AL phy問題

以A Level 程度黎講, 我只可以同你講 mechanical wave, the explanations are as follow,

As the wave pulse approaches the fixed end, the internal restoring forces which allow the wave to propagate exert an upward force on the end of the string. But, since the end is clamped, it cannot move. According to Newton's third law, the wall must be exerting an equal downward force on the end of the string. This new force creates a wave pulse that propagates from right to left, with the same speed and amplitude as the incident wave, but with opposite polarity (upside down).

For EM Wave, bery complicated maxwell equations are involved, if you really want to know, just let me know

it is beyond a level, must use maxwell equation to solve