The first chapter is the phenomenon of sound.
Section 1 Generation and Propagation of Sound
One: the generation of sound
1. Sound is produced by the vibration of objects.
Conditions for vocalization: first, there must be a vocal body; Second, the vocal body should vibrate.
2. Vibration object sound source.
3. Everything that makes a sound is vibrating, the vibration stops, and the sound stops, but the sound doesn't necessarily stop.
4. Gases, liquids and solids can all make sounds due to vibration.
For example, wind, rain, reading sound and reading sound are the sounds made by the vibration of gas, liquid and solid respectively.
Two: the spread of sound
1. Sound needs media to spread. Solids, liquids and gases are all media, and vacuum cannot spread sound.
For example, astronauts on the moon can only talk by radio waves. Sound travels in the form of sound waves
2. Sound speed: the distance that sound travels every second.
The speed of sound propagation is related to the type and temperature of the medium.
Sound travels fastest in solid, second in liquid and slowest in gas. At 15℃, the propagation speed of sound in the air is.
3. Echo: The sound is reflected when it meets an obstacle, and then it is introduced into the human ear to form an echo.
Only when the echo reaches the human ear more than 0. 1 second later than the original sound, or when the obstacle is at least 17 meters away from people, can the human ear distinguish it from the original sound, otherwise it will be mixed with the original sound to enhance the original sound.
Note: 1. Don't think that as long as an object vibrates, it will certainly make a sound that people can hear.
2. Don't think that as long as you hear the sound twice, it must be an echo, and if you don't hear it twice, there must be no echo.
essay question
1. Is the continuous thunder heard during thunder formed by continuous thunder? Why?
A: No, the continuous thunder heard during thunder is the result of the sound being reflected by mountains and clouds many times, forming an echo.
2. In the summer of 2002, five students in Peking University climbed Mount Everest and an avalanche occurred, which caused a serious accident. Please analyze: why don't you shout loudly when climbing in the snow?
A: When climbers or explorers enter snow-capped mountains or caves, it is generally forbidden to make loud noises. This is because the support of snow drifts on mountains and rocks in caves may be very fragile. Shouting loudly will cause air vibration, and when it reaches snow drifts or rocks, it will cause them to vibrate, which may cause avalanches or cave collapses, thus endangering people's lives and property. Therefore, don't make any noise when entering such areas.
Please imagine what will happen in our world if the speed of sound is 0. 1m/s? Please write four relevant and reasonable scenarios.
Answer: (1) When two people talk face to face, it takes some time to hear clearly.
(2) Thunder cannot be heard for a long time after lightning;
(3) It takes a long time for athletes to start after the starting gun goes off;
(4) When setting off fireworks, it will take a long time to hear the salute after seeing the fireworks.
Xiao Ming wants to measure the speed of sound propagation in the air. Please help Xiao Ming design an experimental scheme and write out the experimental equipment and steps.
Methods 1: Equipment: starting gun, scale and stopwatch.
Step: (1) Measure the distance s from the release place to the timing place with a scale;
(2) Let the starting gun go off and let another person record the time t from seeing the smoke to hearing the noise at the timing place;
(3) calculate the speed of sound with formula v = s/t. ..
Method 2: Equipment: weighing scale and stopwatch.
Steps: (1) Stand away from the building and shout, and record the time t from shouting to hearing the echo;
(2) Measure the distance s between people and tall buildings with a ruler;
(3) Calculate the sound speed with the formula V = 2s/t. ..
Xiao Li wants to verify the conclusion that "sound communication needs media". Please help her design an experiment to illustrate the correctness of this conclusion.
Answer: Equipment: alarm clock, glass cover, exhaust fan.
Methods: The alarm clock was placed in a sealed glass cover, and the air in it was gradually pumped out by an air pump. It is found that the bell is getting smaller and smaller, and finally the bell can't be heard, which proves that sound transmission needs media.
How do we hear voices in the second quarter?
One: the structure of the human ear (omitted)
2.1.The process of human hearing sound: external sound causes vibration, which is transmitted through other organizations, transmitting signals and making people hear sound.
2. Two ways of sound transmission:
① air conduction; ② Bone conduction.
