Junior high school physics notes

Review Outline for Chapter 1 "Sound Phenomenon"

1. The Occurrence and Propagation of Sound

1. Description of the phenomenon in Figure 1.1-1 of textbook P13: everything Objects that make sound vibrate. When you press the tuning fork for pronunciation with your hand, the pronunciation stops. This phenomenon means that the vibration stops and the sound stops. A vibrating object is called a sound source.

Practice: ① When people speak and sing, they rely on the vibration of their vocal cords. The melodious bird song relies on the vibration of the song membrane. The crisp cricket sound relies on the vibration of wing friction. Its vibration frequency must be 20- Between 20,000 times/second.

② In the lyrics of "Yellow River Cantata", "The wind is roaring, the horses are braying, and the Yellow River is roaring." The sound sources of "roar", "call" and "roar" here are air, horse, and Yellow River water.

③When you knock on the table, you hear the sound, but you cannot see the vibration of the table. What method can you think of to prove the vibration of the table? You can scatter some shredded paper on the table, which will bounce when you hit it.

2. The propagation of sound requires a medium, and sound cannot be transmitted in a vacuum. In the air, sound travels as invisible sound waves. The sound waves reach the human ear, causing the eardrum to vibrate, and the person hears the sound.

Exercise: ①P14 The experiment shown in Figure 1.1-4 can be concluded that sound cannot be transmitted in a vacuum, and there is no air on the moon, so the astronauts who landed on the moon had to rely on wireless phones to talk even if they were very close to each other. Because radio waves can also propagate in vacuum, the propagation speed of radio waves is 3×108 m/s.

② "The sound of wind, rain, and reading, the sound reaches the ears" explains: Gases, liquids, and solids can all make sound, and air can transmit sound.

3. The speed of sound propagation in the medium is referred to as the speed of sound. Under normal circumstances, v solid > v liquid > v gas. The propagation speed of sound in air at 15°C is 340m/s or 1224km/h, and the propagation speed in vacuum is 0m/s.

Exercise: ☆There is a section of steel pipe filled with water, length L, knock on one end, and hear 3 sounds on the other end. The order of transmission time from shortest to longest is

☆When running a 100-meter race at a sports meeting, the referee at the finish line should count the time when he sees the smoke from the gun. If you hear the gunshot and then record the time, the recorded time will be 0.29s later (earlier or later) than the actual running time (the air at that time is 15℃).

☆The following experiments and examples can illustrate the conditions for the generation or propagation of sound (①②④) ①Put some crushed foam on the drum surface. You can observe the constant beating of the crushed foam when beating the drum. ② When a mobile phone is placed in a vacuum cover, when there is an incoming call, only the indicator light flashes and no ringing sound is heard; ③ Take a piece of cardboard and let it slide across the teeth of the wooden comb, one time faster and the other slower. The two times are different; ④When the gong sounds, press the gong with your hand and the sound will stop.

4. Echo is formed when sound encounters obstacles and is reflected back during propagation. If the echo reaches the human ear more than 0.1s 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. Conversations in a house sound louder than in the wilderness. The reason is that the space in the house is relatively small, so the echo reaches the human ear less than 0.1s later than the original sound. Eventually, the echo and the original sound are mixed together to strengthen the original sound.

Use: The echo can be used to measure the depth of the seabed, the distance to icebergs, and the distance of enemy submarines. When measuring, you must first know the propagation speed of sound in seawater. The measurement method is: measure the time when the sound is emitted until it is reflected back. According to the time t of the sound signal, find the propagation speed v of sound in the medium, then the distance between the sounding point and the object is S=vt/2.

2. How do we hear sound

1. The way sound propagates in the ear: Sound from the outside causes the tympanic membrane to vibrate, and this vibration is transmitted through the auditory ossicles and other tissues. To the auditory nerve, the auditory nerve transmits the signal to the brain, and the person hears the sound.

2. Deafness: divided into neurological deafness and conductive deafness.

3. Bone conduction : Sound can be transmitted not only through the ears, but also through the skull and jaw to the auditory nerve, causing hearing. This method of sound conduction is called bone conduction. Some people who have lost their hearing can hear sounds this way.

4. Binaural effect: People have two ears instead of one. The distance from the sound source to the two ears is generally different, and the time, intensity and other characteristics of the sound reaching the two ears are also different. These differences are an important basis for judging the direction of the sound source. This is the binaural effect.

