So what exactly do you see in a mirror’s reflection? We can find out by putting together everything that we have learned so far. We start by figuring out the path the light ray travels in forming an image. If we have a flat horizontal mirror and hold a banana above it then the light rays from the banana to our eye travel paths that look like

The red paths are the real light rays from the banana to our eye. I’ve only shown a few of the (infinitely) many rays used to form the image. When we see the light from the banana it looks like it came from behind the mirror because it bounced off the mirror in a straight line according to the the law of reflection. This makes it look like the light first traveled an imaginary path (called a virtual path because its not real) to the mirror instead of the real path to the mirror. These virtual paths are indicated by the dotted purple lines in the above image.

By lining up the paths we see that the path from the top of he real banana corresponds to the bottom of the virtual banana. If we do this for all the light rays we notice the the final result is that the banana mirror image is upside down or as we mentioned earlier it is inverted. This is why mirror images appear inverted and why the words in a mirror appear backwards.

Whew, that’s a long explanation.You were introduced to a lot of new and important concepts in physics. Don’t worry if you don’t understand it all now. Just think about it for awhile and if you still don’t understand something ask me and I’ll try to give you a shorter answer.

[As a final aside I'll mention that inversion is a property of every mirror including curved mirrors. Most modern telescopes use curve mirrors to see the Universe. Thus most telescopes also invert their images so when you look through a telescope you have to aware of this fact. Note; if you use two mirrors then you get two inversions and two inversions produce the same result as no inversions. Astronomers don't like to do this because every time you bounce some light of a mirror or pass the light through a lens you lose some of the light so so cannot see as much of the sky. As a result telescopes tend to be made with as few mirrors and lenses as possible.]

Well, this has been a fun question to answer. If you have any more questions send them to me.

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