For the review materials of Physics 1~3 in 8th grade, Guangdong Province, you need to write them down completely, and don't talk nonsense. And history,

The first chapter "sound phenomenon" review overview.

First of all, the generation and spread of sound

1. Everything that makes a sound is vibrating. When you hold down the tuning fork, the pronunciation stops, which means the vibration stops and the sound stops.

Sound source of vibrating object.

☆ The chirping of cicadas is caused by the vibration of the vocal membrane when the vocal muscles of cicadas contract.

☆ Sprinkle some pieces of paper on the table, and it will jump when you knock on the table. It means that the table vibrates when it rings.

2. Sound transmission needs medium, and vacuum cannot transmit sound.

The fact that acoustic energy propagates in liquid: the fish in the water are scared away by the sound of people on the shore.

Experiment of sound energy transmission in liquid: put a proper amount of water in the sink, take two stones from the water with both hands and collide with each other. We can hear the crash.

3. The speed of sound propagation in the medium is simply called the speed of sound. The speed of sound is equal to the distance that sound travels every second. The speed of sound is related to the kind of medium and temperature.

Generally speaking, V is solid >: V liquid > V gas.

At 15℃, the speed of sound propagation in air is 340m/s or1224km/h..

☆ When running 100 meters in the sports meeting, the finish referee should record the time when he saw the gun smoking. If a gunshot is heard before recording, the recording time is later than the actual running time = 0.29 s (the air at that time was 15℃).

☆ Echo is formed when sound meets obstacles in the process of propagation. If the echo reaches the human ear more than 0. 1 S later than the original sound, the human ear can distinguish the echo from the original sound. At this time, the distance from the obstacle to the listener is at least 17m (at that time, the air was 15℃). Talking indoors sounds louder than in the wilderness, because the narrow space in the room leads to the echo reaching the human ear later than the original sound, less than 0. 1 S, and finally the echo and the original sound are mixed together to enhance the original sound.

☆ Ranging: Echo can be used to measure the seabed depth, iceberg distance and enemy submarine distance. In the measurement, we must first know the speed of sound propagation in seawater. The measurement method is: measure the time t from the sound emission to the reflection of the sound signal, and find out the propagation speed v of the sound in the medium, then the distance between the sound point and the object S= vt.

☆ Method of measuring the speed of sound: stand in the distance of a tall building and shout. Write down the time t from the call to the echo, and measure the distance s between the caller and the building. You can calculate the speed of sound velocity v in the air, v=.

Example: A classmate shouted at the bottom of a dry well. Three seconds later, he heard an echo. So how deep is this dry well? (The speed of sound is calculated at 340m/s)

Solution: v = 340/s

T = 3 seconds

S = vt =×340/s× ×3s = 5 10/0m.

Answer: The depth of dry well is about 5 10 meter.

P 16 solution to problem 2:

S = 1000 km

V sound = 1224 km/h v train = 200 km/h.

V aircraft = 600 km/h

T tone = S/V tone = ≈ 0.82h

T train = S/V train = = 5 hours

T plane = S/V plane = ≈1.67h.

A: It takes 0.82 hours for the sound to travel from Beijing to Shanghai.

It takes five hours for the train to travel.

The flight time of the plane is1.67 h.

Second, how do we hear the sound?

1. Transmission path of sound in the ear: The external sound causes the tympanic membrane to vibrate, which is transmitted to the auditory nerve through the ossicles and other tissues, and the auditory nerve transmits the signal to the brain, and people hear the sound.

2. Deafness: divided into nerve deafness and conductive deafness. The former cannot be cured, and the latter can be cured.

3. Bone conduction: Sound is transmitted to the auditory nerve through the skull and jaw, causing hearing. This mode of sound transmission is called bone conduction. Some people who have lost their hearing (conductive deafness) can hear sound in this way.

