Common sense about light

The essence of light is electromagnetic waves that can cause vision, and it is also particles (photons).

Light can propagate in transparent substances such as vacuum, air and water. Light speed: The speed of light in vacuum is | 300,000 kilometers per second.

Visible light visible to the naked eye is only a part of the whole electromagnetic spectrum. The visible spectrum of electromagnetic wave is about 390~760nm( 10-9m), and light can be divided into artificial light and natural light.

Light sources are divided into cold light sources and hot light sources; Light source: An object that can emit light by itself is called a light source. Cold light source: it means to emit light without heating (or to generate heat at a very low temperature).

Such as fireflies; Thermal light source: refers to light emitting and heating (must be high temperature heat). Such as the sun; 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 that of the original light, the incident angle is less than the refraction angle.

On the other hand, if it is less than, the incident angle is greater than the refraction 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, so we need to make corresponding corrections when shooting colors.

The third is that synchrotron emits light and carries powerful energy. This is the kind of light emitted by an atomic furnace, which we hardly touch in our daily life. It is enough to remember the first two. 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/dλ 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 the light passes through the prism.

2. Overview of light phenomenon knowledge

Chapter II Light Phenomenon

1. Propagation of light

What can shine is called a light source, and the moon is not the sun. The propagation of light is conditional, and the uniform medium is straight.

The speed is different in different objects, and the vacuum is 300 thousand kilometers per second. C = 3 *105km/s = 3 *108km/s.

The speed of light is faster than the speed of sound, and vacuum light will not disappear.

2. Light reflection

The normal line passes through the incident point, and the dotted line is perpendicular to the reflecting surface. Reflection is incident on both sides, and the angle of anti-angle is always equal.

The normal included angle is the incident angle, and the dihedral angle increases with the increase of incident angle. All objects are reflective, and specular reflection is diffuse on the opposite side.

3. Plane mirror imaging

Plane mirror, virtual image, equal size, strong symmetry. The distance from the object image to the mirror is equal, and they connect the vertical mirror.

Drawing reflection is extended, and the intersection of dotted lines is the image point. All the image points form an image, and the virtual image should be represented by the virtual image.

4. Refraction of light

Light goes from one thing to another, and at the same time it reflects and refracts. The diagonal line will be refracted when it enters the water, and the broken line will be close to the normal.

The normal is perpendicular to the interface, and the dotted line is divided into two sides. The light in the water slants into the air, and the dotted line is far from the normal.

Seen from underwater, the trees are taller, and seen from the shore, the fish are shallower. What the human eye feels is linear light, but what it sees is virtual image.

5. Scattering of light

Red, orange, yellow, green, indigo, purple and white light have seven colors of dispersion. The three primary colors are red, green and blue, and the three primary colors are red, blue and yellow.

Red objects reflect red light and all other colors are absorbed. No reflected light entered my eyes, and I saw a piece of black.

All colors of light are reflected and objects appear white. All colors are completely absorbed, and black is an object.

All colors of light can pass through, and this object is colorless and transparent.

6. Invisible light

Infrared light other than red light, the higher the temperature, the stronger the radiation. Use infrared night vision equipment and often use remote control.

Ultraviolet rays other than violet light help the body synthesize D (vitamin). Ultraviolet rays kill microorganisms and make fluorescent substances glow.

3. Physics

1. Edit the original meaning of electromagnetic spectrum visible to human eyes This paragraph introduces that light is electromagnetic wave visible to human eyes, also known as visible spectrum.

In the scientific definition, light refers to all the electromagnetic spectrum. Light is composed of photons as basic particles, which has particle property and fluctuation, and is called wave-particle duality.

Light can propagate in transparent substances such as vacuum, air and water. The range of visible light is not clearly limited, and the wavelength of light acceptable to ordinary people's eyes is between 380-760nm.

The light people see comes from the sun or with the help of light-emitting devices, including incandescent lamps, fluorescent tubes, lasers, fireflies and so on. Because light is an indispensable material for human survival, there are many idioms about light and songs of the same name.

Editing the Mystery of Light1The research results of james clerk maxwell, one of the great physics giants in the 9th century, came out, and physicists had a clear understanding of the laws of optics. In a sense, Maxwell is the antithesis of michael faraday.

Faraday has amazing intuition in experiments but has no formal training at all, while Maxwell, who is contemporary with Faraday, is a master of advanced mathematics. He is good at mathematics and physics at Cambridge University, where isaac newton finished his work two centuries ago.

Newton invented calculus. Calculus is expressed in the language of "differential equation", which describes how things smoothly undergo subtle changes in time and space.

