater the image distance and the greater the virtual image.
In optics, an image gathered by actual light, called a real image, can be accepted by the light curtain; On the contrary, it is called a virtual image, which can only be felt with the eyes. Experienced physics teachers, when talking about the difference between real images and virtual images, often mention such a distinction method: "Real images are upside down, and virtual images are upright." The so-called "positive" and "negative" are of course relative to the original. So the three virtual images formed by plane mirror, convex mirror and concave lens are all positive; The real image formed by concave mirror and convex lens, and the real image formed by pinhole imaging are all inverted without exception. Of course, concave mirror and convex lens can also become virtual images, and the two virtual images they form are also upright.
So is the image of the human eye a real image or a virtual image? We know that the structure of the human eye is equivalent to a convex lens, so the image formed by external objects on the retina must be a real image. According to the above rule of thumb, it seems that the object image on the retina should be inverted. But anything we usually see is obviously upright. This problem, which conflicts with the rule of experience, actually involves the regulation of cerebral cortex and the influence of life experience.
When the distance between the object and the convex lens is greater than the focal length of the lens, the object becomes an inverted image. When an object approaches the lens from a distance, the image becomes larger and the distance from the image to the lens becomes larger. When the distance between the object and the lens is less than the focal length, the object becomes an enlarged image. This image is not the convergence point of the actual refracted light, but the intersection point of their opposite extension lines, which can not be received by the light screen and is a virtual image. It can be compared to a virtual image formed by a flat mirror (the light curtain can't receive it and can only see it with the eyes).
When the distance between the object and the lens is greater than the focal length, the object becomes an inverted image. This image is formed by the light from the candle converging on the convex lens, which is the convergence point of the actual light and can be accepted by the light curtain. This is a real image. When the distance between the object and the lens is less than the focal length, the object becomes an upright virtual image.
The difference between concave lens and convex lens
I. Different structures
A convex lens is composed of a transparent mirror body, and its two surfaces are ground into convex spherical surfaces (the middle of the two tips is thick).
A concave lens consists of a transparent mirror body with concave spherical surfaces on both sides (thick at both ends and thin in the middle).
2. Different effects on light
A convex lens mainly focuses light.
Concave lenses mainly diverge light.
3. Different imaging characteristics
The convex lens refracts, and the image can be positive or negative; Virtual and real; Expansion and contraction. Play the role of spotlight
A concave lens is a refractive image, which can only be reduced to an upright image. Astigmatic lenses (including convex lenses) are instruments that transmit light and form images by folding the light. Light obeys the law of refraction.
The convex lens can be an inverted enlarged, equal-sized and reduced real image, or an upright enlarged virtual image. Parallel light can converge on the focal point, and the light emitted from the focal point can also be refracted into parallel light.
The convex mirror can only form a vertical and reduced virtual image, which is mainly used to expand the field of vision.
Convex lens imaging rule table
The distance from the object to the lens V of the positive image and the negative image of the large image and the small image of the U image is an application example.
U & gt2f, Zoom out and Reverse Real Image 2f>v>f Camera
U=2f, which is equal to the inverted real image v=2f of focal length measurement.
2f>u> Enlarge the inverted real image v & gt2f projector, slide projector, projector.
U=f No parallel light source and no searchlight.
U< magnifies an upright virtual image without a magnifying glass.
-Image memory formula-
One focal length is divided into virtual reality (one focal length is used for virtual reality imaging).
Dichotomy size (imaging size with twice focal length respectively)
You go in and I go out, and you are big and I am small (before the object moves, just like after the object moves, the image distance is small)
Concave matching convex matching concave (concave lens and convex mirror are divergent, concave mirror and convex lens are convergent)
In order to study various conjectures, people often experiment with optical bench.
Candles, convex lenses and light curtains should be kept in a straight line as far as possible.
(3) Convex lens imaging also satisfies1/v+1/u =1/f.
Using the special light of the lens as the imaging optical path of the lens;
(1), the object exceeds the focal length by 2 times.
(2) The object is between 2 times focal length and 1 times focal length.
(3) The object is in focus.
(4), concave lens imaging optical path
The experimental study on the imaging law of convex lens is as follows: when the object distance is within a focal length, an upright and enlarged virtual image is obtained; When the focal length is between 1-2 times, the inverted magnified real image is obtained; Beyond the double focal length, the real image is reversed and reduced.
This is a table to prove this rule. In fact, lens imaging satisfies the lens imaging formula:
1/u (object distance)+1/v (image distance) = 1/f (lens focal length)
The camera adopts the imaging law of convex lens.
The lens is a convex lens, the scene to be shot is an object, and the film is a screen.
The light shining on the object is diffusely reflected and imaged on the final film through the convex lens.
When the film is coated with photosensitive substances, chemical changes will occur after exposure, and the image of the object will be recorded on the film.