Acoustics Optical problems, what is the difference between optical phonon and acoustic phonon

U is used for object distance and F for focal length.

When u f, it is not a reality.

f u 2f, into an inverted enlarged real image.

U=2F, a large inverted solid image of the equal.

U 2F, into a handstand shrunken real image.

The larger the object distance, the smaller the image distance.

The above is the basic knowledge, which is available in physics books.

d to make the image larger, the lens should be closer, that is, reduce u to make the image larger, and at the same time the image becomes larger, then the image is farther away, the image distance becomes larger, then the distance between the slide projector and the screen should be larger, and the slide projector should be pulled back.

d No imaging at 1x focal length. (The closer the object, the farther away the image.) When the object is infinitely present on the premise of imaging, then the image is infinitely far away, and when the image is infinitely close, the object is infinitely far away. )

When moving in 1 2x focal length, the object moves from 1x to 2x, while the image moves from infinity to 2x focal length, and both the object and the image move to 2x focal length. The distance between the two is reduced from infinity to 4x focal length, so it is said to be reduced.

When moving beyond the 2x focal length, the object moves towards infinity, as if moving from 2x to 1x. From a distance of 4x focal length to infinity, it is said to have increased.

Therefore, it decreases first and then increases.

The propagation of sound requires a medium, and on the earth, because there is air as a medium, the air vibrates and transmits the sound, causing the ball to be bounced away. But on the moon there is no air. I can't transmit the vibration to Xiaoqiu. As a result, the ball will stand still.

It should be one less item, that is, an object that can produce the effect of imaging small holes.

Given the time t, the speed of light c is known, then the distance between the sun and the earth l=ct is also known. Then as long as the radius r of the image and the distance l between the image and the object are measured, then the radius r of the sun can be obtained according to the principle of similar triangles.

r:r=l:l

r=lr/l

If you increase the distance and decrease the distance between objects, the image will be larger.

1. Exercise is different.

In optical mode, the atoms in the unit cell move relatively.

In acoustic mode, the crystal is sensitive to overall combustion.

2. The frequency is different.

The frequency of the optical mode is close to that of electromagnetic waves, and it is easy to couple with electromagnetic fields.

The acoustic mode can be seen as a continuum of elastic waves at low frequencies.

3. The way of existence is different.

The acoustic phonon is imperceptible, and the root cause of this is the spontaneous breakdown of translational symmetry.

Optical phonons exist only in polyatomic cells and arise from the absolute vibration of different atoms in the cell.

1 What is the process of bone conduction?

Normal sound is conducted through the human ear, eardrum, and nerves, while bone conduction is not conducted through the ear, but through the human body itself, not through the eardrum. In the simplest way, someone knocks you on the head, and you yourself listen to it very loudly, while the person standing next to you barely hears anything with their ears, because the vibrations act directly through your skull to the auditory nerve in your head.

2. Put the ruler on the table, why the shorter the protrusion, the greater the frequency. 、

The shorter the extension, the shorter the ruler will vibrate back and forth once, and the higher the frequency (this is easy to understand).

3 Please explain from the onlookers, how does the medium transmit sound? Why is the speed different?

The medium transmits sound through the vibration between the molecules of the substance itself, such as water, which is the most intuitive to look at, and another example is to knock on the handrail of the staircase, and the person in the distance will feel the vibration (numbness) of his hand when he knocks on the handrail of the staircase

Because the arrangement and density of the molecules of different substances and the forces between the molecules are different, the speed of sound transmission is different in different media.

4. How sound transmits energy.

As mentioned above, sound is transmitted through the vibration between the molecules of the medium, and the sound itself carries energy, and the process of molecular vibration to transmit sound is itself an energy transmission process.

I hope I've made it clear enough.

4. How sound transmits energy.

Law of gravitation: f=gmm r 2; The law of universal repulsion: f=hww r 2

ff = ghmmww r 4 (ear power product).

Then add the ear power formula).

Two sounds, one for the air and one for the rails. The distance is the same:

l/340=l/500+4

Get: l=4250m.

A: The track is 4250 meters long.

However, it seems that the sound in the steel is not only 500 meters and seconds, but also 5,000 meters and seconds.

If it is 5000 meters per second, l = meters.

The topic is very easy to do.

Distance = Velocity Difference * Time.

Distance and other speed difference multiply time.

But there is a common sense problem with this topic, who came out of it, you go to him.

The speed of sound in steel is extremely fast, it has to be 5000 meters per second, not 500, and the speed of sound in water is still 1500 meters per second, even if you change 500 to 5000 in the above question, because sound can run 1360 meters in 4 seconds in the air, and the sound of hitting the railroad track with a hammer at 1360 meters outside cannot be heard through the air, unless it is downwind.

Logically, it can only be the first container without iron blocks, because the last two should be measured at the same time.

It is understood that the energy of sound waves is very small and cannot penetrate such a thick piece of iron at all, so if the other party has a container of iron, the sound wave will produce diffraction and continue to move forward around the iron, so they travel a large distance and take a long time.