Chapter 1 Sound Phenomenon

1. Production of Sound:

1. Sound is produced by the vibration of objects; (people make sounds by vibrating their vocal cords, Bees make sounds by vibrating small black dots under their wings, wind sounds are made by vibrating air, wind instruments make sounds by vibrating air columns, string instruments make sounds by vibrating strings, drums make sounds by vibrating drum heads, bells make sounds by vibrating bells, etc.);

2. The vibration stops and the occurrence stops; but the sound does not disappear immediately (because the original sound continues to propagate);

3. The sound emitter can be solid, liquid and Gas;

4. The vibration of sound can be recorded and restored (record production and playback);

2. Propagation of sound

1 , The propagation of sound requires a medium; solids, liquids and gases can all propagate sound; when sound propagates in solids, it loses the least (it propagates furthest in solids, and rails propagate sound). In general, sound propagates furthest in solids. Fast, the slowest among gases (except cork);

2. Sound cannot be transmitted in a vacuum, and astronauts on the moon (in space) can only talk through wireless phones;

3. Sound propagates in the form of waves (sound waves);

Note: The sound object must vibrate, and the sound may not be heard if there is vibration;

4. Speed ??of sound: the object propagates per second The distance is called the speed of sound, and the unit is m/s; the calculation formula for the speed of sound is v=; the speed of sound in the air is 340m/s;

3. Echo: During the propagation of sound, it encounters The obstacle is reflected back and then transmitted to the human ear. The human ear hears the reflected sound called echo (such as: the echo of the mountains, the thunder in the summer, the echo wall of the Temple of Heaven in Beijing)

1. Conditions for hearing echo: The time interval between the original sound and the echo is more than 0.1s (the echo of the teacher's words cannot be heard in the teacher's room. The sound in the small room becomes louder because the original sound and the echo overlap);

2. Utilization of echo: measuring distance (distance from car to mountain, sea depth, glacier to ship);

4. How to hear sound

1. The structure of the human ear: The human ear is mainly composed of the external auditory canal, tympanic membrane, auditory ossicles, cochlea and auditory nerve;

2. Sound is transmitted into the ear canal, causing the tympanic membrane to vibrate, and then transmitted to the brain through the auditory ossicles and auditory nerve to form hearing;

3. If there is any obstacle in the process of transmitting sound to the brain, people will lose hearing (obstacles in the tympanic membrane and auditory ossicles are conductive deafness; obstacles in the auditory nerve are neurological deafness);

4. Bone conduction: Without the help of the eardrum, it is transmitted to the auditory nerve by the skull and jaw, and then to the brain to form hearing (Beethoven listened to music after being deaf, and we hear our own voice when we speak) ;The performance of bone conduction is better than that of air sound transmission;

5. Binaural effect: The distance from the source to the two ears is generally different, so the time, intensity and pace of sound reaching the two ears Also different, the phenomenon of the direction of the sound source can be judged from this (hearing stereo sound);

5. The characteristics of sound include: pitch, loudness, and timbre;

1. Pitch: the level of the sound It is called pitch. The higher the frequency, the higher the pitch (frequency: the number of times an object vibrates per second, indicating how fast the object vibrates. The unit is Hertz. The larger the vibrating object, the lower the pitch;)

2. Loudness: The strength of the sound is called loudness; the greater the amplitude of the object, the stronger the loudness; the farther the listener is from the sounder, the weaker the loudness;

3. Timbre: Although the pitch and loudness of different objects They may all be the same, but the timbre must be different; (identifying the sound of an object depends on the timbre)

Note: pitch, loudness, and timbre do not affect each other and are independent of each other;

6. Ultrasonic waves and infrasound waves

1. The frequency of sound felt by the human ear has a range: 20Hz ~ 20000Hz, higher than 20000Hz is called ultrasonic wave; lower than 20Hz is called infrasound wave;

2 The hearing range of animals is different from that of humans. Elephants rely on infrasound waves to communicate.

Currents, earthquakes, volcanic eruptions, typhoons, and tsunamis all produce infrasound waves;

7. Harm and control of noise

1. Noise: (!) From a physical perspective, objects do The sound emitted by irregular vibrations is called noise; (2) From an environmental protection point of view, any sound that hinders people's normal study, work, and rest, as well as any sound that interferes with the sounds that people want to listen to, is noise;