3. Musical sound and three characteristics

1. Musical sound is the sound emitted when an object vibrates regularly.

2. Pitch: the level of sound perceived by people. When you use a piece of cardboard to draw fast and slow strokes on the teeth of the comb, you can find that the faster strokes have a higher pitch. When you use the same force to move rubber bands of different thicknesses, you can find that the rubber bands vibrate and make sounds

< p> Turn it up. The most common conclusion you can get by combining the two experimental phenomena is that the pitch is related to the vibration frequency of the sound emitter. The higher the frequency, the higher the pitch; the lower the frequency, the lower the pitch. The number of times an object vibrates in 1 second is called frequency. The faster the object vibrates, the higher the frequency. The frequency unit is times/second and is also recorded as Hz.

Exercise: Explain that the flight of bees can be detected by hearing, but why the flight of butterflies cannot be heard? The vibration frequency of bees' wings is within the hearing range of the human ear, while the vibration frequency of butterflies is not within the hearing range.

3. Loudness: the size of sound perceived by the human ear. Loudness is related to the amplitude of the generator and the distance from the sound source. When an object vibrates, the maximum distance it deviates from its original position is called amplitude. The greater the amplitude, the greater the loudness. The main way to increase loudness is to reduce the divergence of sound.

Exercise: ☆The bass singer sings loudly, and the soprano sings softly for him: the soprano has a higher pitch and has a lower loudness, while the bass has a lower pitch and has a higher loudness.

☆When you beat the drum, the confetti scattered on the drum surface will beat, and the louder the drum sound, the higher the beat will be; if you touch the sounding tuning fork to the water, it will splash water, and the louder the sound of the tuning fork will splash. The larger the water splash; the paper cone will vibrate when the speaker produces sound, and the louder the sound vibration will be. Based on the above phenomena, it can be concluded that: ⑴ Sound is produced by the vibration of objects ⑵ The size of sound is related to the amplitude of the sound emitter.

4. Tone: determined by the object itself. People can identify musical instruments or distinguish people based on their timbre.

5. Distinguish the three elements of music: hearing the sound and knowing the person - judging based on the timbre of different people; shouting loudly - refers to the loudness; soprano singer - refers to the pitch.

4. Harm and control of noise

The four major pollutions in contemporary society: noise pollution, water pollution, air pollution, and solid waste pollution.

From the perspective of physics, noise refers to the sound emitted by the sound-emitting body making irregular and chaotic vibrations; from the perspective of environmental protection, noise refers to the sound that hinders people's normal rest, study and work, and is harmful to people's needs. The sound you listen to is a disturbing sound.

People use decibels (dB) to classify sound levels; the lower limit of hearing is 0dB; to protect hearing, the noise should be controlled not to exceed 90dB; to ensure work and study, the noise should be controlled not to exceed 70dB; to ensure rest and sleep, Control noise not to exceed 50dB.

Methods to reduce noise: reduce it at the sound source, reduce it during propagation, and reduce it at the human ear.

5. Utilization of Sound

Sound can be used to spread information and transfer energy

Review Outline for Chapter 2 "Light Phenomena"

1. Straight-line propagation of light

1. Light source: Definition: An object that can emit light is called a light source.

Category: Natural light sources, such as the sun, fireflies; artificial light sources, such as bonfires, candles, oil lamps, and electric lamps. The moon itself does not emit light; it is not a source of light.

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

3. Light is an ideal physical model established by abstracting a small beam of light. Establishing an ideal physical model is one of the common methods for studying physics.

Exercise: ☆Why can you see that the beam of light emitted from the car headlights is straight in foggy weather?

Answer: Light travels in straight lines in the air. During the propagation of light, part of the light encounters fog and is diffusely reflected, and enters the human eye. People can see the straight line propagation of light.

☆In the morning, the position of the sun that has just risen from the horizon is higher than its actual position. This phenomenon shows that light does not propagate in a straight line in a non-uniform medium.

4. Applications and phenomena:

① Laser alignment.

②The formation of shadow: During the propagation process of light, it encounters an opaque object and forms a black area or shadow behind the object.

③The formation of a solar eclipse and a lunar eclipse: A lunar eclipse can be formed when the earth is in the middle.

As shown in the picture: behind the moon

you can see the total solar eclipse at position 1

and the sun at position 2

Partial eclipse, look at position 3 to see an annular solar eclipse.

④ Small hole imaging: The small hole imaging experiment has been recorded in the "Mo Jing" as early as the "Mo Jing". The small hole is imaged into an inverted real image, and the shape of the image has nothing to do with the shape of the hole.