3. Two ways for human ears to hear sound:
① Sound waves-auricle-external auditory canal-tympanic membrane-ossicular bone-auditory nerve-brain.
② Sound wave-ossicular bone-auditory nerve-brain.
4. The human ear must have the conditions to hear sound:
First, the sounder vibrates 20-20000 times per second;
Secondly, there must be a medium to spread sound;
Third, there must be a good organ (human ear) to receive sound.
Three: Binaural effect:
The distance from the sound source to the two ears is generally different, and the characteristics such as the time when the sound reaches the two ears are also different, so that the position of the sound source can be judged.
Application: Because of binaural effect, all the sounds we hear are stereo.
Note: don't think that people can't perceive sound without hearing.
essay question
1. Let a classmate sit in the middle of the classroom blindfolded. Then, you stand in front of or behind your classmates and clap your hands. Can students accurately judge where you clap your hands? Why?
Answer: You can't correctly judge the position of the high-five, because people judge the direction of the sound source through the "binaural effect", and when you stand in front of or behind your classmates and high-five, the distance from the sound source to both ears is the same, so there is no difference in the time felt by both ears, and there will be no binaural effect, so you can't accurately judge the direction of the sound.
2. After Beethoven was deaf, he just bit one end of the stick with his teeth, and the other end leaned against the piano to listen to the sound of his playing, so as to continue his creation. Please explain the reason.
Answer: Sound can also reach the auditory nerve through the skull and jaw, causing hearing. Beethoven wrote in this way, that is, bone conduction.
3. If you are a stage sound engineer, how can you make the audience hear better stereo?
Answer: Put more microphones around the sound source, and correspondingly put more speakers (sound boxes) around the audience, so that the audience can hear better stereo sound.
4. Bite the watch with your teeth and cover your ears with your hands. You will hear the ticking sound strengthened many times. What does this mean?
A: Bones can transmit sound, and the sound transmission effect is very good.
Many deaf people with complete internal hearing can dance to the beat of music. Do you know why?
Answer: This is because the sound of music reaches the eardrum through the floor and his bones, making it vibrate to produce hearing.
The characteristics of the voice in the third quarter
One: Tone
1. Concept: The sound level is called tone.
2. Determinant: Determination of the vibration frequency of the sound generator. The higher the frequency, the higher the pitch.
3. Frequency: 1 second, the number of times the sounding body vibrates, unit: Hz, symbol: Hz.
The hearing range of human ear: 20-20000 Hz. The sound below 20 Hz is called infrasound, and the sound above 20000 Hz is called ultrasonic.
(The frequency of contraction waveform is high)
Second: Loudness.
1. Concept: The strength (size) of sound is called loudness.
2. Determinant: the amplitude of the vocal body determines.
The greater the amplitude, the greater the loudness. Loudness is also related to the distance between the human ear and the vocal body. The farther away from the vocal body, the less loudness.
3. Ways to improve loudness:
One is to reduce the dispersion of sound; The second is to reduce the distance from the human ear to the sound source.
Three: timbre
1. Concept: the quality of sound.
2. Determinant: the vocal body itself
Note: Don't think that the loudness must be high just because the sound is high.
essay question
1. Pour boiling water into an empty thermos. How did the sound from the thermos come from? What is the changing law of this sound?
Answer: When the thermos bottle is filled with water, the air column on the water surface vibrates and makes a sound. As the water surface rises, the air column above becomes shorter and the vibration of the air column accelerates, making the tone emitted by the air column higher and higher. The vibration amplitude and loudness of the air column become smaller.
In winter, the cold wind blows on the wires in the wild, making a purring sound, which can't be heard in summer. Why?
Answer: Due to the cold weather in winter, the wires contract due to cold, and the vibration frequency is high and the tone is high; In summer, the weather is hot, the wires expand and relax, the vibration frequency is low and the tone is low.
When a bee flies with nectar, its wings vibrate 300 times per second on average, and when it doesn't carry nectar, it vibrates 440 times per second on average. Experienced beekeepers can tell whether bees have collected nectar. What is the basis for this?
A: Depending on the tone of the voice. When bees carry nectar, the frequency of wing vibration is small (300 times/second) and the tone is low; Without nectar, the vibration frequency of wings is high (440 times per second), with high frequency and high tone.