2. Musical sound: From a physical point of view, the sound emitted by objects vibrating regularly;

3. Common sources of enrollment: the roar of airplanes, car horns, firecrackers, metal The friction sound between them;

4. Noise level: The unit that indicates the strength of the sound is decibels. Symbol dB, exceeding 90dB will harm health; 0dB refers to the sound that can just be heard by human ears;

5. Control noise: (1) Weak at the source (install a muffler); (2) During the propagation process (Planting trees. Soundproof walls) (3) Attenuating at the human ear (wearing earplugs)

8. Utilization of sound

1. Ultrasonic waves have large energy and high frequency and are used to Stones, cleaning clocks and other precision instruments; ultrasonic waves basically propagate along straight lines and are used for echolocation (bat direction identification) production (sonar system)

2. Transmitting information (doctors' "smell" when checking diseases, playing B-ultrasound, knock on the rails to listen to the sound, etc.)

3. Sound can transmit energy (the glass on the side of the airport was shattered, you cannot speak loudly in the snowy mountains, one tuning fork vibrates, and the untouched tuning fork vibrates (occurrence)

Chapter 2 Propagation of Light

1. Light source: An object that can emit light is called a light source. Light sources can be divided into 1. cold light sources (jellyfish, energy-saving lamps), hot light sources (torches, sun); 2. natural light sources (jellyfish, sun), artificial light sources (bulbs, torches); 3. biological light sources (jellyfish, hatchet fish) ), non-biological light sources (sun, light bulbs)

2. Propagation of light

1. Light propagates in straight lines in the same uniform medium;

2 , Application of linear propagation of light:

(1) Small hole imaging: The shape of the image has nothing to do with the shape of the small hole, it is like an inverted real image (the light spot under the shade of the tree is the image of the sun)

(2) Take a straight line: laser collimation (tunneling and orientation); gather the whole team; shoot and aim;

(3) Limit the line of sight: sit in a well and look at the sky (requires being able to make frogs with and without water) The light path diagram of the field of vision); a leaf blinds the eye;

(4) The formation of shadows: shadow; solar eclipse, lunar eclipse (requires knowing that the moon is in the middle during a solar eclipse; the earth is in the middle during a lunar eclipse)

3. Light: A straight line with an arrow is often used to represent the path and direction of light;

3. Speed ??of light

1. The speed of light in a vacuum is the fastest in the universe Speed;

2. In calculations, the speed of light in vacuum or air is c=3×108m/s;

3. The speed of light in water is about c, and the speed of light in glass is The speed is about c;

4. Light year: It is the distance that light travels in one year, and light year is the unit of length; 1 light year ≈ 9.46×1015m;

Note : Sound travels fastest in solids, second in liquids, slowest in gases, and does not travel in vacuum; light travels fastest in vacuum, second in air, and slowest in transparent liquids and solids (the two are exactly the same) on the contrary). The speed of light is much greater than the speed of sound (for example, if you see lightning first and then hear thunder, the time it takes for sound to travel during a 100m race cannot be ignored, but the time it takes for light to travel is negligible).

4. Reflection of light:

1. When light hits the surface of an object, part of the light will be reflected back by the object. This phenomenon is called reflection of light.

2. We see non-luminous objects because the light reflected by the objects enters our eyes.

3. The law of reflection: In the reflection phenomenon, the reflected light, incident light, and normal are all in the same plane; the reflected light and the incident light are separated on both sides of the normal; the reflection angle is equal to the incident angle.

(1). Normal line: the straight line perpendicular to the reflective surface drawn by the incident point of the light;

(2) Incident angle: the angle between the incident light ray and the normal line; Reflection angle: The angle between the normal ray and the normal line. (The incident light and the mirror form an angle θ, the incident angle is 90°-θ, and the reflection angle is 90°-θ)

(3) There is a causal relationship between the incident angle and the reflection angle, and the reflection angle is always It changes with the change of the incident angle, so it can only be said that the reflection angle is equal to the incident angle, but it cannot be said that the incident angle is equal to the reflection angle. (The mirror rotates θ, and the reflected light rotates 2θ)

(4) When the incident is vertical, what are the incident angle and reflection angle? Answer: At vertical incidence, the angle of incidence is 0 degrees, and the angle of reflection is also equal to 0 degrees.