The motions of waves, liquids, gases and shells can all be described by the language of differential equations. Maxwell started his work with a clear goal-to express Faraday's revolutionary research results and his position with accurate differential equations.

Maxwell first discovered that Faraday electric field can be transformed into magnetic field and vice versa. He adopted Faraday's description of the force field and rewrote it in the precise language of differential equations, and got one of the most important equations in modern science.

They are a set of eight seemingly very difficult equations. Every physicist and engineer in the world must try to digest these equations when he learns to master electromagnetism at the graduate level.

Later, Maxwell asked himself a decisive question: If magnetic fields can be transformed into electric fields, and vice versa, what will happen if they are transformed into each other forever? Maxwell found that these electromagnetic fields can produce a wave, which is very similar to ocean waves. To his surprise, he calculated the speed of these waves and found that it was the speed of light! After 1864 discovered this fact, he prophetically wrote: "This speed is so close to the speed of light that it seems that we have every reason to believe that light itself is an electromagnetic interference."

This may be one of the greatest discoveries in human history. For the first time in history, the mystery of light was finally revealed.

Maxwell suddenly realized that the brilliance of sunrise, the red flame of sunset, the gorgeous colors of rainbow and the twinkling stars in the sky can all be described by the waves he hastily wrote on a page. Today, we realize that the whole electromagnetic spectrum-from TV antenna, infrared ray, visible light, ultraviolet ray, X ray, microwave and gamma ray-is just Maxwell wave, that is, Faraday force field of vibration.

According to Einstein's theory of relativity, light will be distorted when it passes through a strong gravitational field. Light has wave-particle duality.

20 12, New Sea Space-time is discussed in light space-time. In the world of light, it is impossible for human beings to observe superluminal matter, and light is the limit speed thing that human beings can know. It is precisely because of this that light created the human world. The scientific light for editing this paragraph of light is the electromagnetic wave (visible spectrum) that can be seen by human eyes.

In scientific definition, light sometimes refers to all the electromagnetic spectrum. Light is made up of a kind of elementary particles called photons.

It is characterized by particles and fluctuations, or wave-particle duality. Light can propagate in transparent substances such as vacuum, air and water.

The speed of aurora (9 photos): the speed of light in vacuum is the fastest in the universe, and it is represented by C in physics. Light can travel 299792458m in vacuum 1s, that is, the speed of light in vacuum is c = 2.9992458 *108 m/s.

The speed in other media is lower than that in vacuum. The speed of light in air is about 2.99792000 *10.8m/s.

In our calculation, the speed of light in vacuum or air is taken as c = 3 *10.8m/s (the fastest and ultimate speed). The speed of light in water is much smaller than that in vacuum, about 3/4 of that in vacuum. The speed of light in glass is smaller than that in vacuum, about 2/3 of that in vacuum. If a flying man circles the earth at the speed of light, 1s can circle the earth 7.5 times. It takes 8 minutes for sunlight to reach the earth. If a 1000km/h racing car keeps running, it will take 17 years to run the distance 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 ~ 760 nm (1nm =10-9m = 0.00000001m), and light is divided into artificial light (such as laser) and natural light (such as sunlight).

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 have been proved by experiments that light is electromagnetic radiation, and the wavelength range of this 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. Human eyes have different sensitivities to different wavelengths of visible light.

Experiments show that normal human eyes are most sensitive to yellow-green light with a wavelength of 555nm, that is, the radiation with this wavelength can cause the maximum vision of human eyes, and the more it deviates from the radiation with a wavelength of 555 nm, the lower its visibility. 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 original platinum rice kept in the International Bureau of Metrology in Paris.

4. Some knowledge about light diffraction. I am not familiar with this knowledge.

About the diffraction of light: 1, Phenomenon: When the size of an obstacle [or hole] can be compared with the wavelength of light, light can bypass the obstacle and reach the place where it is a shadow.

2. Diffraction is the characteristic of wave, so the supporters of wave theory think that the essence of light is wave. 3. Essence: From the wave point of view, when light meets obstacles [or holes], the wavefront is divided into several point wave sources. The light emitted by these light sources is superimposed in the process of propagation, and a certain area is strengthened and a certain area is weakened, so it becomes a stripe of alternating light and dark [where it is strengthened is bright]; From the point of view of particles, photons bypass obstacles and have different chances of reaching each point. Bright stripes are the places where photons have a high chance of reaching.

