For example, speaking; 1, we use electric bulbs, when the switch is closed, the current comes out of the power supply, through the wire to reach the filament, due to the heating of the filament until it emits light, used for lighting this is the physical phenomenon of heat in the electrical transmission in the resistance; 2. The use of electric fans, is the use of electric current flowing through the conductor, the rotating magnetic field generated around the conductor, so that the fan motor rotates (electromagnetic force) to drive the blades rotating and "work" of the physical phenomenon; 3, we put the pot on the stove on the heat (or combustion), and the heat emitted from the stove so that the food inside the pot absorbs heat energy and be cooked, because it is the use of the physical phenomenon of heat conduction; 4, we have a fan or fan can have the wind, is the physical phenomenon of electrical transmission on the resistance of heat; 4, our fans or fans can have the wind, is the physical phenomenon of electrical transmission on the resistance of the heat. or fan can have wind, is the use of other forces to make the two sides of the fan blades to create a different pressure difference, thus creating wind (aerodynamic force); 5, our cars and people can walk on the ground, is the use of friction between objects; 6, we can measure the weight of an object with an ordinary pole scale, is the use of the principle of leverage (mechanics) to achieve the; live physics: 1, chopsticks is the principle of leverage 2, the hour hand of the clock turning is the Elastic potential energy into kinetic energy 3, fluorescent lamps is the use of electromagnetic induction phenomenon of self-induction phenomenon 4, the summer heat to the ground splashing water is the use of the principle of evaporation to reduce the temperature 5, start the car or brakes are unsteady because of the inertia 6, the gas station is located in the open place is because of the inverse ratio of the pressure and the volume, the larger the volume, the lower the pressure, the more likely to be less likely to explode 7, the lights will be on for a long time will heat up because of the current of the thermal effect 8, the TV appears to be the evolution of the oscilloscope 9, by the door clip to the fingers will be deformed is the effect of force 10, people can walk, animals can climb or walk because of the contribution of friction 11, the plane can fly because the flow rate and pressure is inversely proportional to the flow rate of the bigger, the smaller the pressure Soap bubbles why is always the first to rise and then fall in our daily lives, we often see some children blowing soap bubbles, a small soap bubbles from the A small soap bubble from the straw to fly out in the sunlight, sending out beautiful colors.

At this point, the children immersed in joy and happiness, we adults often hope that the soap bubbles can float in the air, forming a beautiful landscape. But we often see soap bubbles at the beginning of the rise, followed by the decline, this is why? This process and phenomenon, we just pay attention to think about it, will find that it contains a wealth of physical knowledge.

In the beginning, the soap bubble is blown from the mouth of the hot air, soap film to separate it from the outside world, the formation of two regions, inside the hot air temperature is greater than the temperature of the outside air. At this time, the density of the gas inside the soap bubble is less than the density of the external air, according to Archimedes' principle can be seen, at this time the soap bubble by the buoyant force is greater than its gravity, so it will rise.

This process is the same as the principle of hot air balloon. With the beginning of the ascent process and the passage of time, the soap bubble inside and outside the gas heat exchange, the internal gas temperature drop, due to thermal expansion and contraction, the soap bubble volume gradually decreased, it is subject to the buoyancy of the outside air will gradually become smaller, and its gravity remains unchanged, so that when gravity is greater than the buoyancy of the soap bubble will fall.

Why is it so quiet after a big snowstorm? In winter, after a big snowstorm, people will feel quiet outside. What's going on? Could it be a decrease in man-made activity? So why does nature return to its former hustle and bustle after the snow has been stepped on? It turns out that the freshly fallen snow is fresh and fluffy.

Its surface layer has many small pores. When sound waves from the outside world enter these pores, they are reflected.

Because the pores are often large inside and small caliber. Therefore, only a small portion of the wave energy can be reflected back through the exit, while most of the energy is absorbed.

