Question

Part 1 Specular Reflection:

Take a piece of fresh aluminum foil straight form the roll. You should be able to notice that one side is “shinier” than the other. When held flat, you can just make out your reflection in the shiny side of the foil.

The material is the same in both cases. Why do you see a reflection in one side, but not the other?

Now, crumple up the foil into a ball and then stretch it back out flat again. Can you still see yourself in the shiny side? Why, or why not?

The reflective surface in a bathroom mirror is not the glass, but a thin layer of silver on the back side of the glass. What must be true about this thin layer or silver for you to see a clear reflection of yourself.

Answer 1

1) Aluminum foil is produced by rolling it between successive steel rollers. Each set of rollers squeezes the foil thinner. The last stage of rolling reduces the foil's thickness to a thousandth of an inch or even thinner. The problem is that such a thin foil is too easy to tear during the last rolling stage. So, for the last stage of rolling, two sheets of foil are placed face to face and passed though the final set of rollers together. Since the steel rollers are highly polished, the foil faces that contact the rollers are also embossed to a highly shiny surface.After rolling, the resulting sheets are separated from each other. The surfaces of each foil that had faced each other are matte in texture, since they had only been squeezes against each other, and not the polished rollers.Also, the shiny surface of the foil should reflect more radiation than the dull surface, which will be better able to trap incoming waves rather than reflect them back.

After crumpling the foil, we won't be able to see our reflection on either side because the crests and troughs will reflect the light back.

2) When you stand in front of a mirror, what you see is the conservation of energy in action, working its magic on light. Light is energy traveling at high speed (300,000 km or 186,000 miles per second) and, when it hits an object, all that energy has to go somewhere. There are three things that can happen when light hits something: it can pass through (if the object is transparent), sink in and disappear (if the object is opaque and darkly colored), or it can reflect back again (if the object is shiny, light-colored, and reflective). Either way, the conservation of energy is at work: there is just as much energy around before light hits something as afterward, though some of the light may be converted into other forms.

The silver atoms behind the glass absorb the photons of incoming light energy and become excited. But that makes them unstable, so they try to become stable again by getting rid of the extra energy—and they do that by giving off some more photons. The back of a mirror is usually covered with some sort of darkly colored, protective material to stop the silver coating from getting scratched, and also to reduce the risk of any light seeping through from behind. Silver reflects light better than almost anything else and that's because it gives off almost as many photons of light as fall on it in the first place. The photons that come out of the mirror are pretty much the same as the ones that go into it.