1, the appearance of sound

Everything that makes a sound vibrates. When the vibration stops, the sound will also stop.

Sound is produced by the vibration of objects, but not all the sounds produced by vibration can be heard by human ears.

2. Transmission between voices

The transmission of sound needs medium, and vacuum cannot transmit sound.

(1) All gases, liquids and solids can transmit sound. These substances as media are called media. Even if astronauts on the moon talk face to face, they still need to rely on radio. That's because there is no air on the moon, and vacuum can't spread sound.

(2) Sound travels at different speeds in different media. Generally speaking, solid >: liquid > air.

The speed of sound in the air is about 340 meters per second.

Step 3 echo

In the process of sound propagation, the sound that people hear again when they encounter obstacles is called echo.

The distinguishing condition between echo and original sound: the echo reaches people's ears more than 0. 1 second later than the original sound. Therefore, the sound must be reflected by obstacles with a distance exceeding 17m, so that people can hear the echo.

Below 0. 1 sec, the reflected sound can only strengthen the original sound.

Use echo to measure the depth of the sea or to detect how far an object is from an obstacle.

4. Music

The sound made by an object when it vibrates regularly is called music.

Three elements of musical sound: tone, loudness and timbre.

The sound level is called tone, which is determined by the vibration frequency of the speaker. The higher the frequency, the higher the pitch.

The size of sound is called loudness, which is related to the amplitude of speaker vibration and the distance from the sound source to the human ear.

The quality of sound produced by different vocal bodies is called timbre. Used to distinguish different sounds.

5. Noise and its sources

From the physical point of view, noise refers to the sound made by the vocal body when it vibrates irregularly. From the perspective of environmental protection, all sounds that hinder people's normal rest, study and work, as well as those that interfere with people's desire to hear, belong to noise.

6, the division of sound level

People use decibels to divide sound levels. 30 dB -40 dB is an ideal quiet environment. If it exceeds 50dB, it will affect sleep; If it exceeds 70dB, it will interfere with the call and affect the work efficiency. If you live in a noise environment above 90dB for a long time, it will affect your hearing.

7. Ways to reduce noise

It can be weakened at the sound source (noise elimination), during propagation (sound absorption) and at the human ear (sound insulation).

Chapter II Light Phenomenon

1. Light travels in a straight line in the same uniform medium. The linear propagation of light can explain many common phenomena, such as shadow formation, solar eclipse and lunar eclipse.

2. Light is a straight line indicating the direction of light propagation. When drawing light, you must use arrows to indicate the direction of light propagation.

3. The propagation speed of light in different media is not equal. The maximum speed of light in vacuum is 3× 108 m/s, and the speed of light in other media is less than that in vacuum. The speed of light in air is close to vacuum, and it can also be considered as 3×108 m/s.

4. When the light shines on the surface of the object, it will be reflected by the surface of the object. This phenomenon is called light reflection.

5. The straight line perpendicular to the mirror from the incident point o of light is called normal. The angle between the incident light and the normal is called the incident angle.

Represented by symbol I, the angle between the reflected light and the normal is called the reflection angle, and represented by symbol R.

6, the law of light reflection:

A. reflected light, incident light and normal are on the same plane.

B, reflected light and incident light are separated on both sides of the normal.

C. the emission angle is equal to the incident angle.

7. A smooth surface reflects light in the same direction, which is called specular reflection.

8. An uneven surface will reflect light in all directions, which is called diffuse reflection.

9. Whether it is specular reflection or diffuse reflection, the reflection of each ray obeys the law of light reflection.

10, the characteristics of plane mirror imaging: the distance from the image to the mirror is equal; The image is the same size as the object; The connecting line between the image and the corresponding point on the object is perpendicular to the mirror surface (that is, the image and the object are symmetrical about the mirror surface); The image formed by the plane mirror is a virtual image.

1 1. Virtual image: it is not formed by the intersection of actual lights and cannot be accepted by the screen.

12. When light obliquely enters another medium from one medium, the propagation direction generally changes. This phenomenon is called light refraction. Even in the same medium, if the medium is not uniform, light will be refracted. When light is vertically incident on the interface, its propagation direction remains unchanged.

13, and the angle between the refracted light and the normal is called the refraction angle.

14. When light is obliquely incident from air into water or other media, the refracted light is deflected to the normal direction, and the incident angle is greater than the refraction angle; When light enters the air obliquely from water or other media, the refracted light deflects towards the interface, and the refraction angle is greater than the incident angle. (The angle between the light in the air and the normal is always large, that is, "the empty angle is large")

15, the water depth seen by the eyes is deeper than the actual water depth; Chopsticks inserted obliquely into the water appear to bend upward in the water; See the sun set below the horizon; Aim below the fish when you fork it; Mirages and other phenomena are caused by the refraction of light.