Binaural effect: (People have two ears, not one. ) The distance from the sound source to the two ears is generally different, and the characteristics such as the time and intensity when the sound reaches the two ears are also different. These differences are an important basis for judging the direction of sound source. This is the binaural effect.

Third, the characteristics of sound.

1. Music is the sound made when an object vibrates regularly.

2. Tone: refers to the level of voice. Tone is related to the vibration frequency of the vocal body. The higher the vibration frequency, the higher the pitch.

The number of times an object vibrates at 1s is called frequency. The faster the object vibrates, the higher the frequency.

The frequency unit is hertz.

Sound can be divided into infrasound, audible sound and ultrasonic wave.

Audible sound: the frequency is between 20 and 20~20000Hz.

Infrasound: The frequency is lower than 20Hz.

Ultrasonic: The frequency is higher than 20000 Hz.

Explain that bees can find flying by hearing, but why can't butterflies hear flying? (Bees' wings vibrate and sound, with a frequency of 20 ~ 20~20000Hz, which is within the hearing range of human ears; The vibration frequency of butterflies is lower than 20Hz, which is beyond the hearing range of human beings. )

Long air columns produce bass and short air columns produce treble. Musical instruments such as flute and Xiao vibrate through the air column when playing. The sound heard when pouring boiling water is related to the air column in the thermos.

3. Loudness: refers to the intensity (size) of sound.

When drumming, the scraps of paper scattered on the drum surface will jump, and the louder the drum sound, the higher the jump; When the sounding tuning fork touches the water surface, it can splash, and the louder the sound of the tuning fork, the greater the splash; The paper cone vibrates when the speaker sounds, and the louder the vibration, the louder the sound. According to the above phenomenon, it can be concluded that the loudness of sound is related to the amplitude of the object (the sounding body), and the greater the amplitude, the greater the loudness.

The main way to increase loudness is to reduce the divergence of sound. Like a doctor's stethoscope.

☆ The bass singer sings loudly, and the soprano sings softly for him: the soprano has a high and low loudness, and the bass has a low and high loudness.

4. timbre: it is related to the material structure of the vocal body. People can distinguish musical instruments or people according to their timbre.

5. Distinguish the three elements of musical sound: knowing people by hearing them-judging according to the timbre of different people; Shout loudly-refers to loudness; Tenor-refers to the tone.

Fourth, the harm and control of noise

1. Four major pollutions in contemporary society: noise pollution, water pollution, air pollution and solid waste pollution.

2. From the point of view of physics, noise refers to the sound produced when the vocal body vibrates irregularly.

From the perspective of environmental protection, noise refers to the sound that interferes with people's normal rest, study and work and interferes with the sound that people want to hear.

3. People use decibels (dB) to divide the sound level; Decibel measures the loudness of sound. The weakest sound that people can just hear (the lower hearing limit) is 0 decibel; In order to protect hearing, the noise should be controlled within 90dB；; In order to ensure work and study, the noise should be controlled within 70dB；; In order to ensure rest and sleep, the noise should be controlled within 50dB.

4. Noise reduction methods: noise reduction by sound source, propagation and human ear.

☆ When I want to take a lunch break at noon, the beautiful concert played at a high volume in my neighbor's house becomes noise.

Verb (abbreviation of verb) the use of sound

1. Examples of information that can be transmitted by sound:

A. use sonar technology to detect the depth of the seabed.

B. judge how far the thunder is.

C. the doctor examined the body with ultrasound.

Echo location-bats emit ultrasonic waves when flying, and these sound waves will be reflected back when they hit walls or insects. According to the location and arrival time of the echo, the bat can determine the location and distance of the target.

2. Examples of energy that can be transmitted by sound:

A. workers use ultrasonic to clean precision machinery such as clocks and watches.

B. the surgeon breaks the stone into fine powder with ultrasonic waves.

Chapter II Overview of Light Phenomenon

First of all, the spread of light

1. light source: an object that can emit light is called a light source.

The moon itself does not shine, it is not a light source.

