How to Measure Resistance Yang Zhijun Correctly with Multimeter (Yangquan Yangmei Vocational Education Center 075800) Abstract: Multimeter is a multifunctional and multi-range measuring instrument, which can generally measure parameters such as current, voltage and resistance. It is an essential instrument for electronic and electrical installation, debugging and maintenance. For students majoring in electronic and electrical engineering, it is of great significance to use multimeter correctly. Based on years of teaching and practice, the author summarizes the basic method of measuring resistance with multimeter, and has achieved good teaching effect in teaching. Key words: Electronic and electrician multimeter, also known as multimeter, multimeter or multimeter, is a multi-functional, multi-range star measuring instrument. General multimeter can measure DC current, DC voltage, AC voltage, resistance, audio level, and some can also measure AC current, capacitance, inductance and some parameters of semiconductor (such as B). Multimeter has the advantages of multi-function, multi-range, easy to use, small size, easy to carry and low price. It is widely used in scientific experiments and industrial and agricultural production, and is also an essential instrument for electronic and electrical installation, debugging and maintenance. For students majoring in electronics and electrician, it is of great significance to use multimeter correctly. Based on years of teaching and practical experience, I summarized the basic method of measuring resistance with multimeter. Good teaching results have been achieved in teaching. Next, I will take the 500 multimeter as an example to explain the specific method of measuring resistance. I. Structure of Model 500 Multimeter Model 500 Multimeter consists of three main parts: meter head, measuring circuit and change-over switch. (1) ammeter It is a high-sensitivity magnetoelectric DC ammeter, and the main performance indexes of multimeter basically depend on the performance of ammeter. The sensitivity of the instrument refers to the DC current value flowing through the instrument when the pointer of the instrument deflects at full scale. The smaller the value, the higher the sensitivity of the blood glucose meter. When measuring voltage, the greater the internal resistance, the better its performance. There are four tick marks on the meter, namely: the first one (from top to bottom) is marked with R energy, and this physical phenomenon with instantaneous change is put into "slow motion" to analyze cars, wood blocks and their relationships one by one. Because the image is clear and the simulation is realistic, it is convenient for students to explain and observe and understand, so it gets twice the result with half the effort. On this basis, several other topics related to the application of inertia explanation are projected and demonstrated, and students are required to analyze and explain according to the previous description. Through intensive training, students quickly mastered the method of explaining physical phenomena with inertia. For example, atmospheric pressure, the application of hydraulic brake, the application of lever balance condition, convection phenomenon in liquid heat transfer, etc., can be simulated by projection, which can directly explain the problem and reveal the physical laws. So as to enhance the experimental nature of physics teaching. There are also some physical experiments that can be demonstrated in class, but because of the small teaching AIDS and other reasons. It is not convenient for the whole class to observe, especially the repeated demonstrations in the review stage. At this time, using projection to simulate physics experiments can strengthen the experimental nature of physics teaching. For example, "Measuring the Electric Power of Light Bulbs" is an experimental course using a variety of electrical instruments, which requires high experimental skills for students. Often because students seldom touch experimental instruments, they use various electrical instruments to measure in one class, and some students feel at a loss. Circuit connection errors often occur, and even an experimental data is not measured after a busy class. In order to reduce the difficulty of students' experiments. Let the students do the experiment smoothly according to the steps. I designed and made a slide to measure the electric power of a small light bulb and simulate the experimental process. Before class, I combined with physics experiments, demonstrated step by step, and explained the use method and experimental steps of the instrument, which saved time and effort, was intuitive and operable, and greatly accelerated the speed and accuracy of students' experiments. Third, the use of projection teaching to strengthen information feedback. Two-way communication between teaching and learning. Improve the quality of teaching. Pedagogy shows that the teaching process is actually a complete process of information transmission and control. The control process is realized by information feedback. Therefore, how to strengthen information feedback in the teaching process is also one of the important measures to improve the quality of education and teaching. For example, according to the needs of teaching objectives, part of the teaching content will be made into various types of standardized training exercises such as filling in the blanks, filling in maps, filling in forms, multiple-choice questions, judging questions and correcting wrong questions. In teaching, teachers should grasp the opportunity according to the needs of teaching, reflect it in time through projection, and let students answer orally and discuss it in writing; Some students can also write their answers on the glass board, or write their answers on the slide in front of the projector, and these answers will be reflected and commented immediately. It has large capacity, diverse questions, flexible methods and quick presentation. The timeliness and remarkable effect of feedback are beyond the reach of other teaching links. 