I was reading "QED" by Richard Feyman. I understand the method they used to calculate the possibility of partial reflection. But there is one thing that I just can't stop myself from thinking about it, (in the book, they say that the phenomenon of partial reflection can easily be explained by the wave theory of light. (the wave theory collapsed after the developed of instrument that can detect a single photon was invented.)

 

My question was how was the partial reflection easily explained by the wave theory of light?

 

(All that the book had mention was that wave can combine or cancel out, thus explained the partial reflection phenomenon.) But, how did that explain?

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by the way, QED= quantum electrodynamics

Applying the boundary conditions to the wave equation give a transmitted and reflected wave. You'll find that not all of the wave can be transmitted, except under very specific conditions, so a reflected wave must exist.