Echo distance measurement: 2s=vt
The first part: the generation and spread of sound.
One: the generation of sound
Key definitions:
1 Sound is produced by object vibration.
Vibration can produce sound.
Key points:
1 Everything that makes a sound vibrates.
Sound is produced by the vibration of objects.
When the vibration of the object stops, the occurrence also stops.
Doubt:
Everything that makes a sound is vibrating. Solids, liquids and gases can all make sounds due to vibration.
"When the vibration stops, it will happen and stop" is different from "When the vibration stops, it will happen and disappear". The vibration stopped, but there was no sound, but the original sound would still exist and continue to spread outward.
Two: the spread of sound
Key definitions:
1 The spread of sound needs media.
Sound travels in the form of waves, which is called sound waves.
Key points:
1 A substance that can transmit sound is called a medium.
The media of sound are: solid, gas and liquid.
Vacuum can't transmit sound.
Key points:
Sound travels outward in the form of waves. Due to the vibration of the object, the air on both sides of the object forms dense and alternating fluctuations and propagates far away. This is the sound wave.
Three: the speed of sound and echo
Key definitions:
The speed of sound propagation is described by the speed of sound, which is equal to the distance that sound travels every second. The speed of sound is related to the kind of medium and temperature.
Key points:
1 The distance that sound travels in a unit time is called the speed of sound.
The speed of sound is related to the type of medium. Generally speaking, it spreads fastest in solids, followed by liquids and slowest in gases.
The speed of sound is related to the controlled temperature. Generally speaking, in gas, the higher the temperature, the faster the speed of sound.
In the process of propagation, sound is reflected back after hitting an obstacle, so people can distinguish it from the original, so the reflected sound wave is an echo.
Key points:
At 15℃, the speed of sound propagation in air is 340m/s.
Expand:
1 conditions for distinguishing original sound from echo;
(1) The time when the bounce reaches the human ear is more than 0. 1s later than the original sound; ② The sound source is at least 17m away from the obstacle.
2 the role of echo:
① Strengthen the original sound; ② echolocation; ③ Echo ranging
3 echo distance measurement: 2s=vt
Part II: How do we hear the sound?
One: How to hear the sound?
Key definitions:
In the whole process of sound transmission to the brain, if any part is blocked, people will lose their hearing. However, if it is only a conduction obstacle, and people can find ways to transmit vibration to the auditory nerve through other channels, people can also perceive sound.
Key points:
1 Structure of human ear: external ear (auricle, external auditory canal), middle ear (tympanic membrane, ossicles) and internal ear (semicircular canal, vestibule, cochlea).
2 ways to hear sound: vibration of objects → medium → tympanic membrane or skull → auditory nerve → producing hearing.
Difficulties:
If the eardrum and ossicles that transmit sound are damaged, hearing will be reduced, which is called conductive deafness, but vibration can be transmitted to the auditory nerve through other ways, and people can continue to hear sound; If the cochlea, auditory pathway or nerves related to hearing are damaged, hearing will be reduced or even lost. This situation is called neurological deafness and generally cannot be cured.
Expand:
Conditions for hearing sound:
① The auditory system is normal; ② The vibration frequency of the object reaches the hearing range of human ears; (3) The sound has enough loudness; (4) There are media.
Two: bone conduction and binaural effect
Key definitions:
Sound passes through the skull, and the mandible can also penetrate the auditory nerve, causing hearing. In science, this way of sound transmission is called bone conduction.
Key points:
The way of bone conduction: object vibration → sound wave → skull or jaw bone → auditory nerve.
Key points:
Conditions of binaural effect:
① For the same sound, the intensity felt by both ears is different; ② For the same sound, both ears feel the same sound at different times; ③ For the same sound, the vibration steps of the two ear poles are different.
Section 3: Characteristics of Sound
One: Tone
Key definitions:
1 The faster the object vibrates, the higher the tone it emits; The slower the vibration, the lower the pitch.
2 The number of times per second that an object vibrates-frequency, which indicates the speed at which the object vibrates. Frequency determines the tone of sound. The unit of frequency is Hz, abbreviated as Hz, and the symbol is Hz.
3 the sound with frequency higher than 20000Hz is ultrasonic; The sound below 20Hz is infrasound.
Doubt:
1 Tone refers to the level of the sound, which is the thickness of the sound we usually say, not the size of the sound or the timbre of the sound.
Under the same medium and temperature, sounds with different frequencies travel at the same speed.
Expand:
What does pitch have to do with this?