As a result, most of the energy of natural sound is absorbed by this surface layer, resulting in a scene of silence. But when snow is stepped on, it's a very different story.

The fresh, fluffy snow is compacted, which reduces the absorption of sound energy. So, nature then returns to its usual clamor.

Why is lightning curved We all know that the two clouds with anisotropic electricity close to the release of lightning, flash channel due to high temperature so that the volume of air rapidly expanding, the vaporization of water droplets and emit a strong explosive sound, which is often referred to as "lightning and thunder". Why is lightning always curved? The U.S. National Weather Service's Nezet Lydell believes that whenever a storm comes, the raindrops will be able to get extra electrons.

Electrons are negatively charged, and these electrons go after positive charges on the ground. When the extra electrons flow out of the cloud, they collide with other electrons, which turn the other electrons into free electrons as well, thus creating a conductive trajectory.

A conductive trajectory jumps and meanders in the middle of irregularly shaped clusters of charged ions scattered in the air, and is generally not a straight line. So the trajectory of lightning is always meandering.

Answer added 2009-10-03 11:40 Physics is a natural discipline with a long history, physical science as an important branch of natural science, not only on the progress of material civilization and human understanding of the natural world to deepen the important role in promoting, but also on the development of human thinking has produced an indispensable impact. From the Aristotelian era of natural philosophy, to the Newtonian era of classical mechanics, until the modern physics of relativity and quantum mechanics, etc., are physicists of the scientific quality, the spirit of science, as well as the tangible embodiment of scientific thinking.

With the development of science and technology, social progress, physics has penetrated into all areas of human life. For example, just find the car in the optical knowledge of the following points: 1. car cab outside the rear view mirror is a convex mirror The use of convex mirrors on the dispersion of light and into the orthogonal, reduced, virtual image of the characteristics of the physical object to see a small, greater range of observation, and to ensure the safety of driving.

2. car headlights in the mirror is a concave mirror it is the use of concave mirrors can be placed on the focus of the light source issued by the light reflected into parallel light out of the nature of the made. 3. 3. car headlamps are always equipped with horizontal and vertical stripes of the glass lampshade car headlamps from the bulb, reflector and lamp front glass cover.

According to the knowledge of lenses and prisms, the car headlight glass cover is equivalent to a combination of lenses and prisms. When driving at night, the driver should not only see the situation of the road ahead, but also to see the roadside holders, road signs, road junctions, etc.

Lens and prisms are the same as a combination of lens and prism.

Lens and prism have a refractive effect on the light, so the lampshade through the refraction, according to the actual need to disperse the light to the required direction, so that the light is uniformly soft.

2. Two small articles about the application of physical knowledge in life (each in about 200 words)

1, liquid evaporation heat absorption

Experiment: the freshly boiled egg from the pot, when held directly in the hand, although hotter, but still

tolerable. After a while, when the water film on the eggshell dried, feel more hot

than just fishing on.

Analysis: Because of a layer of water film attached to the shells of freshly fished eggs, at the beginning, the water film evaporates and absorbs heat,

so that the temperature of the eggshells drops, so it does not feel very hot. After a period of time, the water film evaporates

. The heat transferred from the inside of the egg raises the temperature of the shell again, so it feels hotter.

2, the nature of thermal expansion and contraction

Experiment: the boiled eggs immediately immersed in cold water, to be completely cooled, and then picked up peeled.

Analysis: First of all, the egg was just immersed in cold water, the eggshell directly cold contraction, while the protein temperature drop

is not big, the contraction is also small, this time the main performance of the eggshell in the contraction. Secondly, due to the different substances

nature of the differences in thermal expansion and contraction, when the whole egg are completely cooled, the loose organization of the egg white

contraction rate than the egg shell, contraction is more pronounced, resulting in the egg white shell from each other, peeling the eggshell

is more convenient.