178 for example, after Archimedes' lecture. I use a box of drawings and synthetic slides to demonstrate: ① What are the main factors that determine buoyancy when the same object is immersed in liquids with different densities? ② What are the main factors that determine the buoyancy when objects with different volumes are immersed in liquids with the same density? ③ How does the buoyancy change when the same object is immersed in the same liquid at different depths? ④ How does the buoyancy change when the object is gradually immersed in the liquid? I firmly grasp Archimedes' principle and his formula, starting from two key factors: the density of an object immersed in liquid and the volume of liquid discharged by the object. With the help of the visual image of the projection, the various situations on the blackboard are compared, compared and summarized, so as to guide students to deeply understand the connotation of Archimedes' principle and the thinking method of analyzing problems, and to make students thoroughly understand which factors are related to buoyancy. Because of the concrete image of the slide, the effect of inspiring thinking is good. Teaching practice has proved that all kinds of practice films are not only simple to make, flexible to use and timely to give feedback, but also can be summarized, classified, analogized, compared, generalized and summarized through projection according to the pertinence, contrast and comprehensiveness of knowledge. Therefore, the information exchange between teaching and learning has been strengthened. Fourth, use projection to demonstrate in kind. Enhance the experimental effect. Expand the observation field and cultivate students' observation ability. In junior high school physics teaching, teachers need to do a lot of demonstration experiments to illustrate abstract theories with concrete facts or draw physical laws from them. This is also one of the main methods for junior high school students to learn physics. However, because some experimental teaching AIDS are small or the changes are not obvious, the experiment is not convenient for the whole class to observe clearly and the expected teaching effect cannot be achieved. In this case, the effect is obviously enhanced by doing physical projection experiments. For example, in the class "Magnetic Effect of Current", Oster's experiment was shown on the lecture table in the past. Because the deflection of the small magnetic needle is not convenient for the whole class to observe and affects the teaching effect, I made the above experiment with physical projection, and directly magnified the projection of what happened on the screen. In this way, students can see clearly, thus enhancing the demonstration effect. At the same time, this novel method stimulates students' senses, arouses students' attention, and is more serious than observing objects, thus helping students to cultivate their observation ability. There are many experiments in junior high school physics demonstration experiments, such as measuring the diameter of a circle with a transparent scale and a triangular plate; The key to improve the measurement accuracy is to measure the length of small blocks with different scales and the use of scales. In a small experiment. Bending experiment of bimetal, liquid diffusion phenomenon, existence and distribution of magnetic field around magnet, etc. Can be demonstrated by physical projection. ... class =' class1' > strategy of implementing environmental education in middle school chemistry teaching Zhang Man (Taizhou No.1 Middle School, Taizhou, Zhejiang 3 18000) Abstract: Environmental education is a hot issue in education in the 2/KLOC-0 century ... Combined with teaching practice, the author expounds and analyzes the objectives, principles and ways of implementing environmental education in chemistry teaching. Keywords: environmental education approach in senior high school chemistry teaching. With the increasingly serious global environmental problems, environmental education has been paid more and more attention by governments and people all over the world. Environmental education is an education for the whole society, which has become an important means to improve the ideological and moral quality and scientific and cultural quality of the whole nation and an important part of environmental protection and education in China. Chemistry runs through the interaction between human activities and the environment, and the final solution of environmental problems depends on chemistry. Chemistry in senior high school is a subject closely related to the environment, and chemistry teaching provides basic scientific knowledge for environmental education. The implementation of environmental education in senior high school chemistry teaching conforms to China's educational situation and social needs, and is beneficial to students to cultivate good public environmental awareness, establish scientific chemistry concepts, acquire environmental scientific knowledge and solve environmental problems. Improve students' scientific literacy and comprehensive environmental quality. First, the goal of implementing environmental education in chemistry teaching 1. The overall goal of implementing environmental education in chemistry teaching. The general goal of implementing environmental education in senior high school chemistry teaching basically includes five aspects of environmental education: awareness, knowledge, attitude, skills and participation, and also includes four