16, concave mirror (reflection) can make parallel light converge, which can be used to make solar cookers. According to the principle of reversible light path, the focused light source can reflect parallel light-flashlight.

17, convex mirror (reflection) can make parallel light diverge and increase the field of vision. Example: car rearview mirror, mirror at the corner of the street.

18, in the reflection and refraction of light, the optical path is reversible.

camera lens

1, thick in the middle and thin in the edge is called convex lens; The one with a thin center and thick edges is called a concave lens.

2. Convex lens (refraction) can condense light; Concave lens (refraction) has divergent effect on light.

3. The straight line passing through the centers of two spherical surfaces is called the main optical axis of the lens. There is a special point on the main optical axis, and the propagation direction of light through it remains unchanged. This point is called the optical center of the lens. It can be considered that the optical center is in the center of the lens.

4. The convex lens can make the light parallel to the main optical axis converge at a point on the main optical axis, which is called the focus of the convex lens. The distance from the focal point to the optical center of the convex lens is called the focal length. There is a focal point on each side of the convex lens, and the two focal lengths on both sides are equal, with F as the focal point and F as the focal length.

5. The parallel rays become divergent after passing through the concave lens, and the reverse extension lines of these divergent rays intersect at a point on the main optical axis, which is called the virtual focus of the concave lens.

6. Present situation and application of convex lens imaging

This is the case with the distance U from the object to the convex lens, and the distance V from the object to the convex lens is the application or demarcation point.

Invert or stand upright to enlarge or reduce the real image or virtual image.

U> real image is reduced by 2f inversion >: v > F camera

U = 2f inverts the boundary point of the image size of other real images V = 2f.

2f>U>f Inverted Magnifying Real Image V & gt2f Projector and Slide Show Machine

U = f does not image. When the light source is placed in focus, the boundary point between the virtual image and the real image of parallel light can be obtained.

U< vertical magnification virtual image V> magnifying glass

7. Real image refers to the image formed by the intersection of the light emitted by the object and the actual light after passing through the optical fixture. It is a pattern similar to the original by gathering real light spots. Real images can be presented on the screen and exposed with negatives. Aperture imaging, cinema screen images, camera images and projector images are all real images. The real images formed by the convex lens are all inverted, and the images and objects are on both sides of the convex lens respectively.

8. Virtual image refers to the light emitted by an object, which diverges rather than converges after passing through an optical fixture. It is an image formed by the intersection of opposite extension lines of these divergent rays. Virtual images cannot be presented on the screen, nor can the negative be sensitized. They can only observe with their eyes. The images formed by the plane mirror, convex mirror, concave mirror and convex lens of an object in the focal length are all virtual images. When the convex lens becomes a virtual image, the object must be placed at a place less than the focal length. At this time, the convex lens acts as a magnifying glass, and both the image and the object are on the same side of the convex lens.

9. When the object distance of the convex lens is greater than the image distance, it becomes an inverted reduced real image; When the object distance is equal to the image distance, it becomes a real image with inverted size; When the object distance is less than the image distance and greater than the focal length, it becomes an inverted magnified real image.

10, the eyeball is like a camera. The interaction between cornea and lens is equivalent to a convex lens, which focuses the light emitted by the object on the retina to form the image of the object.

1 1, eyes can see different objects clearly, and the lens thickness can be changed through the ciliary body, thus changing the lens focal length of this advanced camera.

12. The reason of myopia is that the lens is too thick and has too strong refraction ability to light, which makes distant objects image in front of the retina and can be corrected by the divergence of concave lens.

13. The reason for hyperopia is that the lens is too thin and its refraction ability to light is too weak, so that the near object can be corrected by the convergence of the convex lens after imaging in the retina.

14. There are a set of lenses at each end of the microscope barrel. Those close to the eyes are called eyepieces, and those close to the observed objects are called objective lenses. The light from the observed tiny object passes through the objective lens and becomes an inverted magnified real image. The function of the eyepiece is to enlarge the image again and act as a magnifying glass.

15, the objective lens and eyepiece of the telescope are composed of convex lenses respectively. The function of the objective lens is to make the distant object become an inverted and reduced real image near the focus, which is equivalent to bringing the distant object closer to the eyes and increasing the viewing angle. The function of the eyepiece is to enlarge the image and act as a magnifying glass, which is equivalent to increasing the viewing angle again.

16, the visual angle of an object to the eyes is not only related to the size, but also related to the distance. The bigger the angle of view, the clearer you can see.