在复习初三“光的初步知识”一章后,学生提出了如下的问题;一块平面镜垂直插在水中,如图1所示,一束光线恰好射在平面镜与水接触的转角点。请画出反射光线,并说明理由。我请教了两位大学老师,他们对以上问题有下面两种不同的解答,启人深思。现将问题解答另述于后。第一种解答认为:“图1上所画的一根入射光线,在物理上是无法实现的,它仅作为一束光线的‘缩画’才有意义。临界光线可能一分为二,这在菲涅耳双面镜、双棱镜之类的装置中已有先例。具体解法如图 After reviewing the chapter “Introduction to the preliminary knowledge of light” in the third year, the student asked the following question; a plane mirror was inserted vertically in the water. As shown in Fig. 1, a beam of light just hits the corner point where the mirror is in contact with water. Please draw a reflection of light and explain why. I consulted two university teachers who had the following two different answers to the above questions. The problem is explained later in the post. The first kind of solution states that: "An incident light beam drawn on Figure 1 is physically unachievable, and it only makes sense as a ’reduction’ of a light beam. The critical light beam may be split into two. There are precedents in devices such as Fresnel mirrors and double prisms.