People can't hear the sound of butterflies flying, but they can hear the hum of mosquitoes flying around. Why?
Answer: The frequency range of sound that can cause human hearing is 20~20000Hz, and the frequency of butterfly wing vibration is less than 10Hz, which is lower than the hearing range of human ears, so human ears can't hear the sound of butterflies flying; The vibration frequency of mosquito wings is 500~600Hz, and within the hearing range of human ears, human ears can hear the sound made by mosquitoes when flying.
The harm and control of noise in the fourth quarter
1. The concept of noise: ① the sound produced when the sounding body vibrates irregularly.
(2) All sounds that affect people's normal study, work and rest, as well as those that interfere with people's listening, belong to noise.
Two: the level and harm of noise
1. People use decibels (dB) to express the intensity of sound.
2. The lower limit of hearing is 0 dB, and the sound shall not exceed 90 dB; In order to protect hearing; In order to ensure that the voice of work and study cannot be surpassed; In order to ensure rest and sleep, the sound should not exceed 50 decibels.
3. Noise control:
1. Control noise generation; 2. Stop the spread of noise;
3. Weakening in human ears.
Note: don't think that beautiful music must not be noise;
Don't think that the sound of 0 dB means that there is no sound and no object vibrates.
essay question
1. Some people say that music is musical sound, so musical sound will not become noise. Do you think this view is correct?
A: This view is wrong, because from the perspective of environmental protection, all sounds that hinder people's normal rest, study and work are noise, and sounds that interfere with what they want to hear are also noise, so music sounds can be turned into noise.
2. Why is silent pistol "silent"?
Answer: Because the silent pistol attenuates the sound at the sound source, this is the first way to attenuate the noise.
3. The sound transmission performance of the wall is much better than that of the air, but after the doors and windows are closed, the sound coming into the room from the outside is obviously weakened. Why?
A: Sound travels in the air. When it meets obstacles such as walls and glass, most of it will be reflected back. Therefore, after the doors and windows are closed, the sound transmitted to Yin will be weakened, which is a way to reduce the noise during transmission.
4. Why do civilized and sanitary cities require planting trees and grass?
A: Planting trees and grass can not only beautify the city, but more importantly, trees and flowers can absorb and reduce noise, make the city quieter, let people relax and enjoy nature.
If you are a planner of urban construction, what measures will you take to reduce the harm caused by noise?
Answer: ① Plant trees and grass; ② Set up sound insulation boards; ③ Factory, workshop, entertainment places, etc. Away from residential areas ④ It is forbidden to whistle in urban areas.
6. The noisy roads in winter are especially quiet after snowfall. What is the reason?
A: The noise on the road mainly comes from the noise made by various motor vehicles. After the snowfall, the road was covered with a thick layer of snow. At this time, the snow on the road is softer and becomes a better sound-absorbing material, and the noise is absorbed by the snow. Therefore, the road after snowfall is much quieter than usual.
Section 5 the use of sound
One: the use of sound to convey information:
Such as b-ultrasound, sonar,
Second, the use of sound to transmit energy:
Such as ultrasonic cleaning precision instruments; Crushing the substance with ultrasonic waves; Ultrasonic dust removal and tooth cleaning.
Note: Don't think that long-distance measurement must use sonar.
[Experiments and Problems]
1. There is a scene in the science fiction film: a spaceship is in distress in space. On the way to rescue another ship, it suddenly heard the loud explosion of the ship in distress, and then saw the explosion fire. Please point out two scientific mistakes in this scene to the director.
Answer: (1) An explosion was heard in space (no explosion was heard in vacuum).
(2) first hear the explosion and then see the fire of the explosion (the speed of light is greater than the speed of sound)
2. What is the difference between the propagation of light and sound?
Answer: (1) Light can propagate in a vacuum without medium; The transmission of sound needs medium, and vacuum cannot transmit sound.
(2) Generally speaking, the greater the density of the medium, the smaller the speed of light, but the greater the speed of sound.
(3) The speed of light is much faster than the speed of sound.
3. Why do you speak louder in the house than in the wild?
Answer: When talking in a room, the echo and the original sound are mixed together to strengthen the original sound, so it sounds louder.