Pitch is related to many factors, such as shape, size and properties of materials used.
Second: Loudness.
Key definitions:
1 The intensity of sound is called loudness.
In physics, amplitude is used to describe the amplitude of vibration of an object. The greater the amplitude of the object, the louder the sound produced.
Key points:
1 Loudness in physics refers to the strength of sound, which refers to the sound that people feel in life.
The loudness of objects perceived by human ears is related to the distance from the sound generator.
Key points:
The loudness of 1 is related to the amplitude of the sound source. The greater the amplitude, the greater the loudness. It has something to do with the distance between people and sound sources. The greater the distance, the smaller the loudness.
Tone and loudness are two fundamentally different characteristics, which are unrelated to each other.
Three: timbre
Key definitions:
The frequency of 1 determines the tone of the sound, and the amplitude determines the loudness of the sound.
Different vocal organs have different materials and structures and different timbres.
Key points:
Tone refers to the quality of sound, that is, tone quality.
Expand:
People's timbre will change with age, diet and health factors. Exercise can maintain a beautiful timbre.
Section 4: Harm and Control of Noise
One: the source of noise
Key definitions:
1 From a physical point of view, noise is the sound produced when the vocal body vibrates irregularly; From the perspective of environmental protection, all sounds that hinder people's normal rest, study and work, as well as those that interfere with people's desire to hear, belong to noise.
The waveform of noise is irregular and messy.
Difficulties:
The fundamental difference between musical sound and noise is that musical sound is produced by the regular vibration of the vocal body, and the waveform is regular; Noise is produced by the irregular vibration of the vocal body, and the waveform is chaotic.
Second, the classification of noise levels
Key definitions:
1 person takes decibel (symbol is dB) as the unit, indicating the level of sound intensity. Human hearing is 20 Hz-20000 Hz. 0dB: People can only hear the faintest sound. 30-40dB: Ideal quiet environment. In order to ensure rest and sleep, the sound should not exceed 50dB, in order to ensure work and study, the sound should not exceed 70dB, and in order to protect hearing, the sound should not exceed 90dB.
2 The three stages of sound from production to hearing:
(1) The vibration of the sound source produces sound; (2) the spread of air and other media; ③ Tympanic membrane vibration
Expand:
What are the hazards of noise?
The hazards of sound can be divided into physiological hazards, psychological hazards and physical hazards. Not too strong noise is boring; Strong noise makes people feel harsh and uncomfortable. After a long time, it will cause noise deafness, arrhythmia, elevated blood pressure, indigestion and other symptoms. Stronger noise will make people dizzy, sick and vomit in a few minutes, like seasickness; Strong noise will also affect the development of the fetus, hinder the intellectual development of children, and even directly cause human and animal deaths.
Three: Control noise
Key definitions:
Three aspects of noise control:
(1) to prevent noise; (2) blocking the spread of noise; (3) to prevent noise from entering the ear.
Key points:
Eliminate noise (from the sound source); Sound absorption (attenuation during propagation); Sound insulation (human ear attenuation)
Section 5: Use of Sound
One: Sound and information
Key points:
1 echolocation
2 sonar ranging, fishing.
Doubt:
The concept of sound is relatively broad, including ultrasound, infrasound and so on; Sound refers to the sound that people can feel.
Key points:
Sound can convey information.
Difficulties:
Ultrasound can accurately obtain the information of diseases in human body, which is called "B-ultrasound". When examining the body with ultrasonic waves, the structure of the internal organs of the human body can be clearly displayed on the screen by using computer image display equipment because of the different reflections of sound waves by various organs of the human body. Doctors can quickly find out the location of the lesion according to the image, and ultrasonic exploration is harmless to human body. This is different from "x-ray"
Two: sound and energy
Key points:
The vibration of an object → generating sound waves → transmitting energy → sound waves can transmit energy.
Key points:
Ultrasonic can be used to clean precision machinery; Surgeons can use ultrasonic vibration to remove stones from the human body.
Chapter II Basic knowledge of light phenomenon
1. light source: an object that can emit light by itself. The sun is a natural light source, while electric lamps and candle flames are artificial light sources. The moon and all the stars are not light sources.
2. Light propagates in a straight line in the same uniform medium. It can explain the shadow formation and pinhole imaging.
3. The speed of light in vacuum is the fastest in the universe, represented by the letter C: c=3× 108 m/s The speed of light in water is about 3/4 of that in vacuum.
The speed of light in glass is two-thirds of that in vacuum.