4. In the phenomenon of reflection, the light path is reversible (look at each other's eyes)

5. Use the law of reflection of light to draw a general light path diagram (required to be able to draw):

(1) Determine the incident (reflection) point: The intersection of the incident ray and the reflective surface or the reflected ray and the reflective surface or the incident ray and the reflected ray is the incident (reflection) point

( 2) Draw a normal line based on the normal line being perpendicular to the reflecting surface.

(3). Draw the incident ray or reflected ray according to the reflection angle equal to the incident angle.

5. Two types of reflection: specular reflection and diffuse reflection.

(1) Specular reflection: When parallel light strikes a smooth reflective surface, the reflected light is still reflected parallelly;

(2) Diffuse reflection: When parallel light strikes On a rough reflective surface, the reflected light will be reflected in all directions;

(3) The similarities between specular reflection and diffuse reflection: both are reflection phenomena and both obey the law of reflection; the difference is: reflective surface Different (one smooth, one rough), the incident light in one direction, the reflected light reflected by the specular surface only shoots in one direction (dazzling); while the diffuse reflection shoots in all directions; (on a rainy day, walk towards the light and into the dark, and walk towards the backlight) In bright places, specular reflection occurs due to accumulated water, and diffuse reflection occurs on the ground. The movie screen is rough, and the blackboard is rough because diffuse reflection is used to shoot the light in all directions. The "reflection" on the blackboard is specular reflection.)

5. Plane mirror imaging

1. Characteristics of plane mirror imaging: virtual image, image and object are symmetrical about the mirror (the size of the image and the object are equal, the line connecting the corresponding points of the image and the object is perpendicular to the mirror surface, to the mirror surface The distance is equal; the image is the same up and down as the object, and the left and right are opposite (the left hand of the person in the mirror is the right hand of the person. When looking at the clock in the mirror, you need to look at the reverse side of the paper. The size of the image does not change when the object is far away or close to the mirror, but it also needs to be With the same distance away from and closer to the mirror, it is twice the distance to people)

2. The reason for the formation of reflection in the water: The calm water surface is like a plane mirror, which can form an image (the moon and the mirror in the water). (medium flower); for every point of the object, the image point it forms in the water is "equidistant" from the object point. The distance between each point on trees and houses and the water surface is different. The closer the point to the water surface, the more the image will be The closer it is to the water surface, the image composed of countless points will be reflected on the water surface (how high the object is from the water surface is how far the image is from the water surface, regardless of the depth of the water)

3. Plane mirror. The reason for the virtual image: the light rays reflected by the object on the plane mirror do not converge and diverge. The reverse extension lines of these rays (dotted lines are used when drawing) intersect to form an image that cannot be displayed on the light screen. , can only be observed through the human eye, so it is called a virtual image (not formed by the convergence of actual light rays)

Note: The light entering the eye does not come from the image point, but is reflected light.

It is required to be able to use the law of plane mirror imaging (the image and the object are symmetrical about the mirror) and the principle of plane mirror imaging (after the light emitted from the same object point is reflected, the reverse extension line of the reflected light intersects the image point) to make a light path diagram (make an object, image, reflected light and incident light);

6. Convex mirror and concave mirror

1. The outer surface of the ball is called a convex mirror, and the inner surface of the ball is the reflecting surface. Reflective surfaces are called concave mirrors;

2. Convex mirrors have a divergent effect on light and can increase the field of view (rear view mirrors on cars); concave mirrors have a convergent effect on light (solar cookers, which use light paths Reversible production of flashlight)

7. Refraction of light

1. When light is incident obliquely from one medium into another medium, the direction of propagation is deflected.

2. Light propagates in the same medium. When the medium is uneven, the direction of light propagation will also change.

3. Refraction angle: the angle between the refracted ray and the normal.

8. The law of refraction of light

1. In the refraction of light, the three lines are in the plane, and the normal line is in the center.

2. When light enters water or other media obliquely from air, the refracted ray is deflected toward the normal; when light enters air obliquely from water or other media, the refracted ray moves away from the normal (requires the ability to draw refraction) Light path diagram of light and incident light)

3. When the angle is oblique, the angle in the air is always larger; when the angle is vertically incident, the refraction angle and the incident angle are both equal to 0°, and the propagation direction of the light does not change

