What and what is light used to propagate?

The principle of light propagation along a straight line can also explain that solar and lunar eclipses can be clearly seen through the graph, the sun cannot reach in area A, so the sun cannot be seen, which is commonly known as a total solar eclipse, and the area A is called the umbra area, and only a part of the light emitted by the sun can reach in the area B and C, so only a part of the sun can be seen, which is what we often call a partial solar eclipse, and the B and C regions are called the penumbra area. On August 1, 2008, we can witness the astronomical phenomenon of solar eclipse in Xinjiang, and interested students remember that it was August 1, 2008.

On thunderstorms, thunder and lightning occur at the same time, but why do we always see lightning first and then hear thunder? This is because light travels faster than sound, so lightning is always seen first.

We know that the speed of sound in the air is 340m s, so what is the speed of light transmission in the air?

As early as 1607, Galileo Galilei carried out the first experiment of measuring the speed of light, his method: let two people stand on two mountains one mile apart, each take a lamp, the first person holds the lamp first, when the second person sees the lamp raised by the first person, immediately raises his lamp, the time interval from the first person holding the lamp to the second person's lamp he sees is the time it takes for light to travel two miles, but because the speed of light travels too fast, the time taken is almost zero, So he didn't measure the speed of light this way. In the more than 300 years since, many scientists have conducted experiments to determine the speed of light, but the results have not been satisfactory.

It was only in 1972 that Evenson of the United States measured the exact value of the speed of light.

Down we say light. Before Einstein, it was thought that light traveled through the ether, but later experiments overturned the ether.

There is a certain law in the propagation of light, and mastering this law can make it serve human beings.

Transparent substances in which light energy travels, such as air, glass, etc., are called the medium in which light is propagated.

Light travels in a straight line in a uniform medium. Depending on the medium, the propagation of light will change.

Fill the glass with water and add a few drops of milk to make the water a slightly cloudy white liquid. If you then shine a flashlight diagonally on the surface of the water, you will find that the light travels in a straight line after entering the water.

However, when passing through the interface of water and air, the direction of light propagation changes. This phenomenon is called refraction of light.

The ray of light that travels into the water is called a refracted line. The angle between the refractive line and the normal is called the refractive angle.

When light is emitted from air into water, the angle of refraction is always less than the angle of incidence.

If it enters air from water, the angle of refraction is greater than the angle of incidence.

1. Brightness: Brightness indicates the intensity of light. It varies with the energy and distance of the light source.

2. Direction: There is only one light source, and the direction is easy to determine. With multiple light sources, such as diffuse light from cloudy weather, the direction is difficult to determine or even completely lost.

3. Color: Light changes a variety of colors with different sources of light and with the different substances it passes through. The color of natural light is different from that of incandescent light or electronic flash, and the color of sunlight itself also varies with atmospheric conditions and the time of day.

Ask questions about the role of light.

Light travels in a straight line (in a homogeneous medium), but when the light meets another medium (homogeneous medium), the direction changes, and it still travels in a straight line. Whereas, in a non-homogeneous medium, light generally travels in a curve. The propagation path of the above light can be determined by Fermat's principle.

When the brightness of the light is darker, the light from the luminaire to the illumination reference object will expand, the farther the distance, the greater the diffusion, from the initial shape to the disappearance, and when the luminous body is zero distance from the illumination reference object, the shape of the light is the real shape size of the luminous body, so the direction of light propagation is related to the brightness of the light and the distance between the light and the illumination reference object.

1.In geometric optics, light travels in a straight line. This is illustrated by the straight pillars of light and the sun's rays. 2.In wave optics, light travels in the form of waves. Light is like water waves on the surface of the water, and different wavelengths of light appear different colors.

Light travels in a straight line in the same homogeneous medium. Aperture imaging, solar and lunar eclipses, and shadow formation all testify to this fact.

Aside from the wave nature of light, the discipline that studies the propagation of light in a medium and the laws of object imaging based on the linear propagation of light is called geometric optics. In geometrical optics, a geometric line with an arrow represents the direction of light propagation, which is called light. Geometrical optics regards an object as a combination of countless points (in approximation, objects can also be used to represent objects), and the beam of light emitted by the points is regarded as a collection of countless geometric rays, and the direction of the light represents the direction of light energy transfer.

There are three laws of light propagation in geometric optics:

1) The law of linear propagation of light is as described above. Geodetic surveys are also based on this.

2) The law of independent propagation of light. When two beams of light meet each other in the process of propagation, they do not interfere with each other, and continue to propagate in their respective ways, and when the two beams of light converge at the same point, the light energy at that point is simply added.

3) The law of reflection and refraction of light.

When light travels through the interface of two different media, part of it is reflected and part of it is refracted.

Reflected rays follow the law of reflection, and refracted rays follow the law of refraction.