3, verify the existence of atmospheric pressure

Experiment: choose a bottle with a caliber slightly smaller than the egg, in the bottom of the bottle hot layer of sand. First ignited

A ball of alcohol cotton into the bottle, then put a shelled egg small head end down to plug the bottle.

After the flame went out, the egg was slowly "swallowed" into the bottle.

Analysis: alcohol cotton burning bottle gas thermal expansion, part of the gas is discharged. When the egg blocked

bottle mouth, the flame extinguished, the gas inside the bottle due to the temperature drop, the pressure becomes smaller than the bottle outside

atmospheric pressure. Under the effect of atmospheric pressure, the egg, which has some elasticity, is pressed into the bottle.

4, floating and sinking phenomenon

Experiment: put a shelled egg, submerged in a large-diameter glass filled with water. After releasing

open hand, found that the egg slowly sank to the bottom of the cup. Fish out the egg and add salt to the water to make

a concentrated salt solution. Then submerge the egg in the salt solution and let go of your hand, but the egg

slowly floats.

Analyze: The floating and sinking of an object depends on the relationship between the force of gravity and the force of buoyancy. Submerged in the liquid

The volume of the object is the volume of the liquid it discharged, according to Archimedes' principle that the density of the object

The size of the relationship between the density of the object and the density of the liquid can be corresponding to the relationship between gravity and the size of the buoyant force.

Because the density of the egg is slightly greater than that of the water, when the egg is immersed in the water, the force of gravity is greater

than the force of buoyancy, so the egg will sink. When immersed in salt water, which is denser than the egg

, the force of gravity is less than the force of buoyancy, so the egg will float.

5, inertia, frictional resistance phenomenon

Experiment: choose a similar shape of the raw egg, cooked egg each one, placed on a horizontal table. With

the same force to make them rotate in place. The one that spins quickly is the cooked egg, and the one that stops after a few slow rotations

is the raw egg.

Analysis: the shell of the raw egg is liquid egg white, the external force on the shell rotation, the egg white

due to inertia, continue to maintain a stationary state, it and the shell of the friction between the role of resistance, so that

the whole egg can only be slow rotation. And cooked eggs within the egg white has solidified into protein, external forces when rotating

when the whole egg can quickly turn.

6, the object's stable balance

Experiment: choose a raw egg, open a hole in the small end of the head and remove the clean shell egg white and egg

yellow. Slide a weight along the hole. Take the large end of the shell as the bottom and hold the shell. Light

a candle and drizzle in candle oil to seal the weight at the bottom of the shell. Seal the candle oil to about one-quarter of the height of the entire

eggshell. The shell will stand up by itself when you push it down.

To make a "tumbler".

Analysis: In the empty eggshell at the bottom of the sealed weight and candle oil, so that the entire body of the egg's center of gravity close to the bottom of the egg

Shell, the center of gravity from the low, the better the stability. When the shell is tilted away from its equilibrium position,

it raises the center of gravity of the egg. Because the bottom of the shell is spherical, under the action of the egg's own gravity

, the egg returns to its original equilibrium position.

7, the phenomenon of molecular motion

Experiment: shell intact eggs, buried in salt for a period of time, can be made into a salted egg.

Although the shell is still intact, but even the internal yolk is salty.

Analysis: Because there is a gap between the molecules of a substance, and the molecules keep moving irregularly,

so the salt molecules diffuse into the yolk, making the yolk salty.

3. Physical experiments in life

(1) summer from the refrigerator that out of the beer bottle "sweat": water vaporization into small droplets attached to the bottle.

(2) Ice flowers on the windows in winter: water vapor condensation.

(3) Wake up in the morning to see fog: the phenomenon of liquefaction of water vapor in the air.

(4) Frozen clothes dry out in winter: sublimation of ice.

(5) Water boils at different times and places: differences in atmospheric pressure.

(6) Water can only boil dumplings white, while oil can fry them yellow: the boiling point of oil is higher than that of water.

