The law of refraction of light: three lines * * * plane, two lines are separated, and the refraction angle is less than the incident angle.
Snell's law
When light refracts through the interface between two media, it is one of the basic laws of geometric optics to determine the relationship between the propagation direction of incident light and refracted light. The plane formed by the incident light and the interface normal passing through the incident point is called the incident plane, and the angles between the incident light and the refracted light and the normal are called the incident angle and the refraction angle respectively, which are expressed by θi and θ T. The refraction law is as follows: ① The refracted light is in the incident plane. ② The ratio of sine of incident angle to refraction angle is a constant, which is expressed by n2 1.
Where n2 1 is called the relative refractive index of the second medium to the first medium.
Ptolemy, a Greek in the 2nd century A.D., was the first to study refraction quantitatively. He measured the correspondence between incident angle and refraction angle when light refracted from air into water. Although the experimental results are not accurate, he is the first person to study the law of refraction quantitatively through experiments. 162 1 year, the Dutch mathematician W. Snell accurately determined the law that the ratio of cotangent of incident angle and refraction angle is constant through experiments, namely
So the law of refraction is also called Snell's law. 1637, French R. Descartes published the modern sine ratio law for the first time in his book Refractive Optics. Like the reflection law of light, the refraction law preliminarily determined by experiments can be proved according to Fermat principle, Huygens principle or electromagnetic theory of light.
The above refraction law of light only applies to static interfaces composed of isotropic media.
law of refection
When light is reflected on a smooth interface, the law that determines the propagation relationship between reflected light and incident light. One of the basic laws of geometric optics. As shown in the figure, the plane formed by the incident light IO and the interface normal ON at the incident point O is called the incident plane, and the propagatiON directions of the incident light IO and the reflected light OR can be represented by their included angles θi and θr with the normal on, respectively. θi and θr are usually called incident angle and reflection angle, respectively. The law of reflection is as follows: ① Both reflected light and incident light are in the incident plane. ② The reflection angle is equal to the incident angle, that is, θ i = θ r. The above reflection law only applies to the interface of isotropic media, and only solves the problem of light propagation direction, but not the problem of energy distribution during reflection. The reflection of light is very similar to the rebound of an elastic ball on a smooth desktop in mechanics. I Newton once proved the law of over-reflection according to the particle theory of light (see the duality of light).
The law of light reflection was originally obtained from experiments, which can be proved according to Fermat's principle, geometrically from the viewpoint of light fluctuation by Huygens' principle (see huygens-fresnel principle), and theoretically from the boundary conditions of electromagnetic field.