The charged particles are electrons, which are attracted to a positively-charged plate. When they strike this plate, they give off more electrons, which strike other plates. Eventually, there are enough electrons to produce a measurable electric current, which can be amplified so that the sound is heard through a speaker. The following diagram shows how this works. Considering the different arguments for light as a wave or as a particle, perhaps the most informative thing we can do is to simply describe light in terms of what it does.
Part is reflected from the front surface and part from the rear.
Why this happens is unknown. The following shows how light moves in water. These properties of light explain why we see certain phenomena. An oil slick is like an uneven sheet of glass. Colors are seen because red light is slower than blue light.