What is light?

Light refers to the linear vibration of countless photons. When a photon collides with an electron elastically and vibrates in a certain direction, the photons on the same line vibrate immediately. Light is not the flow of photons, but countless photons vibrate in situ on the same straight line. For example, sound is not the flow of molecules, but the vibration of molecules in situ. The breeze will not affect the propagation of sound, and the photon flow will not affect the propagation of light.

Light is actually the vibration direction of photons, and it is an image description of the vibration direction of photons.

Parallel rays in the same direction have the function of correcting each other's directions, which is beneficial to the straight-line propagation of light.

Light classification

Light is divided into gamma rays, x rays, ultraviolet rays, visible light and infrared rays according to frequency.

Gamma rays have penetrating power, which can penetrate lead plates several centimeters thick.

X-rays will not deflect in the electromagnetic field, which means that X-rays are uncharged.

Visible light can cause people's vision. About 44% of sunlight is in the visible range.

Infrared rays have a thermal effect.

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Brightness refers to the physical quantity of light (reflection) intensity on the surface of luminous body (reflector).

Luminous flux refers to the amount of light emitted by a light source per unit time. Unit: lumen (lm).

100W incandescent lamp 1 sec gives off a luminous flux of about 1200lm.

Illuminance refers to how many lumens of light flow in the area of 1 square meter. Unit: lux (Lx).

The farther away from the light source, the lower the illumination.

The law of light motion

1. reflection

Reflection refers to the phenomenon that light returns when it meets the material interface.

The law of reflection, reflected light, incident light and normal line are in the same plane, reflected light and incident light are located on both sides of normal line respectively, and the reflection angle is equal to the incident angle. (Huygens 1690, Netherlands)

2. Refraction

Refraction refers to the phenomenon that light deflects from the interface between two transparent substances and enters the second transparent substance.

Law of refraction Refracted light is in the same plane as incident light and normal line, and refracted light and incident light are located on both sides of normal line respectively. (Huygens 1690, Netherlands)

Dispersion refers to the dispersion of light by frequency.

Dispersion law The refractive index of light is proportional to the frequency, and the higher the frequency, the greater the refractive index. (Wang Jingbo 2020)

diffraction

Diffraction refers to the deviation of light from the original straight propagation direction when it passes through the edge of an obstacle.

The reason of diffraction is that photons repel each other, resulting in alternating light and dark stripes.

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Interference means that two beams of light from the same light source interfere with each other to produce bright and dark stripes.

Only two coherent light sources with the same frequency, constant phase difference and consistent vibration direction can produce optical interference. The light emitted by two ordinary independent light sources cannot have the same frequency, let alone a fixed phase difference, so they cannot interfere.

The reason of interference is that photons repel each other, resulting in alternating light and dark stripes.

Relationship between interference and diffraction

Light rays pass through slits to produce diffraction fringes, and double slits produce interference fringes, which is the redistribution of diffraction fringes.