4. The refraction angle increases with the increase of the incident angle

5. When light hits the interface between two media, reflection and refraction occur simultaneously

6. The optical path in the refraction of light is reversible.

9. The phenomenon of refraction of light and its applications

1. Examples related to the refraction of light in life: The position of the fish in the water looks higher than the actual position (the actual position of the fish (behind and below where you see it); due to the refraction of light, the water in the pool looks shallower than it actually is; people in the water see the scenery on the shore at a higher position than the actual position; in summer, the position of the stars in the sky when seen is higher than the actual position of the stars Higher; looking at the pen through thick glass, the penholder seems to be misplaced; the chopsticks placed diagonally in the water seem to be bent upward; (requires the ability to make light path diagrams)

2. People use the refraction of light to see in the water The image of an object is a virtual image (the intersection of the reverse extension lines of refracted light)

10. Dispersion of light:

1. After the sunlight passes through the prism, it is decomposed into red and orange in turn. There are seven colors: yellow, green, blue, indigo, and violet. This phenomenon is called dispersion;

2. White light is complex color light mixed with various colors;

3. The rainbow in the sky is the dispersion phenomenon of light;

4. The three primary colors of colored light are: red, green, and blue; other colored lights can be mixed from these three colored lights, and white light is made of red, green, and blue colored lights. It is mixed; there is no black light in the world; the three primary colors of pigments are magenta, cyan, and yellow, and the mixture of the three primary colors is black;

5. The color of a transparent body is determined by the color light it transmits (what color is transparent What color of light passes through); the color of an opaque body is determined by the color of light it reflects (what color reflects what color of light, absorbs light of other colors, white objects emit light of all colors, black absorbs light of all colors)

Example: A red horse, green grass, red flowers, and black stones are drawn on a piece of white paper. Now when you look at the painting with green light in a darkroom, you will see a black horse and black stones. There are also black flowers on green paper, and the grass cannot be seen (grass and paper are both green)

11. Invisible light:

Sun spectrum: red, orange The seven colors of light, yellow, green, blue, indigo, and violet, arranged in order, are the solar spectrum;

(From left to right, the wavelength gradually decreases; the scattering gradually increases; the human eye's resolution decreases successively ) Application: The sun in the evening is red, the sky is blue on a sunny day, and the fog lights of cars are yellow.

Infrared rays: Infrared rays are located outside of red light and are invisible to the human eye;

All objects can emit infrared rays. The higher the temperature, the more infrared rays are radiated; (night vision goggles for contact )

Infrared rays have strong ability to penetrate clouds and fog (remote control detection)

The main performance of infrared rays is strong thermal effect; (heating)

Ultraviolet: in the spectrum It is located outside the purple light and is invisible to the human eye;

The main characteristic of ultraviolet light is its strong chemical effect; (disinfection, sterilization)

The physiological effect of ultraviolet light promotes the synthesis of vitamin D in the human body (more children Sunbathing), but excessive ultraviolet rays are harmful to the human body (ozone can absorb ultraviolet rays, we must protect the ozone layer)

Fluorescence effect; (money detection)

The natural ultraviolet rays on the earth come from the sun , the ozone layer blocks ultraviolet rays from entering the earth;

Chapter 3 Lenses and their Applications

1. Lens, a transparent glass element with at least one surface that is part of a sphere (required to be able to identify)

1. Convex lens, a lens that is thick in the middle and thin at the edge, such as: far-sighted lenses, camera lenses, projector lenses, magnifying glasses, etc.;

2. Concave lens, thin in the middle, Lenses with thick edges, such as myopia lenses;

2. Basic concepts:

1. The main optical axis: the straight line passing through the centers of the two spherical surfaces of the lens, represented by CC/;

2. Optical center: always located at the geometric center of the lens; represented by "O".

3. Focus: The light rays parallel to the main optical axis of the convex lens converge at a point on the main optical axis after passing through the convex lens. This point is called the focus; represented by "F".