(7) Mirage phenomenon: light is deflected due to encountering uneven atmosphere.

(8) Small holes make an inverted image: light travels in a straight line.

(9) A plane mirror can image: reflection of light.

(10) Stretching into the water chopsticks bent: light oblique into another medium and the phenomenon of refraction

4. Physical knowledge in life

Physical knowledge in the kitchen We carefully observe the kitchen fuel, cooking utensils, cooking, cooking and other all the process, recall a series of changes occurring in the kitchen, you will see the relevant physical phenomena.

Explain these phenomena using knowledge of physics as follows. First, the phenomenon related to knowledge of electricity 1, electric rice burger cooking, electric frying pan cooking, electric kettle boiling water is the use of electrical energy into internal energy, are the use of heat transfer cooking, cooking, boiling water.

2, exhaust fan (range hood) using electrical energy into mechanical energy, the use of air convection for air transformation. 3, rice cooker, electric frying pan, electric kettle three-pronged plug, inserted into the three-hole socket to prevent electrical appliances leakage and electrocution accidents.

4, the microwave oven heating evenly, high thermal efficiency, health and pollution-free. The heating principle is to use electrical energy into electromagnetic energy, and then electromagnetic energy into internal energy.

5, the kitchen lights, the use of the thermal effect of the current work, the conversion of electrical energy into internal energy and light energy. 6, kitchen stoves (cellular coal stove, liquefied petroleum gas stove, coal stove, wood stove) is the conversion of chemical energy into internal energy, that is, fuel combustion to release heat.

Second, the phenomenon related to the knowledge of mechanics 1, electric kettle spout and pot belly constitutes a connector, the water surface is always flat. 2, the thin blade of the kitchen knife is to reduce the force area and increase the pressure.

3, kitchen knife blade has oil, in order to cut vegetables, so that the contact surface is smooth, reduce friction. 4, kitchen knife handle, spatula handle, electric kettle handle has convex and concave pattern, so that the contact surface is rough, increasing friction.

5, fire shovel to send coal, is to use the inertia of the coal into the fireplace. 6, pour boiling water into the thermos, according to the sound to know the amount of water high and low.

As the amount of water increases, the length of the air column decreases, the vibration frequency increases, and the pitch rises. 7, grinding kitchen knives to constantly pour water, because the knife and stone friction work to generate heat so that the internal energy of the knife increases, the temperature rises, the hardness of the knife becomes smaller, the knife is unfavorable; pouring water is the use of heat transfer so that the knife's internal energy decreases, the temperature decreases, will not rise to too high.

Third, the phenomenon related to thermal knowledge (a) and thermal expansion and heat transfer phenomena related to thermal 1, the use of stoves to boil water or stir-fry, to make the bottom of the pot on the outer flame of the fire, do not let the bottom of the pot to press the head of the fire, the temperature of the pot can be made to rise quickly, because the fire's outer flame temperature is high. 2, spatulas, spoons, spoons, funnels, aluminum pots and other cooking utensils handle made of wood, because wood is a poor conductor of heat, so that in the process of cooking is not hot.

3, the stove above the installation of exhaust fans, is to speed up air convection, so that the kitchen fumes in a timely manner to avoid contamination of space. 4, boiling hot casserole on the wet ground is easy to rupture.

This is because the casserole is a poor conductor of heat, hot casserole on the wet ground, the casserole outer wall rapidly exothermic contraction and the inner wall of the temperature is slow to reduce the casserole inside and outside of the contraction is not uniform, it is easy to rupture. 5, to the thermos bottle filled with boiling water, not filled with better insulation.

Because the bottle is not full, there is a layer of air, is a poor conductor of heat, can better prevent heat loss. 6, frying is mainly the use of heat conduction way of heat transfer, cooking, boiling water, etc. is mainly the use of convection way of heat transfer.