The wall of the cinema projection hall is decorated with potholes, commonly known as "swallowing mud". What is its purpose?
A: Mud swallowing is bumpy. Its function is to prevent the sound hitting the wall from being reflected to the audience, thus avoiding reverberation, that is, weakening the echo.
Chapter II Phenomena of Light
Section 1 The Propagation of Light
One: light source: the object that can emit light is called light source.
Two: the spread of light
1. Light travels in a straight line in the same uniform transparent medium.
For example, the propagation path of light in air, water and glass is a straight line.
2. Light can also propagate in a vacuum without medium.
3. Applications: solar eclipse, lunar eclipse, pinhole imaging, shadow formation, etc.
Third: the speed of light
1. The speed of light in vacuum is the fastest in the universe, which is represented by the letter C, where c=, and the speed of light in air is very close to that in vacuum. Others believe that the speed of light is in a vacuum in water and in a vacuum in glass.
Note: 1. Because the speed of light is much faster than the speed of sound, lightning occurs at the same time when it thunders, but it is always seen first and then heard.
2. Light year is the distance that light travels in one year, and light year is the unit of length. 1 light year = m.
Error-prone point: ignoring the condition of straight line propagation of light.
[Experiments and Problems]
Please design an experiment to verify that light travels in a straight line in a uniform medium.
Answer: Method 1: Find two pieces of cardboard, dig two small holes in them and illuminate them with a flashlight. It is found that only when two small holes are in a straight line can light pass through, which shows that light propagates in a straight line in a uniform medium.
Method 2: light a mosquito-repellent incense and let the laser beam pass through the smoke. It is found that the red laser beam propagates along a straight line, which shows that light propagates along a straight line in a uniform medium.
Method 3: Spray the air freshener along the laser irradiation direction, and it is found that the red laser beam propagates along a straight line, indicating that light propagates along a straight line in a uniform medium.
Method 4: After the plastic bottle is filled with smoke, it is sealed with a bottle cap to let the laser beam enter from the bottom of the plastic bottle, which shows that light travels in a straight line in a uniform medium.
Method 5: Drop a few drops of milk into a glass filled with clear water, shake well and let the laser beam shoot vertically into the water. It is found that the red laser beam propagates in a straight line in water, which shows that light propagates in a uniform medium.
Please design a method to estimate how far lightning is from you.
Answer: When you see lightning, press the stopwatch immediately and start timing. Press the stopwatch again when you hear the thunder. This time is the time when thunder reaches your ears from where it happened. Multiply the propagation speed of sound in the air by the propagation time of thunder, and you can find the propagation distance of thunder (that is, s=v sound T), that is, the distance between you and the place where thunder occurs. Because in air, the speed of light is much faster than the speed of sound, so the propagation time of light is very short and can be ignored.
Madame Marie Curie wanted to test students' observation and imagination one day and asked, "What is the biggest shadow you have seen so far?" While other students were still thinking hard, it took one of them only one minute to make the correct answer. Can you answer that?
A: At night. Shadows are formed by the linear propagation of light. Among the shadows we usually see, the biggest one is the night. When the sun is on the other side of the earth, our side, due to the linear propagation of light, forms the shadow of the earth, that is, the night.
4./kloc-Does the timekeeper of 0/00 meter finish counting the time when he hears gunshots or sees smoke? Why?
Answer: the starting gun should start timing when it smokes, because the speed of light is much faster than the speed of sound in air. If you wait until you hear a gunshot, you will miss the time required for sound to propagate in the air 100m, that is, t = s/v =100m/(340m/s) = 0.29s. 。
In front of a government office building, a five-star red flag fluttered on the flagpole. Please design a scheme to measure the height of flagpole according to the law of straight line propagation of light.
Answer: Just measure the length of a bamboo pole and the shadow length of the flagpole with a scale. Stand the bamboo pole beside the flagpole and measure the shadow length of the bamboo pole. According to the length of bamboo pole/shadow length of bamboo pole = length of flagpole/shadow length of flagpole, we can get the length of flagpole = (length of bamboo pole × shadow length of flagpole)/shadow length of bamboo pole.
The reflection of light in the second quarter
One: 1. Reflection of light:
When light is emitted from one substance to the surface of another, some light will return to the original substance and spread.