4. Focal length: The distance from the focus to the optical center (usually because the lens is thick, the distance from the focus to the lens is approximately equal to the focal length). The focal length is represented by "f". As shown below:

Note: Both convex lenses and concave lenses have two focus points. The focus of the convex lens is the real focus, and the focus of the concave lens is the virtual focus;

Three special rays (requirements Can draw):

1. The propagation direction of the light passing through the optical center does not change after passing through the lens, as shown below:

2. The light passing through the main optical axis passes through the convex lens Focus; after passing through the concave lens, it diverges outward, but its reverse extension line must pass through the focus (so the convex lens has a convergence effect on the light, and the concave lens has a divergence effect on the light) as shown below:

3. The light passing through the focus of the convex lens The light rays are parallel to the main optical axis after passing through the convex lens; the light rays directed to the focus on the opposite side are parallel to the main optical axis after passing through the concave lens; as shown below:

4. How to roughly measure the focal length of a convex lens: Make the convex lens face the sun Light (sunlight is parallel light, so that the sunlight is parallel to the main optical axis of the convex lens), put a piece of white paper underneath, adjust the distance from the convex lens to the white paper until the light spot on the white paper is the smallest and brightest, and then use a scale Measuring the distance from the convex lens to the center of the light spot on the white paper is the focal length of the convex lens.

5. How to distinguish convex lenses and concave lenses:

1. Touch the lens with your hand. The thicker lens in the middle and thinner edges is a convex lens; the thinner lens in the middle and thicker edges is a concave lens.

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2. Let the lens face the sun and move the lens. The lens that can see smaller and brighter spots on the paper is a convex lens, otherwise it is a concave lens;

3. Use the lens to read words , what can magnify words is a convex lens, what can make words shrink is a concave lens;

VI. Camera: 1. The lens is a convex lens; 2. The distance from the object to the lens (object distance) is greater than twice the focal length, forming It is an inverted, reduced real image;

Projector: 1. The lens of the projector is a convex lens; 2. The function of the plane mirror of the projector is to change the direction of light propagation;

Note: To make the image larger in a camera or projector, the lens should be close to the object and away from the film and screen.

3. The distance between the object and the lens (object distance) is less than twice the focal length and greater than one time the focal length, resulting in an inverted, enlarged real image;

8. Magnifying glass: 1. The magnifying glass is a convex lens; 2. The distance between the magnifying glass and the object (object distance) is less than one focal length, and the resulting image is an enlarged, upright virtual image; Note: To make the object larger, the magnifying glass should be moved away from the object;

Explore the imaging rules of convex lenses: Equipment: convex lens, light screen, candle, light bench (with scale)

Notes: "Three-centre ***line": the flame center of the candle, the center of the lens The optical center and the center of the optical screen are on the same straight line; also called "three centers of equal height"

The rules of convex lens imaging (required to memorize and understand):

Imaging conditions Distance (u) Nature of imaging Image distance (v) Application

U>2f Inverted, reduced real image F

U=2f Inverted, equal-sized real image v=2f

F2f projector

U=f does not image

0f magnifying glass

Rule of thumb: the first focal point divides the virtual and the real, and the second focal point divides the big and small; the virtual image is upright on the same side, and the real image is inverted on the opposite side; the real image is small when the object is far away, and the virtual image is large.

Note: 1. The real image is formed by the convergence of actual light rays, which can be displayed on the light screen and can be viewed directly with the eyes. All light rays must pass through the image point;

2. The virtual image cannot Presented on a light screen, but can be seen with the eyes, it is formed by the convergence of reverse extension lines of light;

Note: a concave lens always forms a reduced, upright virtual image;

10 1. The lens of the eye is equivalent to a convex lens, and the retina is equivalent to a light screen (film);

12. Myopic eyes cannot see distant objects clearly. Distant objects are imaged in front of the retina, and the lens curvature is too high. If it is too large, you need to wear a concave lens to adjust;

13. Hyperopia cannot see nearby objects clearly. Near objects are imaged behind the retina. If the curvature of the lens is too small, you need to wear a convex lens to adjust;

Microscope and Telescope

14. A microscope is composed of an eyepiece and an objective lens. The objective lens and eyepiece are both convex lenses, which magnify the object twice;

15. A telescope is composed of It consists of an eyepiece and an objective lens. The objective lens makes the object become a reduced or inverted real image. The eyepiece is equivalent to a magnifying glass and forms a magnified image;

Chapter 4 Changes in the State of Matter

1. Temperature:

Temperature: Temperature is a physical quantity used to express the degree of hotness or coldness of an object;

Note: We say that a hot object has a high temperature, and a cold object has a low temperature. If If two objects are equally hot or cold, their temperatures will also be the same; it is generally unreliable to judge the hot or cold degree of an object based on our feelings;

2. Celsius temperature:

(1) Temperature The commonly used unit is degrees Celsius, represented by the symbol "C";

(2) Celsius temperature regulation: The temperature of the ice-water mixture under one atmospheric pressure is 0℃; the temperature of boiling water under one standard atmospheric pressure is The temperature is specified as 100°C; then the range between 0°C and 100°C is divided into 100 equal parts, with each equal part representing 1°C.

