| MadSci Network: Physics |
Dear McGirls,
When I was a youngster, I was just as intrigued by the things you see when you look into a hollow (concave) or bulging (convex) mirror, as exemplified by your well-polished silver spoon.
I used to look for explanation in books, and always found the same "ray-tracing" schemes, which we later also had at school. They distinguish, among other things, between virtual and real images. But I didn't understand them, and I fear you wouldn't, either. Otherwise you would have found the answer in a book by now. So I try to answer your question in a less scientific, more "heuristic" way.
Let's start with an ordinary, flat mirror, placed vertically in front of you. Of course, in it, you see your image the right way up. This means, when you direct your gaze straight ahead, you see your head. When you look down, you see your feet. Now incline the mirror towards you. Look straight ahead. What do you see? Your feet.
On the other hand, if you tilt the mirror back away from you, you must look down in order to see your head. Now I make a crude approximation of a hollow mirror, replacing it with just two flat mirrors, one above the other, and touching each other at the border. The upper one is inclined towards you, the lower the other way round. In reality, the hollow mirror should be approximated by an infinite number of flat mirrors with gradually changing inclination. But the principle works with just two: If you look straight ahead, you see your feet, if you look down, you see your head. In other words, the arrangement turns you upside down by pieces.
By the way, this only works, if you are at a certain minimum distance from the mirrors. The same is true for the hollow mirror. If you put e.g. your finger rather close to the spoon, you see its image right side up and enlarged. In order to "model" the bulging side of the spoon, you just reverse the inclination of the two mirrors, i.e. the top one is inclined backwards, the bottom one forward. As you can see, your head is reflected by the upper mirror, and you have to shift your gaze only by a small angle to see your feet: the image is reduced.
To make more interesting observations, you should get yourself an oldfashioned shaving mirror and some lenses from a disused projector.
I wish you a lot of fun
Werner Sieber