Teaching Physics with the Physics Suite

Edward F. Redish

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Where can you see the bulb?*

In the following diagram, M is a plane mirror; B is a very small bright light bulb that can be treated as a point source of light; and H is an opaque housing that does not transmit light. An observer can stand anywhere along a line O to try to see the image of the light bulb in the mirror.

By using relevant rays of light, determine those locations along the line O from which the image of B is visible and those locations from which it is not visible. Marke the regions along line O accordingly and explain the reasoning you used in drawing the rays.

* From [Arons 1990].

Note to the instructor: Tracing rays in order to figure out where you can see an object is harder for many students than one would think. This is a good example and Arons has others as well. The "Light and Shadow" Tutorials in [Tutorials 1998] deal with this issue effectively.

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Page last modified October 31, 2002: OP09