Eli5: How Plane mirror can show full image of the object when the size of the given mirror is half of the height of that object ?



[HERE PHOTOS](http://imgur.com/a/cZVtL6i)

In: Physics

Mirrors reflect the photons of light that hit them. They don’t crop/manipulate the image coming in, merely they just send it back. If something very large has light bouncing into a small mirror, the mirror will reflect that light away, into your eyes.

The “size” of an object decreases the farther away it is; you can see this by holding your thumb up to your eye and blocking all your sight versus holding it at arms length and only blocking a tiny bit of your sight.

A mirror reflects light to show you an image of the object. However, since the light has to travel from the object to the mirror to your eyes, it will appear farther away than it actually is, either to you or the mirror. Farther away means that the object appears smaller. So even with a small mirror, you can see the whole object if you are the correct distance from it.

When light hits a mirror it reflects at the same angle it came in on. Think of photons like a que ball that bounces off a rail perfectly.

One implication of this is that if you shine a light from some plane to a mirror parallel to that plane the light will reflect off the mirror on a spot exactly between where you shone the light from and where it returns to the plane.

If you stand a plane mirror in front of you the light that reaches your eye from your foot hits the mirror half way up from your foot to your eye. The light from the top of your head that reaches your eye hits the mirror half way between your eye and the top of your head. Light from any other part of your body that reaches your eye will reflect off the mirror somewhere between those two. You don’t need any mirror outside that area.

A mirror will make a virtual image that you can look at *behind* the mirror, at a distance behind it equal to the distance between you and the mirror. Twice the distance means half the angular height. Imagine a triangle going between you and the edges of the mirror. Now move the mirror twice as far away and extend the triangle to that new distance: the corners of the triangle are now twice as far apart as the edges of the mirror. So you could use half the mirror, and still not clip off any of the image.

If you point a mirror in the right direction, you can see the entire moon reflected in a small hand mirror. The moon is huge! The hand mirror is small. But the entire moon is visible in the mirror because you are close to the mirror, and the moon is far away. Far away things look small.

To be exact, how big something looks is inversely proportional to how far away it is. That means, if two objects are the same actual size, but one is twice as far away, the far away one will look half as big. If it’s three times as far away, it looks one-third as big, and so on.

When you look at something in a mirror, the “viewing distance” is both the distance between you and the mirror, plus the distance between the mirror and the object. So when you look at yourself in a mirror, the “viewing distance” is twice the distance between you and the mirror. That means the “you” that you see in the mirror is twice as far away as the mirror, so it looks half as big. Thus, even if you are twice as big as the mirror, the “you” that you see in the mirror gets shrunk in half, which would fit in the mirror.

OK say your mirror universe twin is on the other side of the mirror there. So the mirror acts like a window into the mirror universe. Does the window have to go all the way to the ground for you to see your mirror twin’s shoes?