When light meets the surface of water, glass and many other objects, it will be reflected. The reflection of light follows the law of reflection. (1) The reflected light, incident light and normal line are in the same plane (2) The reflection angles of the reflected light and incident light on both sides of the normal line (3) are equal to the incident angle.
5. In the reflection phenomenon, the light path is reversible. Reflection is divided into specular reflection and diffuse reflection. Specular reflection: the surface is smooth, parallel light is incident, and the reflected light is still parallel. Diffuse reflection: the surface is rough, parallel light is incident, and light is reflected in all directions.
6. When light obliquely enters another medium from one medium, the propagation direction is deflected, which is called light refraction. When refraction occurs, emission must also occur. The optical path in refraction is also reversible.
7. When light is obliquely incident from air into water or other media, the refracted light will be deflected to the normal direction. The law of refraction of light: three lines * * * plane, two lines are divided into two sides, and the two angles are not equal (the angle is larger in air). Refraction phenomenon: pen dislocation, shallow pool, fish in the water, mirage, etc.
8. The phenomenon that a beam of white light (sunlight) is decomposed into seven colors of red, orange, yellow, green, indigo and purple through a prism is called optical dispersion. It shows that white light is not monochromatic light, but synthetic light composed of various monochromatic lights. Rainbow is the scattering of sunlight by water droplets.
9. The three primary colors of light: red, green and blue pigments: the colors of cyan, yellow and magenta transparent objects are determined by their colored light, and the colors of opaque objects are determined by their reflected colored light.
10, infrared rays are located outside the red light, and all objects are constantly emitting infrared rays. The higher the temperature of an object, the more infrared rays it radiates, and the object is also absorbing infrared rays. Infrared action:
① Thermal action: heating food thermogram for diagnosis ② Infrared remote sensing: earth survey, water source search, forest fire monitoring, etc. ③ Remote control: TV, air conditioner, etc.
1 1. Ultraviolet rays are located outside the violet light, and sunlight is an important source of natural ultraviolet rays. Ozone can absorb ultraviolet rays and avoid the harm of excessive ultraviolet rays to human body. The function of ultraviolet ray: ① sterilization: ultraviolet lamp in hospital ② fluorescence function of ultraviolet ray: money detector and anti-counterfeiting; ③ Proper ultraviolet irradiation is beneficial to the synthesis of vitamin D, the absorption of calcium and the growth and health of human bones.
Chapter III Lenses and Their Applications
1. A lens with a thick middle and a thin edge is called a convex lens, and a lens with a thick edge and a thin middle is called a concave lens. Light passing through the optical center will not change its propagation direction.
2. A convex lens has two real focal points, and the distance from the focal point to the optical center is called the focal length. A concave lens has two virtual focal points.
3. Convex lens can condense light, while concave lens can diverge light.
4. Three kinds of special light: ① The light passing through the optical center does not change its propagation direction. ② The light parallel to the main optical axis passes through the focal point after refraction. For concave lens, its focus is virtual focus, which is the reverse extension line of refracted light. ③ The refracted light passing through the focal point is parallel to the main optical axis. For concave lens, it is virtual focus, which is the forward extension line of incident light passing through the focus.
5. The lens of the camera is a convex lens, and the function of the focusing ring is to adjust the distance between the lens and the film. When shooting close-up, the lens stretches forward.
When shooting a distant view, the lens retracts, the aperture controls the amount of light, and the shutter controls the exposure time.
6.
U & gt2f Inverted Miniature Reality Camera
U=2f handstand equals reality.
F<u & lt2f Inverted Amplification Real Projector
U=f is not like a picture.
U<f vertical magnifying virtual magnifying glass
Dual focal length is divided into virtual and real, dual focal length is divided into size, and real and virtual are used for imaging. The size and distance of the image are fixed, and the image runs with the object.
7. The eye is like a camera, the lens is equivalent to a convex lens, and the retina is equivalent to a light screen. The apparent distance is 25cm. Hyperopia can see distant objects clearly, but can't see near ones clearly. The lens is too thin and imaged behind the retina. Myopia can see the near objects clearly, but can't see the distant objects clearly. The lens is too thick and imaged in front of the retina.
8. There should be concave lenses for myopia and convex lenses for hyperopia. Glasses power = 100× power = 1/f
9. The eyepiece and objective lens of a telescope are convex lenses, the eyepiece is equivalent to a magnifying glass, and the objective lens is equivalent to a camera lens. The eyepiece and objective lens of a microscope are also convex lenses, the eyepiece is equivalent to a magnifying glass, and the objective lens is equivalent to a projection lens.