7, winter from the thermos pour out some boiling water, cover the stopper, often see the stopper immediately jump. This is because with the boiling water poured out, into some cold air, corked tightly, into the cold air is heated quickly expanded, the pressure increases, thus pushing the cork.

8, winter just out of the pot of hot soup, see the soup surface is not hot, as if the soup is not hot, but drink it is very hot, because there is a layer of oil on the surface of the soup to hinder the soup within the heat dissipation (water evaporation). 9, winter or very low temperatures, pour boiling water into the glass, you should first use a small amount of boiling water to preheat the cup, in order to prevent the glass inside and outside the temperature difference is too large, the inner wall of the thermal expansion by the outer wall of the obstacle to generate force, resulting in a cup rupture.

10, after boiling hot eggs into cold water for a while, easy to shell. Because the rolling hot egg shell and protein will shrink when cold, but they do not shrink to the same extent, thus making the two detached.

5. "Physics in life" inquiry report

We are stepping into an era of knowledge economy based on intellectual resources and information resources, and a new economic form with innovation as the soul.

People-oriented, cultivating talents with innovative spirit and practical ability is the inevitable choice and historical mission of education to face the industrialization of high technology and the era of knowledge economy. Therefore, "moral education as the core, to the spirit of innovation and practical ability training as the focus of" quality education, the important focus is to change the students simply accept the teacher's knowledge transfer learning mode, to help students in the acceptance of learning at the same time, the formation of a knowledge of the active search, and pay attention to the actual problem solving active learning mode.

To this end, the 1999 revision of the physics syllabus for the first time proposed to carry out research learning activities in the teaching of general senior secondary schools, which is an important initiative of the reform of China's high school physics curriculum. Since the 1990s, the United States, Britain, France, Japan, Australia, Norway and other countries and Taiwan Province of China in the basic education curriculum reform, are focused on the opening of research-based courses.

Some regions (Shanghai, Beijing) or schools in China, have also been the first to carry out the development and research of research-based curriculum, research-based learning exploration and practice. From the practice of opening research-based learning at home and abroad, research-based learning is a reform of the traditional receptive learning, is to cultivate students' innovative spirit and practical ability of the new concept of education in the field of teaching.

At present, with the opening of the new textbooks across the country, how to design and implement physical research learning activities has become a new topic that the majority of educators need to be resolved, in order to avoid the blindness of the research learning activities, not to make the research learning a formality, but rather to be able to give full play to its advantages of the role and educational functions, it is necessary to carry out the study of this topic, aiming to make this new type of learning mode to achieve better results. We will carry out research on the design and implementation of high school physics research study on the basis of domestic and international experience in the design and implementation of research-based courses.

Second, the basic idea of the study (a) the concept of definition and research hypothesis According to the new physics syllabus, research-based learning in general teaching refers to the students under the guidance of teachers, according to their interests, hobbies and conditions, from the study of life and social life to choose different research topics, similar to the way of scientific research, take the initiative to get the information, and the use of the knowledge they have learned to analyze, Discuss and even solve practical problems of learning activities. Physics research study includes exploratory physics experiments, science and technology production, research and study of new scientific and technological issues, social research, history of physics research, extended learning and other types.

Its goal is to comprehensively cultivate students' ability to comprehensively apply what they have learned in the process of research learning, the ability to collect and process information, the ability to analyze and solve problems, the ability to express themselves in writing and language, the ability to lead, organize, manage, and unite and collaborate, etc.; to cultivate students' habit of independent thinking, and to stimulate the students' sense of innovation. 1, the positioning of physical research learning Physical research learning activities and teaching of physical subjects have more different characteristics, in the specific design and implementation, the need to accurately position, grasp the design and implementation of the focus and direction.

①Research learning is mainly to provide students with an opportunity to synthesize and practice the knowledge learned in the classroom and the existing experience, to cultivate the spirit of innovation and hands-on practical ability, rather than confined to the general understanding and mastery of textbook knowledge. ② The implementation of research study is similar to the process of scientific research, but not in the usual sense of scientific research.