5. Speed ??of light:

The speed of light in vacuum is C=3×108m/s=3×105km/s; the speed of light in air is about 3×108m/s. The speed of light in water is 3/4 of the speed of light in vacuum, and the speed of light in glass is 2/3 of the speed in vacuum.

2. Reflection of light

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

2. Law of reflection: three lines are on the same plane, the normal is in the middle, the two angles are equal, and the light path is reversible. That is: the reflected light, the incident light, and the normal are on the same plane, and the reflected light and the incident light are separated by the normal On both sides of the line, the angle of reflection is equal to the angle of incidence. The optical path is reversible during the reflection of light.

3. Classification:

⑴ Specular reflection:

Definition: Parallel light incident on the object surface remains parallel after reflection

Condition: Reflective surface is smooth.

Application: Look at the calm water surface facing the sun, it is particularly bright. The "reflection" of the blackboard, etc., are all due to specular reflection

⑵ Diffuse reflection:

Definition: Parallel light incident on the object surface is reflected in different directions, each Light obeys the laws of light reflection.

Conditions: The reflective surface is uneven.

Application: Objects that do not emit light can be seen from all directions because the light hits the object and is diffusely reflected.

Exercise: ☆Please give an example to explain the advantages and disadvantages of light reflection on people's life and production.

⑴ Advantages: Use a plane mirror to observe faces in life; most of the objects we can see are due to the reflected light from the objects entering our eyes.

⑵Disadvantages: blackboards reflect light; reflections from glass curtain walls and glazed brick walls of tall buildings in the city cause light pollution.

☆Put the table in the middle of the classroom. We can see it from all directions. The reason is: light is diffusely reflected on the table.

4. Mask:

⑴Plane mirror:

Imaging characteristics: equal size, equal distance, vertical, virtual image

①Image , objects are of equal size

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

③The line connecting the image and the object is perpendicular to the mirror surface

④The virtual image formed by the object in the plane mirror.

Principle of imaging: reflection theorem of light

Function: imaging, changing the light path

Real image and virtual image: Real image: the image formed by the actual point of convergence of light rays

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Virtual image: The image formed by the convergence point of the reverse extension line of the reflected light

⑵Spherical mirror:

Definition: Use the inner surface of the sphere as the reflecting surface.

Properties: A concave mirror can converge the parallel light rays directed towards it at one point; the reflected light from the focus to the concave mirror is parallel light

Applications: solar cookers, flashlights, cars Headlight

Definition: Use the outer surface of a sphere as a reflective surface.

Properties: Convex mirrors diffuse light. The image formed by a convex mirror is a reduced virtual image

Application: Car rearview mirror

Exercise: ☆When studying the imaging characteristics of plane mirrors, we often use flat glass, rulers, and candles. In the experiment, the purpose of choosing two identical candles is to facilitate the determination of the position of the image and the comparison of the size of the image and the object.

☆ The glass in front of the driver of the car is not vertical, but tilted upward and inward. In addition to reducing the resistance encountered when moving forward, the advantage of doing so from an optical point of view is that it makes the inside of the car more comfortable. The image of the object is above the driver's line of sight and does not affect the driver's view of the road. Car headlights are installed under the front of the car: they can make obstacles in front of the car form longer shadows on the road, making it easier for drivers to detect them early.

3. Color and invisible light

1. The composition of white light: red, orange, yellow, green, blue, indigo, violet.

Colored light The three primary colors of pigments: red, green, and blue. The three primary colors of pigments: magenta, yellow, and cyan

2. Invisible light: infrared, ultraviolet rays

Chapter 3 "Lens and their Application》Review Outline

1. Refraction of Light

1. Definition: When light is incident obliquely from one medium into another medium, the direction of propagation generally changes; this phenomenon It is called the refraction of light.

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

⑴Refracted light, the incident light and the normal are in the same plane.

⑵The refracted ray and the incident ray are separated from both sides of the normal line.

⑶ When light is incident obliquely from air into water or other media, the refraction angle is smaller than the incident angle, which is near-normal refraction.

When light is incident obliquely into the air from water or other media, the refraction angle is greater than the incident angle, which is far normal refraction.

Light is incident vertically from air (or emitted from other media), and the refraction angle = incident angle = 0 degrees.

3. Application: When looking at an object in the water from the air, or looking at an object in the air from the water, you see a virtual image of the object, and the position you see is higher than the actual position

Practice :☆The reason why the pool water looks shallower than it actually is is because light is refracted when it is incident from the water to the air, and the refraction angle is greater than the incident angle.