Classification: natural light sources, such as the sun and fireflies;

Artificial light sources, such as bonfires, candles, oil lamps and electric lights.

2. Rule: Light travels in a straight line in the same uniform medium.

3. The application and phenomenon of linear propagation of light;

① Laser collimation. ② The formation of solar eclipse and lunar eclipse ③ Aim at the target when shooting.

④ Small hole imaging. A hole is an inverted real image, and the shape of the image has nothing to do with the shape of the hole. )

(5) The formation of shadows. When light encounters an opaque object during its propagation, it will form a black area behind the object, that is, a shadow. )

⑥ Arranged in columns. ⑦ The carpenter checks whether the battens are straight.

4. Light speed: In our calculation, the light speed in vacuum or air is taken as c = 3×108m/s = 3×105km/s ... The light speed in water is 3/4 of that in vacuum and 2/3 in glass.

Contrary to the speed of sound, light travels fastest in a vacuum. Generally speaking, V gas >; V liquid > v solid.

Second, the reflection of light.

1. Light reflection: When light is emitted from one medium to the surface of another medium, part of the light is reflected back to the original medium, which is called light reflection.

Light will be reflected when it touches the surface of any object.

2. The law of reflection: three lines are coplanar, the normal is centered, and the two angles are equal. That is, reflected light, incident light and normal are on the same plane; Reflected light and incident light are separated on both sides of the normal; The reflection angle is equal to the incident angle.

3. Reversibility of light path: In the phenomenon of light reflection, the light path is reversible.

4. Why can we see objects?

Because light enters our eyes. Divided into two situations:

(1) The object itself emits light (light source), and the light emitted directly enters our eyes;

(2) The object itself does not emit light because the surface of the object reflects the light emitted by other light sources and enters our eyes.

5. Specular reflection and diffuse reflection

⑴ Specular reflection: The parallel light incident on the surface of an object is still parallel after reflection.

Condition: The reflecting surface is smooth.

Application: looking at the calm water facing the sun, it is particularly bright. The blackboard "reflects light" and so on, all because of specular reflection.

⑵ Diffuse reflection: The parallel light incident on the surface of an object reflects in all directions.

Condition: The reflecting surface is uneven.

Application: You can see non-luminous objects from all directions, because light will diffuse when it hits an object. Put the desk in the middle of the classroom, because the light diffuses on the desk and we can see it from all directions. )

Every ray of specular and diffuse reflection obeys the law of light reflection.

Please illustrate the advantages and disadvantages of light reflection on people's lives with examples.

Advantages: use a flat mirror to observe the face in life; Most of the objects we can see enter our eyes because of the light reflected by the objects.

Advantages and disadvantages: the blackboard reflects light; Light pollution is caused by the reflection of glass curtain walls and glazed tile walls of high-rise buildings in cities.

Third, plane mirror imaging.

1. Imaging characteristics of flat mirror: equidistant, equidistant, vertical and virtual image. Namely:

① Images and objects are equal in size.

② The distance between the image and the object and the mirror is equal.

③ The line between the image and the object is perpendicular to the mirror.

The image of an object in a plane mirror is a virtual image. (Real image: the image formed by the actual light convergence point. Virtual image: an image formed by the convergence point of the reverse extension line of reflected light. )

Principle of plane mirror imaging: law of light reflection.

The function of plane mirror: imaging changes the light path.

2. Spherical mirror:

1) A mirror with the outer surface of a sphere as its reflecting surface is called a convex mirror.

The nature of convex mirror: convex mirror diverges light.

The image formed by convex mirror is a reduced virtual image. )

Convex mirror application: car rearview mirror, street corner to expand vision.

2) A mirror with the inner surface of a sphere as its reflecting surface is called a concave mirror.

Concave mirror will gather light. The reflected light from the focal point to concave mirror is parallel light.

Concave mirror applications: solar cookers, flashlights, car headlights.