When light strikes the surface of all objects, it will be reflected. We can see non-luminous objects because their reflected light enters our eyes.
2. Six basic elements: "one point, two angles and three lines"
3. Law of light reflection:
(1) reflected light, incident light and normal line are on the same plane;
(2) reflected light and incident light are separated on both sides of the normal;
③ The reflection angle is equal to the incident angle;
④ The optical path is reversible.
When light is incident vertically on the surface of an object, the reflection angle is equal to the incident angle and equal to degrees.
Two: specular reflection and diffuse reflection
1. When parallel light shines on a smooth surface, the reflected light is still parallel, which is called specular reflection.
2. The parallel light hits the rough surface, and the reflection of the reflected light spreading around is called diffuse reflection.
3. Similarities and differences between specular reflection and diffuse reflection
Specular reflection
diffuse reflection
* * * Similarities
When each ray is reflected, it follows the law of light reflection.
discrepancy
The reflecting surface is a plane with smooth surface, and the parallel light beam is still parallel light after reflection.
The surface of the reflecting surface is rough and uneven, and parallel light is reflected in all directions.
Application example
The light reflected by the plane mirror can illuminate the bottom of the well.
Use rough white cloth as a curtain to show the film.
Error-prone point: 1. Distinguish specular reflection from diffuse reflection.
2. The reflection angle and incident angle cannot be correctly judged.
essay question
1. Turn off the lights at night to make the room darker. Spread a piece of white paper on the desktop and put a small flat mirror on the paper, so that the flashlight can point directly at the flat mirror. From the side, is the mirror bright or the white paper bright? Why?
A: White paper is bright. Because the mirror surface of a plane mirror is smooth and reflects, the light vertically incident on the mirror surface is vertically reflected back. Seen from the side, almost no light enters our eyes, so the flat mirror looks very dark; However, the surface of the white paper is rough, and the white paper is diffuse, and the reflected light shines in all directions, so from the side, the white paper is brighter.
The night after the rain, it just cleared up. Although the ground was dry, there were still many puddles. In order not to step on the pool, how should we judge where there is water?
A: The water is flat, just like a flat mirror. When the light shines on the water in the month, there will be specular reflection, and all the reflected light points in the same direction. When people face the moon, a lot of reflected light will enter the human eye, so it seems that these puddles are bright. When people turn their backs to the moon, almost no reflected light enters the human eye, so it looks like these puddles are dark. However, the road surface is uneven, and when the light shines on the road surface in that month, it will diffuse and reflect light in all directions. So it is darker than the horizontal plane in the moonlight, and brighter than the water surface in the moonlight. Therefore, when walking against the moonlight, the brighter place on the ground is the pool; Walking with the moonlight on your back, there is a pool in the darkness on the ground.
3. Why is the blackboard "reflective" and I can't read clearly? How to make the blackboard not "reflective"?
A: When we look at the blackboard, the light that enters our eyes has two parts: one part is the light that is diffusely reflected on the chalk characters; The second is the diffuse light from the blackboard around the characters. The former is stronger than the latter, so you can see the characters on the blackboard clearly. If the blackboard at the writing place is smooth, there will be specular reflection, which will reflect the same amount of incident light to the blackboard in the same direction. In this direction, the strong light reflected by the mirror masks the weak light reflected by the chalk, so the chalk cannot be seen clearly. To make the blackboard not "reflective", it is necessary to make its surface rough, for example, brush blackboard paint on ground glass so that it does not reflect the incident light specularly.
Section 3 Plane Mirror Imaging
1. Characteristics of plane mirror imaging
(1) image is an upright virtual image, and the image and object are symmetrical about the plane mirror.
(2) The image and the object are equal in size.
The image is the same size as the object and has nothing to do with the distance of the plane mirror, so it can't be felt only by the visual effect of the human eye.
(3) The connecting line between the image and the object is perpendicular to the mirror surface, and the distance between the image and the object and the mirror surface is equal.
(4) Image is the opposite of things.
The wonderful thing is that the objects are equidistant and the sideline is perpendicular to the mirror.
Example Xiaowen stood in the plane mirror 3m, and saw his own image in the mirror, which was formed by the phenomenon of light. The distance from her image to the mirror is meters; When she approaches the mirror at 1m, the distance from the image to her is m.