In the research study, "research" is only the carrier, not the purpose, it is only an important means of accomplishing the goal of education. Research study is a compulsory course for all high school students, not just a course for a few outstanding students.

It pursues the goal of stimulating students' initiative to explore and cultivating their spirit of innovation, encouraging students to intervene in research on the frontiers of the discipline, and requiring students' research results to be scientific, but not requiring that each student's final research results must be innovative. ④Based on students' knowledge, ability and experience, it emphasizes the connection between the research content and the original knowledge, ability and experience, and promotes students' learning through the development of research-based learning.

2, the research hypothesis (1) if from discipline-centered to learner-centered change, actively carry out research learning in physics, can make students understand that physical knowledge in modern life, social production, science and technology has a wide range of applications, understanding of physics and other disciplines as well as the relationship between physics and technological progress, social development. (2) If the implementation of discipline synthesis in physics teaching, knowledge and ability to synthesize, and actively carry out physics research study, can make students by the scientific method of training, cultivate students' observation and experimental ability, scientific thinking ability, the ability to analyze and solve problems.

(3) If the physics teaching from the "maintenance of learning to anticipatory, creative learning", to carry out physical research learning, can cultivate students' interest in learning science and establish a scientific attitude of seeking truth from facts, cultivate a sense of innovation, learn to innovate in order to solve unknown problems. This is very important for them to improve the quality of science and culture, adapt to modern life, continue to learn science and technology.

(2) research purpose and value 1, research purpose Through the analysis of the current situation of the teaching process, the exploration of the law of teaching and learning, and strive to advanced education and teaching concepts as a guide to the coordinated development of students' ability, personality, knowledge as the goal, to build the teaching mode of physical research learning, enrich the implementation of comprehensive practical activities course ways and means, and to further broaden the connotation of the existing research learning and extension, to enrich the educational and teaching theory of research learning, to reflect the new learning mode of research learning from the practical level, to reveal the inevitable connection between research learning and the teaching and learning of subject knowledge, to promote the development of research learning activities in the discipline of physics, and at the same time, to provide new ideas for related research. 2, the research value of research learning will change the students simply accept the teacher's knowledge transfer learning mode, to help students in the acceptance of learning at the same time, the formation of a kind of active search for knowledge, and attach importance to practical problem solving active learning style; it is conducive to the full release of students' creative potential, so that the students' individuality and strengths have been fully developed; is conducive to the organic synthesis of students' knowledge and ability, the organic combination of theory and practice, and is conducive to a new kind of knowledge and ability. Organic combination of practice, in favor of a new.

6. Examples of practical applications of physical knowledge in daily life (150) words or so

For example: rural tap water using the principle of connectors

Centrifugal pumps can be pumped to the motor turbine at the use of atmospheric pressure

Hydraulic jacks utilize the pressure of a certain area of force and the magnitude of the force of inverse relationship

Pliers use a lever, a lever, a lever, a lever, a lever, a lever, a lever, and a lever, a lever, a lever, a lever, a lever, a lever, a lever, a lever, a lever, a lever, a lever, and a lever. p> The pliers make use of the principle of leverage

The anti-lock system of a car makes use of the fact that the maximum static friction is greater than the sliding friction

The sole of the shoe is made with an uneven pattern to increase the friction factor and increase the friction force, and the same is true of the tires of a car.

A hydroelectric power plant is an energy conversion by converting the gravitational potential energy of water into kinetic energy and then into electrical energy

And so on. If you think about it, physics is everywhere. Most of the phenomena around you have applications of physics

7. Seek a point of physics experiment report, is related to the daily life of the interesting physical phenomena, urgent

I have done a few experiments report, the format is like this:

Name of the experiment: to explore (research) ______________/factors affecting the ____________

Purpose of experiment: (usually the same as above) ______________

Experimental equipment: ______________

Experimental steps: _______________________________________

_______________________________________

_______________________________________

Experimental conclusion: _____________________________

Experimental inference: (optional) ______________________

Experimental report is best to be written on your own

I can provide some experimental phenomena in life:

1, the formation of the rainbow (dispersion of light, spectra)

2, the different sinking and floating of the egg in the water and the salt water (the state of the object sinking and floating and liquid density relationship)

3, the size of the tap water flow rate in the faucet by the pump pressure (the relationship between liquid pressure and flow rate)

......

