•Column Editor’s Note: In last month’s “Little Gem,” Marshall Ellenstein showed us how “magic sunglasses” could be used to illustrate that no matter how far or close to a plane mirror, one sees the same amount of one’s image. Distance doesn’t make a difference. This month’s column examines additional ways to demonstrate this simple yet fascinating phenomenon.

A chance observation in a room with a mirror leads to suggestions for classroom activities. Figure 1 shows the situation of two identical lamps A and B in a room. MM is a mirror on the wall behind lamp B. Observing from a viewpoint beside lamp A, the image of A in MM has a size simply related to lamp B. It appears to be half the size of B.

Figure 2 is a photograph showing what is observed with an equivalent setup. The camera captures its own reflection.

The eye judges the...

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