aspects: understanding the environment, caring for the environment, protecting the environment and improving the environment. It is embodied in five goals: (1) improving the comprehensive environmental quality; (2) Understanding the important influence of chemistry on human society and correctly understanding the relationship between chemistry and environment; Or n, indicating the resistance value. When the changeover switch is in the ohm range, read the scale line. The second line is marked with a and VA, which represent the values of AC and DC voltages and DC current. When the change-over switch is in the range of AC, DC voltage or DC current, and the measuring range is in other positions except AC 10V, read the scale line. The third line, marked 10V, refers to the AC voltage value of 10V. When the change-over switch is in the AC and DC voltage range, read the scale line. The fourth mark is DB, which indicates the sound level. (II) Measuring Circuit The measuring circuit is a circuit used to convert all kinds of measured data into tiny DC current suitable for electric meter measurement, and consists of resistors, semiconductor elements and batteries. It can convert all kinds of measured data (such as current, voltage, resistance, etc.). ) and different self-closing paths become a certain amount of micro DC current after a series of treatments (such as rectification, shunt, voltage division, etc.). ) and send it to the meter for measurement. (3) The change-over switch is used to select various measuring lines to meet the measurement requirements of different types and ranges. Generally, there are two transfer switches marked with different gears and ranges. Second, measure the resistance with a multimeter (1). The measuring principle is actually to measure the current. There is a battery in the multimeter. When measuring resistance, according to ohm's law, the current value is converted into resistance value, and the measured resistance value can be obtained. (2) Measurement step 1. Mechanical zero adjustment. Before the multimeter is used, it should be "mechanically withered", that is, when there is no electricity to be measured, make the pointer of the multimeter point to the position of zero voltage or zero current. However, due to various reasons, when the two pens are separated, the pointer of the electric meter sometimes does not point to the zero current scale, which requires mechanical zero adjustment. The method is: use the spiral knife to turn the mechanical zero-setting screw to drive the pointer to rotate. Make the pointer point to the infinite ohm scale. 2. Select the project. Turn the transfer switch to the "0" position. 3. Select the appropriate amplification gear. The scale line of the multimeter's ohm gear is uneven. Therefore, the comparison block should be selected so that the pointer stays in the thinner part of the scale line, and the closer the pointer is to the middle of the scale foot, the more accurate the reading will be. Under normal circumstances, the pointer should be between 2 12 and 2 12 of the scale. If it is not in this range, you can add 33 gears with large magnification. 4. Ohm zero adjustment. Before measuring resistance, the two probes should be shorted together. At the same time, adjust the ohm (electric) zero knob so that the pointer points to the zero position on the right side of the ohm scale line. The method is as follows: short the two probes together and turn the zero ohm zero adjustment knob at the same time. So that the pointer of the meter accurately stays at the zero point of the ohm scale. If the pointer is not set to zero, it means that the battery voltage is insufficient or there is a problem inside the instrument. And change gears every time. Ohmic zeroing should be performed again to ensure accurate measurement. 5. Connect the measured resistance. Connect the measured resistance to the two probes. 6. study. The reading of the instrument multiplied by the magnification is the resistance value of the measured resistance. When measuring the equivalent resistance of nonlinear components with different ratios of ohms of multimeter. The measure resistance values are different. This is because the median resistance and full-scale current of each gear are different. In mechanical watches, the smaller the ratio, the smaller the measured resistance. 7. Return to the multimeter. After measuring the resistance, turn the transfer switch to the high voltage position. This is a good habit to prevent the misuse of ohmmeter (or current block) to measure voltage. (3) Precautions 1. Before using multimeter. We should fully understand the functions of each change-over switch, special socket, measuring jack and corresponding accessories, and know the reading of its dial. 2. When using the multimeter, it must be placed horizontally to avoid mistakes. At the same time, we should pay attention to avoid the influence of external magnetic field on multimeter. 3. In the process of using multimeter. The metal part of the stylus cannot be touched by hand, which can ensure the accuracy of measurement on the one hand and the safety of people on the other. 4. Can't live measurement, measured resistance can't have parallel branch. 5. When measuring the equivalent resistance of polar components such as transistors and electrolytic capacitors, be sure to pay attention to the polarity of the two pens. 6. After using the multimeter, put the transfer switch in the maximum range of AC voltage. If it is not used for a long time. The battery inside the multimeter should also be taken out to prevent the battery from corroding other devices in the meter. References: E 1] Zeng Xiangfu. Practical electrician skills. Higher education press. [2] Fundamentals of Electrician (second edition). Electronic industry press. 179 Wan Fang data.