How thick does a material have to be to start to become opaque to light?

Question

anonymous · Answer

This doesn't depend on how thick a material is because that could vary for different materials. If you are talking about light in general and not just gamma radiation; if the frequency of the light is low enough, it can pass through any material, this brings us to why some things are transparent. The reason is that the photon will not have enough energy to move an electron to a higher energy state and get absorbed, therefore it will just pass through the object and the photon also needs higher energy to do this(higher frequency means higher energy). for more information look at this video: https://www.youtube.com/watch?v=Omr0JNyDBI0