物理系统由于某些原因而要发生突变时所处的状态 ,叫做临界状态 .突变的过程是从量变到质变的过程 .在临界状态前后 ,系统服从不同的规律 ,按不同的规律运动和变化 .如光学中折射现象的“临界角”、超导现象中的“临界温度”、核反应中的“临界体积”、光电效应中的极限频率、? The state in which the physical system has to undergo mutation for some reason is called the critical state. The process of mutation is the process from quantitative change to qualitative change. Before and after the critical state, the system obeys different laws and moves and changes according to different laws. For example, the “critical angle” of the refractive phenomenon in optics, the “critical temperature” in superconductivity, the “critical volume” in nuclear reactions, the limit frequency in the photoelectric effect,