The reflective property of the ellipse

Imagine that the elliptical shape below is a reflective surface, and imagine that a light source is placed at one of the foci.

Click on several points on the ellipse to see how rays of light emitted from the focus are reflected, then answer the question below.

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What do you notice about the reflected rays?

Each of the reflected rays passes through the other focus.

Whispering chambers are rooms with special acoustic properties. Some whispering chambers are built in the shape of an ellipse. When conversation occurs near one focus of the ellipse the sound waves are reflected from the walls to the other focus allowing someone positioned at the other focus to eavesdrop on the conversation.

A whispering gallery at St. Paul's cathedral