Reflection Property of a Parabola

This applet demonstrates the reflection property of a parabola. Vertical lines parallel to the axis are reflected to the focus, and vice versa. This property is the basis of the design of flashlights, headlights, satellite dishes, reflecting telescopes, etc.

Instructions: Drag point B along the parabola. You can also change the shape of the parabola by using the slider in the lower left corner.

Michael Butler and Bruce Wagner, Created with GeoGebra