(3) How to read Celsius temperature: For example, "5℃" is read as "5 degrees Celsius"; "-20℃" is read as "minus 20 degrees Celsius" or "minus 20 degrees Celsius"

2. Thermometer

1. Commonly used thermometers are made using the principle of thermal expansion and contraction of liquids;

The composition of a thermometer: glass bubble, uniform glass tube, The glass bubble is filled with an appropriate amount of liquid (such as alcohol, kerosene or mercury) and scale;

Use of thermometer:

Before use: observe the range and graduation value of the thermometer (each (the small scale represents the temperature), and estimate the temperature of the liquid, which cannot exceed the range of the thermometer (otherwise the thermometer will be damaged)

When measuring, the glass bulb of the thermometer must be in full contact with the liquid being measured, and not tightly. Close to the wall and bottom of the container;

When reading, the glass bubble cannot leave the liquid being measured, the reading must be taken after the thermometer's indication is stable, and the line of sight must be level with the upper surface of the night column in the thermometer.

3. Thermometer:

Purpose: specially used to measure human body temperature;

Measuring range: 35℃～42℃; graduation value is 0.1℃ ;

The thermometer can leave the human body when reading;

The special composition of the thermometer: there is an extremely thin, curved tube (constriction) between the glass bubble and the straight glass tube;

Physical changes: changes in the three states of matter: solid, liquid, and gas; solid, liquid, and gaseous states can transform into each other under certain conditions. The state in which matter exists is related to the temperature of the object.

4. Melting and solidification: The change of a substance from solid to liquid is called melting; the change from liquid to solid is called solidification.

Substances must absorb heat when melting and release heat when solidifying;

Melting and solidification are reversible processes of two physical state changes;

Solids can be divided into Crystal and amorphous;

Crystal: a substance that has a fixed temperature (melting point) when melted; amorphous: a substance that does not have a fixed temperature when melted;

The fundamental difference between crystal and amorphous Yes: crystals have a melting point (the temperature remains unchanged when melting and continue to absorb heat), while amorphous crystals have no melting point (the temperature increases when melting and continue to absorb heat); (melting point: the temperature when the crystal melts);

Crystal Conditions for melting:

The temperature reaches the melting point; (2) Continue to absorb heat;

Conditions for crystal solidification: (1) The temperature reaches the freezing point; (2) Continue to release heat;

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The melting point and freezing point of the same crystal are the same;

The melting and solidification curves of the crystal:

(1) The object in segment AB is a solid, and the endothermic temperature increases;

(2) Point B is solid, the temperature of the object reaches the melting point (50°C) and begins to melt;

(3) BC object shares and liquid are stored, absorbing heat and temperature unchanged;

(4) Point C is in liquid state, the temperature is still 50°C, and the object has just melted;

(5) CD is in liquid state, the object absorbs heat and the temperature rises ;

(6) DE is liquid, the object releases heat and the temperature decreases;

(7) Point E is liquid, the temperature of the object reaches the freezing point (50℃) and begins to solidify;

(8) Section EF is where solid and liquid are stored, exothermic, and the temperature remains unchanged;

(9) Point F is solid, solidification is completed, and the temperature is 50°C;

(10) The FG segment is solid, and the exothermic temperature of the object decreases;

Note: 1. The time taken for melting and solidification of a substance is not necessarily the same, which is related to specific conditions;

2. Heat can only be transferred from an object with a high temperature to an object with a low temperature. The condition for heat transfer to occur is: there is a temperature difference between the objects;

5. Vaporization and liquefaction

1. The change of a substance from a liquid state to a gaseous state is called vaporization; the change of a substance from a gaseous state to a liquid state is called liquefaction;

2. Vaporization and liquefaction are mutually reversible processes. Vaporization requires heat absorption and liquefaction requires Release heat;

3. Vaporization can be divided into boiling and evaporation;

(1) Evaporation: Slow vaporization that can occur at any temperature and only occurs on the surface of a liquid Phenomenon;