☆ The dentist's endoscope is a flat mirror; The otolaryngologist's frontal mirror is concave mirror.

When studying the imaging characteristics of flat mirror, we often use flat glass, ruler and candle for experiments. The purpose of choosing two identical candles is to determine the imaging position and compare the size of the image and the object. The purpose of choosing flat glass instead of flat mirror is because flat glass is translucent and it is easy to see the image of candle.

Fourth, the refraction of light

1. Definition: When light obliquely enters another medium from one medium, the propagation direction is deflected; This phenomenon is called refraction of light.

2. The refraction law of light: three lines are in the same plane, the normal is in the middle, and the angle in the air is large. Namely:

(1) Refracted light, incident light and normal are in the same plane.

⑵ Refracted light and incident light are separated on both sides of the normal.

(3) When light is obliquely incident from air into water or other media, the refraction angle is smaller than the incident angle, and the refracted light is deflected to the normal direction.

When light obliquely enters another medium from one medium, the smaller the density, the greater the angle between light and normal. The air density is the smallest, and the included angle of light inside is the largest. Gas > liquid > solid

Light shoots vertically from air into water or other media, and its propagation direction remains unchanged (refraction angle = incident angle =0 degrees).

3. Reversibility of light path: In the refraction of light, the light path is reversible.

4. Application: When you look at the objects in the water from the air, or when you look at the objects in the air from the water, you see the virtual images of the objects, and the positions you see are higher than the actual positions.

☆ The reason why the pool water looks shallower than the actual water is because the light is refracted when it is obliquely incident into the air from the water, and the refraction angle is greater than the incident angle.

☆ Blue sky and white clouds form reflections in the lake, and fish in the water walk freely in the "clouds". The white clouds in the water we see here are virtual images formed by the reflection of light, and the fish we see are virtual images formed by the refraction of light.

Verb (abbreviation for verb) light scattering

1. dispersion: the phenomenon that a beam of sunlight passes through a glass prism and is decomposed into seven colors is called dispersion.

The composition of white light: red, orange, yellow, green, blue, indigo and purple.

2. A beam of sunlight shines on the red glass, only transmitting red light and absorbing light of other colors; A beam of sunlight on a red cardboard only reflects red light and absorbs light of other colors. A beam of sunlight shines on the blue glass, transmitting only blue light and absorbing other colors of light. A beam of sunlight on a blue cardboard only reflects blue light and absorbs light of other colors. This shows that:

Transparent objects only transmit light of the same color as it and absorb light of other colors;

Opaque objects only reflect light of the same color and absorb light of other colors.

That is to say: the color of a transparent object is determined by the color light that passes through it (what color light the object passes through is what color); The color of an opaque object is determined by the color light it reflects.

3. The three primary colors of colored light: red, green and blue. Mixing in equal proportion is white light.

The three primary colors of pigments: magenta, yellow and cyan. Mix them into black in the same proportion.

☆ The green light shines on the green spinach, which is green; According to the white paper, the white paper is green; When it shines on red paper, the red paper is black.

☆ White paper is printed in black, and everyone can see it clearly. Because white light shines on the test paper, white paper reflects white light into the eyes, and black words do not reflect light.

☆ If an object can reflect all colors of light, it appears white; If an object can absorb all colors of light, it appears black; If an object can transmit all colors of light, it is colorless and transparent.

6. Invisible light

1. spectrum: arranging seven colors of light in the order of red, orange, yellow, green, blue, indigo and purple is the spectrum.

2. infrared ray: it exists outside the red light in the spectrum and is invisible to the human eye.

Infrared ray has strong thermal effect and strong ability to penetrate clouds, and can be used for baking, remote control and taking pictures.

Infrared radiation to an object can heat the illuminated object; Generally, objects radiate infrared rays, and their ability to radiate infrared rays is related to the temperature of the object itself. The higher the temperature of an object, the stronger its ability to radiate infrared rays.