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

2. Lens

Noun: thin lens: the thickness of the lens is much smaller than the radius of the sphere.

Principal optical axis: a straight line passing through the centers of two spheres.

Optical center: (O) is the center of the thin lens. Properties: The propagation direction of light passing through the optical center does not change.

Focus (F): A convex lens can make light rays parallel to the main optical axis converge at a point on the main optical axis. This point is called the focus.

Focal length (f): The distance from the focus to the optical center of the convex lens.

Typical optical path

Name Also known as glasses Real object

Shape Optics

Symbol Properties

Convex lens Converging lens Aging Mirror has a converging effect on light rays

Concave lens Divergent lens Myopic lens has a diverging effect on light rays

3. Fill in the form:

3. Convex lens imaging rules and its applications

1. Experiment: During the experiment, light the candle so that the centers of the candle flame, convex lens and light screen are roughly at the same height. The purpose is to make the image of the candle flame be in the center of the light screen.

If during the experiment, no matter how you move the light screen, you cannot get an image on the light screen, the possible reasons are: ① the candle is within the focus; ② the candle flame is at the focus; ③ the candle flame, convex lens, The centers of the light screens are not at the same height; ④ The distance from the candle to the convex lens is slightly greater than the focal length, and the image is formed in a very far place, and the light screen of the light bench cannot be moved to this position.

2. Experimental conclusion: (Convex lens imaging law)

F is divided into virtual and real, 2f size, real is inverted, virtual is positive,

For details, see the table below:

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Object distance Nature of image Image distance Application

Inverted, upright Zoom in, zoom out Virtual, real

u>2f Inverted zoom out Real image f

f2f Slide projector

uu Magnifying glass

3. For regular Further understanding:

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

⑵u=2f is the dividing point between image enlargement and reduction

⑶When the image distance is greater than the object distance, an enlarged real image (or virtual image) is formed. When the image distance is smaller than the object distance, an enlarged real image (or virtual image) is formed. An inverted, reduced real image.

⑷ When forming a real image:

⑸ When forming a virtual image:

4. Eyes and glasses

1. Imaging principle: From the object The emitted light passes through a comprehensive convex lens such as the lens and travels on the retina to form an inverted, reduced real image. The optic nerve cells distributed on the retina are stimulated by the light and transmit this signal to the brain, so that people can see the object.

2. Correction of myopia and hyperopia: Myopia should wear concave lenses, and hyperopia should wear convex lenses.

5. Microscope and telescope

1. Microscope: There is a set of lenses at both ends of the microscope barrel. Each set of lenses functions as a convex lens. The convex lens close to the eye is called the eyepiece, and the convex lens close to the object being observed is called the objective lens. The light from the object being observed passes through the objective lens and becomes a magnified real image, just like the lens of a projector. The eyepiece acts like an ordinary magnifying glass, magnifying the image again. After these two magnifications, we can see small objects invisible to the naked eye.

2. Telescope: There is a telescope also composed of two sets of convex lenses. The convex lens close to the eye is called the eyepiece, and the convex lens close to the object being observed is called the objective lens. Whether we can see an object clearly depends on the size of the "angle of view" formed by our eyes. Although the image formed by the objective lens of the telescope is smaller than the original object, it is very close to our eyes. Coupled with the magnifying effect of the eyepiece, the viewing angle can become very large.

Review Outline for Chapter 4 "Changes in State of Matter"

1. Temperature

Definition: Temperature represents the hot or cold degree of an object.

Units:

Thermodynamic temperature is used in the International System of Units.

The commonly used unit is degrees Celsius (℃). It is stipulated that under a standard atmospheric pressure, the temperature of the ice-water mixture is 0 degrees and the temperature of boiling water is 100 degrees. They are divided into 100 equal parts, and each equal part is called The temperature of 1 degree Celsius in a certain place -3 degrees Celsius is read as: minus 3 degrees Celsius or minus 3 degrees Celsius

Conversion relationship T=t + 273K

Measurement - Thermometer (commonly used liquid thermometer)

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① Thermometer structure: There is a glass bubble underneath, which contains mercury, kerosene, alcohol and other liquids; there is a thin glass tube with uniform thickness inside, and the scale is evenly engraved on the outer glass tube.

② The principle of a thermometer: it works by utilizing the thermal expansion and contraction of liquids.

