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虹是由阳光经雨云中的无数个水滴产生的色散现象,其中每一个水滴都如同一个小棱镜,它们对阳光的反射和折射光路如图1所示.以主虹为例,它是阳光经水滴的两次折射、一次内反射而形成的.由折射定律,sini/sinr=n (1)再由图中的几何关系可以得到:φ=4r-2i (2)可以证明,对于确定折射率n的介质折射光线都存在一个最大偏向角φ _(max),或者说存在相对阳光的入射方向有最小偏向角180°-φ(max)经计算φ_(max)的值为
The rainbow is the dispersion phenomenon caused by the numerous droplets of sunlight passing through the rain cloud. Each of the droplets acts like a small prism. Their reflection and refraction of the sunlight is shown in Figure 1. Take the main rainbow as an example, it is sunlight. The water droplets are formed by two refractions and one internal reflection. From the law of refraction, sini/sinr=n (1) and then the geometric relationship in the figure can be obtained: φ=4r-2i (2) It can be proved that for determining the refraction There is a maximum deflection angle φ _ (max) for the media refracted light of rate n, or there is a minimum deflection angle of 180°-φ(max) with respect to the incident direction of sunlight. The value of φ max is calculated.