2 Virtual image
(1), point imaging
As shown in the picture in the textbook, there is a luminous point S in front of the mirror, which can emit countless rays. Draw two rays SA and SC, which will enter people's eyes in the direction of AB and CD after being reflected by the mirror. When people look against the direction of reflected light, it seems that these light rays come from their intersection point S 1 on the extension line behind the mirror, just like the feeling that there is a luminous point at S 1.
(2) Volume imaging
A mirror object can be regarded as composed of many points, and each point has an image in the mirror, which constitutes the image of the object, so it can be seen that the image of the object in the plane mirror is also a virtual image.
The application of virtual image is not formed by the convergence of actual light, but by the intersection of reverse extension lines of reflected light.
The shadow of Shuangjiang Tower is one of the famous "Ten Scenes of Wuhu". Looking north from Zhongtong Bridge, Zhongjiang Tower stands on the bank at the intersection of Qingyi River and Yangtze River, hidden in the sunlight and water, as shown in the picture. "Tower shadow" is actually formed by light (fill in "real image" or "virtual image").
2. The application of flat mirror
1, only changes the propagation direction of the beam, but does not change the convergence and divergence properties of the beam.
2. Plane mirror can image: Plane mirror can form an upright and equal virtual image.
For example, make-up with a flat mirror, try on clothes and shoes with a flat mirror, and check whether the dancers' movements are standardized with a flat mirror. Both a calm water surface and a smooth metal surface have the function of a plane mirror.
3. Periscope: Periscope is an example of using a flat mirror to change the direction of light.
The simplest periscope is to install a plane mirror at the upper corner and the lower corner of the pipeline. The two plane mirrors are parallel to each other and both make an angle of 45 with the horizontal direction. Tall objects shoot out horizontally and enter the observer's eyes, so that the objects blocked by the shelter can be seen from the periscope.
For example, dentists don't use flat mirrors, and laser levels uses flat mirrors to change the direction of light.
Three. spherical mirror
The spherical mirror comprises a convex mirror and a concave mirror; Convex mirror diverges parallel beams, and concave mirror converges parallel beams.
Car rearview mirror, street corner reflector; They are all convex mirrors, and the reflecting devices of flashlights, solar cookers and reflective astronomical telescopes are all equivalent to concave mirror.
1, convex mirror:
The convex mirror uses the outer surface of the spherical surface as the reflecting surface, so that a beam of parallel light is directed to the convex mirror and diverges after reflection.
Convex mirrors have the function of broadening the field of vision, and are often used as rearview mirrors of automobiles, reflectors on street corners, and stainless steel spoons in tableware. Their outer surfaces are convex mirrors.
2. concave mirror:
Concave mirror uses the interior of a sphere as a reflecting surface. Let the parallel beams shoot at concave mirror and converge after reflection.
Concave mirror is often used as the lamp bowl of stainless steel spoon in solar cookers, flashlights, car headlights, reflective binoculars and tableware, which is equivalent to concave mirror. From our daily observation, we find that concave mirror can become an upright and magnified virtual image. The mirror surface of the mirror consists of a convex mirror and a concave mirror. People's images are both enlarged and reduced, and they are uneven in fat and thin, which makes people laugh.
compare
Facial mirror
kind
flat mirror
spherical mirror
concave lens
convex mirror
Imaging principle
reflect
Influence on light
Neither convergent nor divergent.
Have a convergent effect
Have divergent function
Properties of images
Vertical, equal, virtual image
Upright, enlarged,
virtual image
Erection, reduction, virtual image
App application
Periscope, vanity mirror
Solar cooker,
Automobile headlight
The mirror at the corner of the rearview mirror.
essay question
1. Why do rearview mirrors on cars use convex mirrors instead of flat ones?
Answer: Because the viewing range from the convex mirror is large through the flat mirror with the same size, the convex mirror is used in the rearview mirror of the car, so that the driver can observe the objects in a large range behind the car from the mirror, which is beneficial to driving safety. A huge convex mirror is installed at the corner of the road, so that passing vehicles and pedestrians can see the traffic situation in a large area on the other side of the detour to avoid traffic accidents.