Note: The speed of evaporation is related to (A) the temperature of the liquid: the higher the temperature, the faster the evaporation (water sprinkled in the room in summer dries faster than in winter; clothes dry faster when dried in the sun); (B) It is related to the size of the surface area of ??the liquid. The larger the surface area, the faster the evaporation (when cooling clothes, you should open the clothes to cool them, and in order to dry the water in the ground quickly, you should sweep away the water); (C) It is related to the air on the surface of the liquid It is related to the speed of flow. The faster the air flows, the faster it evaporates (cool clothes should be kept in a ventilated place, and fans should be turned on to cool down in summer);

Boiling: At a certain temperature (boiling point), the liquid surface and interior Violent vaporization phenomenon that occurs at the same time;

Note: (A) Boiling point: The temperature when a liquid boils is called the boiling point; (B) The boiling points of different liquids are generally different; (C) The boiling point of a liquid is related to pressure. The greater the pressure, the higher the boiling point (pressure cooker cooking) (D) Conditions for liquid boiling: when the temperature reaches the boiling point, it continues to absorb heat;

The difference and connection between boiling and evaporation:

(A) They are both vaporization phenomena and both absorb heat; (B) Boiling only occurs at the boiling point; evaporation can occur at any temperature; (C) Boiling occurs inside and outside the liquid at the same time; evaporation only occurs on the surface of the liquid Carry out; (D) Boiling is more violent than evaporation;

(4) Evaporation can cause cooling: Sprinkle water in the room to cool down in summer; people sweat to cool down; when you have a fever, apply alcohol on the skin to cool down;

(5) Different objects evaporate at different speeds: for example, alcohol evaporates faster than water;

4. Methods of liquefaction: (1) Lower the temperature; (2) Compress the volume (increase the pressure, increase the Boiling point) such as: storage and transportation of hydrogen; liquefied gas;

6. Sublimation and condensation<

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1. The direct change of a substance from a solid state to a gaseous state is called sublimation; the direct change of a substance from a gaseous state to a solid state is called sublimation. Sublimation absorbs heat, and condensation releases heat;

2. Sublimation phenomenon: Mothballs become smaller; frozen clothes dry; physical changes of dry ice in artificial rainfall;

3. Sublimation phenomenon: the formation of snow; ice flowers on window glass in northern winter (on the inner surface of the glass )

7. The formation of clouds, frost, dew, fog, rain, snow, hail and "white gas"

1. When the temperature is higher than 0℃, water vapor liquefies into Small water droplets become dew; they attach to dust and form fog;

2. When the temperature is lower than 0°C, water vapor condenses into frost;

3. Water vapor rises to high altitudes, When it meets cold air, it liquefies into small water droplets, forming clouds, and large water droplets are rain; there are also a large number of small ice crystals and snow (formed by water vapor condensation) in the clouds, and the small ice crystals can melt into rain when they fall, and the small water droplets are then mixed with 0 When the cold air flows at ℃, it solidifies into hail;

4. "White gas" is formed by the liquefaction of water vapor and cold liquid

Chapter 5 Current and Circuits

1. Electric charge

1. When an object has the property of attracting light and small objects, we say that the object is charged, or charged;

2. Using friction The method of charging an object is called triboelectricity;

2. Two kinds of charges:

1. The charge of a glass rod rubbed with silk is called positive charge;

2. The charge on a rubber rod rubbed with fur is called negative charge;

3. Basic properties: Same charges repel each other, and different charges attract each other;

3. Electroscope

1. Purpose: used to test whether an object is charged;

2. Principle: use different charges to repel each other;

4. Charge amount (charge )

1. The amount of charge is called charge, or charge for short;

2. The unit of charge: Coulomb (C), referred to as Coulomb;

5. Yuan Charge:

1. An atom is composed of a positively charged nucleus in the center and negatively charged electrons outside the nucleus;

2. The smallest charge is called an element charge (one electron Charge) is represented by e; e=1.60×10-19;

4. Under normal circumstances, the positive charge carried by the nucleus is equal in quantity to the total negative charge carried by the electrons outside the nucleus equal, the entire atom is neutral;

6. Frictional electrification

1. Reason: The atomic nuclei of different objects have different abilities to bind electrons;

2. The essence of triboelectricity: triboelectricity is not the creation of electricity, but the transfer of electrons from one object to another, losing the positive charge of the electrons. Obtain the negative charge of electrons;

