Explanatory text about light

Light is an electromagnetic wave (visible spectrum) visible to human eyes. In the scientific definition, light sometimes refers to all the electromagnetic spectrum. Light is made up of a kind of elementary particles called photons. With particles and fluctuations, or wave-particle duality [1]. Light can propagate in transparent substances such as vacuum, air and water. aurora

Speed of light: The speed of light in vacuum is 300,000 kilometers per second (to be exact, C = 299,792,458 m/s), and it takes only eight minutes for light to travel from the sun to the earth. Visible light visible to the naked eye is only a part of the whole electromagnetic spectrum. The visible spectrum of electromagnetic wave is about 390 ~ 390 ~ 760 nm (0.00000001+0), and light can be divided into artificial light and natural light. Objects that emit light by themselves are called light sources, which are divided into cold light sources and hot light sources. The picture shows an artificial light source. Fireworks in the night sky

Experiments show that light is electromagnetic radiation, and the wavelength range of this part of electromagnetic wave is about 0.77 micron of red light to 0.39 micron of purple light. Electromagnetic waves with a wavelength of more than 0.77 micron to about 1000 micron are called "infrared rays". Below 0.39 micron to about 0.04 micron is called "ultraviolet". Infrared and ultraviolet rays can't cause vision, but the existence of this luminous object can be measured and detected by optical instruments or photography. Therefore, the concept of light in optics can also be extended to infrared and ultraviolet fields. Even X-rays are considered as light, and the spectrum of visible light is only a part of the electromagnetic spectrum. Light has wave-particle duality, that is, it can be regarded as a kind of electromagnetic wave with high frequency, and it can also be regarded as a particle, called photon for short. The speed of light replaced the platinum watch kept in the International Bureau of Metrology in Paris as the standard for defining "meter", and it was agreed that the speed of light was strictly equal to 299,792,458 m/s, which was consistent with the definition of meter and second at that time. Later, with the continuous improvement of experimental accuracy, the numerical value of the speed of light changed. The meter is defined as the distance traveled by light in 1/299792458 seconds, and the speed of light is represented by "c". Light is one of the sources of life on earth. Light is the foundation of human life. Light is a tool for human beings to know the outside world. Light is an ideal carrier or media of information. According to statistics, at least 90% of all information received by human senses from the outside world is transmitted through the eyes ... When a beam of light is projected on an object, it will be reflected, refracted, interfered and diffracted. Light travels in a straight line in a uniform medium. Light waves, including infrared rays, have shorter wavelengths and higher frequencies than microwaves. Therefore, it is a natural and inevitable trend to develop from microwave communication in electrical communication to optical communication. Ordinary light: Generally speaking, light is composed of many photons. Under fluorescence (ordinary sunlight, light, candlelight, etc.). ), there is no connection between photons, that is, different wavelengths, different phases, different polarization directions and different propagation directions, just like an unorganized and undisciplined photon army, all photons are stragglers and cannot act in unison. When light is reflected, the reflection angle is equal to the incident angle. On the same plane, on both sides of the normal, the light path can be reversed. Light incident obliquely from one medium to another will produce refraction. If the density of the injected medium is greater than the original starlight

When the light is in a medium density, the refraction angle is smaller than the incident angle. On the other hand, if it is greater than, the refraction angle is greater than the incident angle. However, if the incident angle is zero and the refraction angle is zero, no refraction will occur. However, light refraction still occurs in the same inhomogeneous medium. Theoretically, it can be injected from one direction without refraction. However, due to the unclear boundary, it is generally divided into several levels and is not flat, so refraction will occur anyway. For example, looking at the calm lake bottom from the shore belongs to the first refraction, but seeing a mirage belongs to the second refraction. The function of convex lens and concave lens is due to the first refraction. Laser-In the new world of optics, all photons are interrelated, that is, they have the same frequency (or wavelength), phase, polarization direction and propagation direction. Laser is like a disciplined photon army, acting in unison, so it has strong combat effectiveness. This is the main reason why laser can do many things, but sunlight, light and candlelight can't. There are three types of light sources. The first is the light produced by thermal effect. Sunlight is a good example. Besides, candles and other items are the same. This light will change color with the change of temperature. The second is atomic luminescence. The fluorescent substance coated on the inner wall of fluorescent tube is excited by electromagnetic wave energy to produce light, and the principle of neon lamp is the same. Atomic luminescence has its own basic color. The third is the synchrotron, which emits powerful light. This is the light from the atomic furnace, but we rarely have the opportunity to come into contact with this light in our daily life. Dispersion of light The phenomenon that polychromatic light is decomposed into monochromatic light is called optical dispersion. Newton first observed the dispersion of light with a prism in 1666, and decomposed white light into colored bands (spectra). Dispersion phenomenon shows that the speed (or refractive index n=c/v) of light in the medium varies with the frequency of light. The dispersion of light can be achieved by using prisms, diffraction gratings, interferometers, etc. White light is composed of red. Colors such as red, orange, yellow and green are called monochromatic light. Dispersion: The phenomenon that polychromatic light is decomposed into monochromatic light to form spectrum is called optical dispersion. Using prism or grating as "dispersion system" can realize dispersion. After entering the prism, polychromatic light has different refractive indexes for light with various frequencies, and the propagation direction of polychromatic light is deflected to varying degrees, so when leaving the prism, they are dispersed separately to form a spectrum. The phenomenon that the dispersion refractive index of light varies with the frequency of light wave or the wavelength in vacuum. When polychromatic light refracts at the interface of the medium, the medium has different refractive indexes for light with different wavelengths, and the light of each color is separated from each other due to different refraction angles. 1672, Newton used a prism to decompose sunlight into colored bands, which was the first dispersion experiment made by people. The relationship between refractive index n or dispersion ratio DN/D λ and wavelength λ is usually used to describe the dispersion law. The dispersion of any medium can be divided into normal dispersion and abnormal dispersion. The phenomenon that polychromatic light is decomposed into monochromatic light to form a spectrum. Let a beam of white light shine on the glass prism, and after the light is refracted by the prism, a colored light band will be formed on the white screen on the other side. The color arrangement is red near the top corner of the prism, purple at the end near the bottom, and orange, yellow, green and indigo in the middle. This band of light is called spectrum. Each color of light in the spectrum cannot be decomposed into other colors of light. It is called monochromatic light. Light mixed with monochromatic light is called polychromatic light. The light emitted by sunlight, incandescent lamps and fluorescent lamps in nature is polychromatic light. When light shines on an object, part of the light is reflected by the object and part of the light is absorbed by the object. If the object is transparent, there is still a part passing through it. Different objects reflect, absorb and transmit different colors, so they show different colors. sunlight

For example, when yellow light shines on a blue object, it appears black, because the blue object can only reflect blue light, but not yellow light, so if it absorbs yellow light, it can only see black. But if it is white, it reflects all colors. The essence of light: the electrons outside the nucleus gain energy and jump to a higher orbit. This orbit is unstable, but it will jump back and release a photon, which is in the form of light. The energy released is different, and the wavelengths of different photons are different. What is light? It is a problem worth studying, and it is also necessary to study. Today, the school of physics has reached a bottleneck, that is, the conflict between relativity and quantum theory. Whether the essence of light is elementary particles or waves like sound (if waves propagate in any medium) is instructive for future research. At present, the reasonable view is that light is both a particle and a wave, which has the duality of wave and particle, just like the relationship between water droplets and water waves.