8. Physics in life

Physics experiments play an important role in the teaching of physics. Through the analysis of the experimental phenomena, to remove the coarse and extract the essence, to remove the false and save the truth, from which to summarize the laws of physics, which is an important means of experimental teaching. In the teaching method, in order to help students understand the laws of physics, a variety of textbooks are arranged in close conjunction with the teaching content of the experiment. In particular, the teacher's demonstration experiments and do a do experiments for students to study and explore the laws of physics is very useful. But some of the experiments will appear in some of the phenomena have little to do with the purpose of the experiment, here I call it secondary phenomena. Sometimes these phenomena appear in-depth study will increase the students' horizons, the quality of the improvement is favorable. But some experiments are not done properly, the purpose of the experiment will not achieve the desired results, will inevitably affect the knowledge of the laws of physics. I encountered in the physical teaching of the actual situation summarizes a few examples for reference by colleagues.

First, the capacitor with DC, AC demonstration experiments

In the demonstration of capacitors across DC, AC experiments, if the capacitance is too large, the resistance of the bulb is also larger, the moment of connecting the DC, the bulb to flash, and then extinguished. If this phenomenon occurs in the demonstration to the students, the teacher should seize this great opportunity to allow students to study and discuss, both for the review of old knowledge, but also conducive to the deepening of new knowledge. Then summarize the light bulb flash is caused by the capacitor charging current. And then the capacitor is charged, and then let the students observe the capacitor on the light bulb discharge when the light bulb flash. This is an additional experiment to observe the charging and discharging of a capacitor. Since the current is not continuous and can only be maintained for a short period of time, it shows that the capacitor can not pass DC current continuously in a DC circuit.

Assume that in order to emphasize the experiment, not to complicate things, so that the value of the capacitor should not be too large to do this experiment, the bulb resistance should be small. At the moment of turning on the DC current, the charging current is not enough to ignite the bulb. From the phenomenon, indisputable, capacitance is isolated from DC, so that the experiment is ideal.

Second, to verify that the transformer can not change the DC voltage demonstration experiment

In order to verify that the transformer can not change the DC voltage, I have used the DC output of the JL201-1 low-voltage power supply, and with a detachable transformer and a small bulb to observe. And after powering up the experiment, the light bulb continuously and stably light. What's going on here? Is the transformer can change the DC power? This is not possible! Then what is the cause? After analysis found that the root cause is the DC output of the low-voltage power supply to send out the pulsating DC power, that is, DC contains AC components of the current. This is because the low voltage power supply bridge rectifier voltage is not filtered and sent out directly.

This problem was identified without demonstrating it to the students. Assuming a direct classroom demonstration, this will inevitably lead to a false conclusion that the transformer can change the DC voltage. In order to remove the falsehood, a 2500μF50V electrolytic capacitor can be connected in parallel to the DC output terminals, the experimental effect is the same as with a battery or dry cell. Therefore, with a low-voltage power supply or student power DC output to do experiments related to capacitance and inductance, additional large-capacity capacitor filtering.

Assuming that the purpose of this experiment is not only to verify that the transformer can not change the DC voltage, but also to introduce the study of pulsating DC. Then, can be demonstrated first with a battery or dry cell, and then do the above unsuccessful experiment. Guide students to analyze and compare the two experiments why the conclusion is not the same, fully mobilize the students to explore the consciousness, so will not achieve the purpose of a two-pronged approach!