On the previous page,
we assumed that the light rays approaching the mirror
were all parallel. This is true for a distant object, but
not true for an object a finite distance removed from the
mirror. We now derive the point at which the light is
collected, the The similarity of the triangles allows one to write One can combine these two equations, eliminating the ratio of the object and image heights, to obtain a relationship between the distances and focal length. This is a remarkably useful formula. The same formula will be used for both concave (above) and convex mirrors as well as lenses. |