The principle of infrared night vision device is that human body temperature is higher than the surrounding vegetation or buildings at night, and the infrared radiation of human body is stronger than them.

3. Ultraviolet: It exists outside the violet light in the spectrum and is invisible to human eyes.

Ultraviolet rays have a strong chemical effect, which can be used to sterilize and promote bone growth, and can also be used for anti-counterfeiting by its fluorescence effect.

Sunlight is an important source of natural ultraviolet rays. Proper ultraviolet radiation is helpful to the synthesis of vitamin D, while too much ultraviolet radiation is harmful to human body.

Most of the ultraviolet rays in sunlight are absorbed by the ozone layer in the upper atmosphere and cannot reach the ground.

Chapter III Overview of Lenses and Their Applications

First of all, the lens

1. The propagation direction of light passing through the optical center remains unchanged.

2. The convex lens can make the light parallel to the main optical axis converge to the focal point (F).

3. The shorter the focal length of the convex lens, the stronger the convergence effect (the light is seriously deflected after passing through).

The convex lens with the same material, the more convex the surface, the shorter the focal length.

4. The convex lens can gather light; Concave lenses have a divergent effect on light.

5. Focus measurement:

(1) Aim the convex lens at the sunlight.

(2) Adjust the positions of the convex lens and the paper curtain until the smallest and brightest light spot appears on the paper curtain.

(3) The distance from the lens center to the light spot measured by the scale is the focal length.

Second, the lens in life

1. camera: the lens of the camera is equivalent to a convex lens, and the film in the camera box is equivalent to a light screen. When the object distance is more than twice the focal length, it can be inverted and reduced.

Projector: There is a lens equivalent to a convex lens on the projector. When the object distance is slightly larger than the focal length, it can be inverted and enlarged.

Magnifier: Magnifier itself is a convex lens with a short focal length. When the observed object is within its focal length range, it can form an upright and enlarged virtual image.

2. When the convex lens becomes a real image, the object and the real image are located on both sides of the convex lens respectively; When the convex lens forms a virtual image, the object and the virtual image are located on the same side of the convex lens respectively.

3. What are the similarities and differences between plane mirror imaging and convex lens forming virtual image?

Difference: a plane mirror is a virtual image of the same size produced by the reflection of light; A convex lens is a virtual image magnified by the refraction of light.

Similarity: all of them are formed by the intersection of opposite extension lines of light, which can not be accepted by the light curtain. And they are all upright.

Thirdly, explore the law of convex lens imaging.

1. In the experiment, the candle is lit so that the centers of the candle flame, convex lens and light screen are approximately at the same height. The purpose is to make the image of the candle flame in the center of the light curtain.

No matter how you move the screen in the experiment, you can't get an image on the screen. The possible reasons are as follows: ① candles are in focus; (2) candle flame focusing; ③ The centers of candle flame, convex lens and light screen are not at the same height; ④ The distance from the candle to the convex lens is slightly larger than the focal length, and the image is far away, so it is impossible to move the light screen of optical bench to this position.

2. The law of convex lens imaging

Double focal length is divided into virtual and real, and double focal length is divided into size, which is actually virtual and positive.

The object distance is equal to the image distance (u = v = 2f), forming an inverted and equal real image.

Camera: the object distance is greater than the image distance (u >；); 2f, f<v & lt2f), and become an inverted and reduced real image.

Projector: the object distance is less than the image distance (f

Magnifier: The object distance is within a focal length (U

3. Further understanding of the law:

⑴ u = f is the dividing point between real image and virtual image, positive image and inverted image, and the same side and different side of image.

⑵ u = 2f is the cut-off point for enlarging and reducing the real image.

(3) When the image distance is greater than the object distance, it becomes an enlarged real image (or virtual image), and when the image distance is less than the object distance, it becomes an inverted reduced real image.