③ Classification and comparison:

Classification Experimental thermometer, thermometer, thermometer

Uses: Measuring the temperature of objects, measuring room temperature, measuring body temperature

Range - 20℃～110℃ -30℃～50℃ 35℃～42℃

Graduation value 1℃ 1℃ 0.1℃

Liquid used Mercury kerosene (red) Alcohol (red) Mercury

Special structure, there is a constriction on the top of the glass bulb

Instructions for use Do not throw it away when using it, and do not leave the object when measuring the object to read. Shake it before use to leave the human body for reading

④ How to use commonly used thermometers:

Before use: observe its range to determine whether it is suitable for the temperature of the object to be measured; and recognize the graduation value of the thermometer for accurate readings.

When using: The glass bulb of the thermometer is completely immersed in the liquid to be measured, and do not touch the bottom or wall of the container; the glass bulb of the thermometer is immersed in the liquid to be measured and wait for a while, and then take a reading after the thermometer's indication is stable; when reading, the glass bulb should be Continue to stay in the liquid being measured, with your line of sight level with the upper surface of the liquid column in the thermometer.

Exercise: ◇The purpose of making the glass bulb of the thermometer larger is: when the temperature changes at the same time, the volume changes greatly. The purpose of making the glass tube above thin is: when the liquid volume changes at the same time, the liquid column changes greatly. The same purpose of this measure is: accurate readings.

2. Changes in the state of matter

Fill in the name of the change in the state of matter and the endothermic and exothermic conditions:

1. Melting and solidification

① Melting:

Definition: The change of an object from solid to liquid is called melting.

Crystalline substances: sea waves, ice, quartz crystal, amorphous substances: rosin, paraffin glass, asphalt, beeswax

Salt, alum, naphthalene, various metals

Melting image:

Melting characteristics: solid-liquid storage, absorbing heat, constant temperature. Melting characteristics: absorbing heat, first softening and thinning, and finally becoming liquid

The temperature keeps rising.

Melting point: The temperature at which a crystal melts.

Melting conditions: ⑴ Reach the melting point. ⑵ Continue to absorb heat.

Solidification:

Definition: The change of a substance from liquid to solid is called solidification.

Coagulation image:

Coagulation characteristics: solid-liquid storage, exothermic, constant temperature. Solidification characteristics: exothermic, gradually thickening, sticky, hardening, Finally

Freezing Point: The temperature at which a crystal melts. becomes a solid and the temperature continues to decrease.

The melting and freezing points of the same substance are the same.

Conditions for solidification: ⑴ Reach the freezing point. ⑵ Continue to release heat.

2. Vaporization and liquefaction:

① Vaporization:

Definition: The change of a substance from a liquid state to a gaseous state is called vaporization.

Definition: The vaporization phenomenon that can occur in a liquid at any temperature and only occurs on the surface of the liquid is called evaporation.

Influencing factors: ⑴The temperature of the liquid; ⑵The surface area of ??the liquid ⑶The flow of air on the surface of the liquid.

Function: evaporation, absorption of heat (absorbing heat from the outside world or its own), and has a cooling effect.

Definition: At a certain temperature, violent vaporization occurs simultaneously inside and on the surface of a liquid.

Boiling point: The temperature at which a liquid boils.

Boiling conditions: ⑴ Reach the boiling point. ⑵Continue to absorb heat

The relationship between boiling point and air pressure: The boiling point of all liquids decreases when the air pressure decreases and increases when the air pressure increases

Liquefaction: Definition: A substance changes from a gaseous state to a The liquid state is called liquefaction.

Methods: ⑴ Reduce the temperature; ⑵ Compress the volume.

Benefits: Reduced size for easier transportation.

Function: liquefaction releases heat

3. Sublimation and condensation:

①Sublimation definition: The process in which a substance changes directly from a solid state to a gaseous state, absorbing heat. Substances that easily sublimate include: iodine, ice, dry ice, camphor, and tungsten.

② Sublimation definition: the process of matter changing directly from gaseous state to solid state, releasing heat

Exercise: ☆ To make washed clothes dry as quickly as possible, please write four effective methods method.

⑴Expand the clothes to increase the contact area with the air. ⑵Hang clothes in a ventilated place. ⑶Hang the clothes in the sun or in a place with a high temperature. ⑷Dehydrate the clothes (wring them dry, spin them dry).

☆Explain "cold before frost, cold after snow"?

Cold before frost: Only when the outside temperature is low enough can the water vapor in the air release heat and condense into frost, so it is "cold before frost".

Cold after snow: Melting snow is a melting process and absorbs heat, so it is "cold after snow".