4. Modern science believes that light has wave-particle duality, and a large number of low-energy photons are easy to show the fluctuation of light. Small energy means large wavelength, and obstacles are easy to match to form diffraction; From the point of view of particles, the energy is very small, and the performance of a single photon is difficult to detect. Only a large number of photons can be easily detected, so there is diffraction due to the probability of particle appearance. 5. Grating diffraction is a kind of diffraction in which several stripes are carved on the glass slide at equal distance and light passes through them. This experiment is easy to do, very obvious.

6. It is easy to do diffraction experiments with laser [single frequency]. Current laser sources are easy to find.

Children's toy laser flashlight.

5. Knowledge about lamps and lanterns

What is an incandescent lamp?

Incandescent lamp is the original light source. After some improvements, this lamp still uses the basic technology of 100 years ago.

Tungsten wire is placed in a glass bulb and current passes through it. The resistance of the filament causes it to heat up and emit incandescent light or light. Nowadays, incandescent lamps all use coil filament to improve efficiency and reduce heat loss. However, the early bulbs used vacuum technology to prevent the filament from burning due to the combination with oxygen, but now they use a variety of inert gases to achieve the same goal.

Characteristics of incandescent lamp

Incandescent lamp is the most commonly used electric light source in the home. Incandescent lamps with low color temperature and high color rendering index emit warm light. In addition, incandescent lamps are cheap and can be controlled by cheap dimmers of various sizes, specifications and wattage. Unfortunately, incandescent lamps have low luminous efficiency. Because light is generated to heat solid materials until they emit light, most of the energy consumed by incandescent lamps is in the form of heat energy, which leads to low luminous flux per watt.

6. About astronomical knowledge

▲ The universe is infinite [just like the surface of the earth, it has a certain size (that is, it is limited), but it has no edges. The universe is also limited, but the gravity of the universe itself is so great that the space in the universe bends back to itself (just like a circle, only four-dimensional). ]

▲ There is no matter (including time, space and light) outside the universe, so there is no "thing".

But some scientists believe that there are other "universes" besides our universe.

▲ When a star whose mass is more than 0/00 times that of the sun/kloc runs out of fuel, its huge gravity will compress its volume to "0". The density of this point will be infinite, the gravity will be great, and even the space can be bent to attract light, electricity, signals and so on (this point is called a black hole).

▲ First of all, it shows that the speed of motion of matter can only be less than or equal to the speed of light, which can be obtained from the time expansion formula (relativity).

Because the speed of matter can only be less than or equal to the speed of light, when its speed is close to the speed of light, if time slows down, it can only stay below the speed of light forever. When speed = the speed of light, time stops.

Understanding: When the speed of a moving object approaches the speed of light, time slows down, so if the time of a stationary object (relative to a moving object) passes 50 years, then the time of a moving object (relative to a stationary object) may only pass 1 second, so a stationary person is 50 years older than a moving person. The time to move an object is extremely slow, as slow as 1 sec, which is equivalent to 50 years. )

7. Knowledge network diagram of emergent light phenomenon

Chapter II Light Phenomenon

Light source: an object that can emit light

Straight-line propagation of light: In the same homogeneous medium, light propagates along a straight line.

Light speed: c = 3.0 *108m/s.

Dispersion: the phenomenon that polychromatic light is decomposed into monochromatic light.

The three primary colors of light: red, green and blue.

The three primary colors of pigment: red, yellow and blue.

The surface of any object will reflect light.

Law of light reflection: reflected light is in the same plane as incident light and normal line; Reflected light and incident light are separated on both sides of the normal; The reflection angle is equal to the incident angle.

The light path is reversible.

Reflection types: specular reflection and diffuse reflection.

Imaging characteristics of plane mirror: the object image is symmetrical about the mirror surface.

That is, the distance between the object and the image is equal to the plane mirror, and the connecting line between the object and the image is perpendicular to the mirror, like an upright and equal virtual image.

The essence of image: equal size, upright position and virtual image.

Virtual image: it is formed by the convergence of the reverse extension lines of reflected light.

Application: changing optical path and imaging.

When light is obliquely incident from one medium to another, the propagation direction generally changes, which is called light refraction.

When light is obliquely incident from the air into water or other media, the refracted light is on the same plane as the incident light and the normal; Refracted light and incident light are separated on both sides of the normal; The refraction angle is smaller than the incident angle; When the incident angle increases, the refraction angle also increases; When the light is perpendicular to the surface of the medium, the propagation direction remains unchanged. When light is obliquely incident from the air into the water, the refraction angle is smaller than the incident angle.

At normal incidence, the propagation direction remains unchanged.

Infrared application: infrared remote control, strong thermal effect and strong infrared penetration.

Application of ultraviolet ray: fluorescence effect, physiological effect and chemical effect.