(4) into a real image:

Four, eyes and glasses

1. imaging principle: the eyeball is like a camera. The light emitted by the object forms an inverted and reduced real image on the retina through the interaction between the lens and the cornea. The optic nerve cells distributed in the retina are stimulated by light, and this signal is transmitted to the brain, and we see objects.

2. The reason for myopia is that the lens is too thick, the refractive power is too strong, or the front and back direction of the eyeball is too long, so that the image is in front of the retina. Therefore, a concave lens should be placed in front of the eyes to make the image on the retina by its divergent effect on light.

3. The reason for hyperopia is that the lens is too thin, the refractive power is too weak, or the anterior-posterior direction of the eyeball is too short, and the light at the far point does not converge to one point and reach the retina. Therefore, a convex lens should be placed in front of the eyes, and the image can be imaged on the retina by using the characteristics that the convex lens can condense light.

4. The lens magnification is expressed by Ф, and f is the focal length, then Ф =.

Degree of spectacle lens t = × 100

The degree of convex lens (hyperopia lens) is positive; The power of concave lens (myopia lens) is negative.

5. Take a pair of reading glasses and measure the degrees of its two lenses.

Equipment: a white screen, a scale and a pair of reading glasses.

Steps:

(1) Face the two lenses to the sunlight respectively.

(2) Adjust the position of the convex lens until the smallest and brightest spots appear on the paper screen.

(3) Measure the distances f 1 and f2 from the lens to the light spot with a scale.

(4) Calculate the lens power with the formula. T = × 100。

Verb (abbreviation for verb) microscope and telescope

1. microscope: there are two groups of lenses at both ends of the microscope barrel, and each group of lenses is equivalent to a convex lens. The convex lens near the eyes is called eyepiece, and the convex lens near the observed object is called objective lens.

The light from the observed object passes through the objective lens and becomes an enlarged real image; The function of the eyepiece is to enlarge the image again. After these two magnifications, we can see small objects invisible to the naked eye.

(The microscope objective lens has a short focal length, while the eyepiece lens has a slightly larger focal length. )

2. Telescope: One kind of telescope is also composed of two groups of convex lenses. The goal of the telescope is to make distant objects become (reduced) real images near the focus; The eyepiece acts as a magnifying glass to enlarge the image. (The telescope has a long focal length of the objective lens and a short focal length of the eyepiece. )

3. The angle of view from the object to the eye is not only related to the size of the object itself, but also related to the distance from the object to the eye.

☆ Briefly describe three methods (approximate values) for measuring focal length.

Method 1: point the convex lens at the sunlight so that there is a small bright spot on the other side, and measure the distance from the spot to the convex lens, that is, the focal length;

Method 2: Use the convex lens as a magnifying glass, and read the words in the book through the magnifying glass. When the text is blurred, measure the distance from the text to the convex lens, that is, the focal length;

Method 3: use convex lens for imaging. When a clear and equal-length image is obtained on the screen, measure the distance from the object to the convex lens, and then divide it by 2 to get the focal length.

☆ Briefly describe several methods to distinguish convex lens from concave lens.

Method 1: Look at the appearance, the one with a thick middle and a thin edge is a convex lens, otherwise it is a concave lens.

Method 2: Look at the words in the textbook. It is a convex lens that can enlarge the words, otherwise it belongs to a concave lens.

Method 3: Facing the sunlight, the lens that can concentrate the sunlight is a convex lens, otherwise it is a concave lens.

Method 4: The lens that can make the candle become an inverted image on the light screen is a convex lens.

Method 5: Let a farsighted eye look at nearby objects through the lens, and the convex lens can see clearly.

So much for physics. Sorry, I am a science student in high school. I don't know where to find information about history, but when I was in junior high school, I did well in the history exam. The way I study history is to summarize the main points of each lesson in my notebook and take them out every day. It's best to take time as a clue, so it won't be chaotic.

But the learning methods vary from person to person. I was also told how to read English, but I always failed, so it's hard to say how to learn. What suits you is good.

I hope I can help you.