7. Conductors and insulators

1. Objects that are good at conducting electricity are called conductors; such as: metal, human body, earth, acid and alkali salt solutions;

2. Objects that are not good at conducting electricity are called insulators, such as rubber, glass, plastic, etc.;

3. Metal conductors conduct electricity by free electrons, and acid-base and salt solutions conduct electricity by positive and negative ions;

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4. Conductors and insulators can convert into each other under certain conditions;

8. Current

1. The directional movement of charges forms current;

2. A device that can provide power is called a power supply.

The carbon rod of the dry battery is the positive electrode and the zinc cylinder is the negative electrode;

3. Regulation: the direction of directional movement of true charge is the direction of current (the direction of directional movement of negative charge is opposite to the direction of current)

4. Outside the power supply, the direction of current flows from the positive pole to the negative pole of the power supply;

9. Circuit: Use wires to connect electrical appliances, switches, and electrical appliances to form a circuit;

1. Power supply: provides continuous current and converts other forms of energy into electrical energy;

2. Electrical appliances: consumes electrical energy and converts electrical energy into other forms of energy (lights, electric fans, etc.)

3. Wires: transmit electrical energy;

4. Switch: control the on and off of the circuit;

10. Working status of the circuit

1. Path: a circuit that is connected everywhere;

2. Open circuit: a circuit that is disconnected somewhere;

3. Short circuit: directly connect the positive and negative poles of the power supply with wires;

11. Circuit diagram and component symbols:

1. A diagram that uses symbols to represent circuit connections is called a circuit diagram. The commonly used symbols are as follows:

When drawing a circuit diagram, you must Note: The entire circuit diagram is rectangular; the wires must be horizontal and vertical; components cannot be drawn at the corners.

12. Series and parallel connection

A circuit that connects circuit elements one by one is called series connection

Characteristics: There is only one path for current; all electrical appliances interact with each other Influence;

A circuit that connects circuit elements in parallel is called a parallel circuit;

Characteristics: There are multiple paths for current; electrical appliances do not affect each other. When one branch is open, the other A branch can still be a path;

Usually judge series or parallel connection based on the direction of current flow: starting from the positive pole of the power supply, walking around in the direction of the current, and returning to the negative pole, it is a series connection. If there is a branch, it is a series connection. Parallel connection;

13. Circuit connection method

The lines are simple and quick, and no intersections can occur; 2. The order of the components in the physical diagram must be consistent with the circuit diagram ; 3. Generally, start from the positive pole of the power supply, follow the direction of the current, and connect in sequence until returning to the negative pole of the power supply; 4. In parallel circuit connections, first series and then parallel, first branch circuit and then main circuit, find the branch point correctly when connecting. and meeting point. 5. The switch should be turned off before connecting the circuit;

14. The strength of the current

1. Current: a physical quantity indicating the strength of the current, symbol I

2. Unit: Ampere, symbol A, as well as milliamperes (mA), microamps (μA) 1A=1000mA 1mA=1000μA

3. Current intensity (I) equals 1 second. The amount of charge on the cross-section of the conductor; I=Q/t

15. Measurement of current: use an ammeter; symbol A

1. The structure of the ammeter: terminal, range, indication Number and graduation value

2. Use of ammeter

(1) First of all, three things need to be "clearly seen": see clearly the range and whether the pointer is pointing on the scale line, plus or minus Terminal post

(2) The ammeter must be connected in series with the electrical appliance; (equivalent to a wire)

(3) The ammeter must be connected in series with the electrical appliance; (equivalent to a wire)

(4) Select the appropriate range (if you don’t know the range, you should choose a larger range and conduct a test touch.)

Note: Test touch method: first connect one line of the circuit Fix the head and one terminal of the ammeter, and then use the other wire of the circuit to quickly touch the other terminal of the ammeter. If the pointer swings very little (the reading is inaccurate), you need to change to a smaller range. If it exceeds the range (the ammeter will burn out) ), you need to change to a larger range.

3. Reading of the ammeter

(1) Clarify the selected range

(2) Clarify the graduation value (the current value represented by each small grid)

(3) Read the current value according to the number of grids where the meter needle deflects to the right

16. Characteristics of current in series and parallel circuits: The current in a series circuit is equal everywhere; the trunk current in a parallel circuit is equal to the sum of the branch currents;