# Parabola - An Optical property

- Author:
- Simona Riva

- Topic:
- Geometry, Parabola, Reflection

Light reflects off a curved surface by forming

*equal angles*(*incidence*and*reflection*)*with the tangent*at the point it falls on the surface. If we consider a parabola as a reflecting surface, when a*ray of light emitted from the focus*meets a*point on the parabola*, it will*reflect*off in a*straight line parallel to the axis of the parabola*. The converse also holds, and it's the principle used - for example - to design satellite dishes: any*ray parallel to the axis*of the parabola will*reflect*off the parabola and*pass through the focus*. Start the animation in the applet below to view this optical property of parabolas. If you**Show details**, you will see the geometry behind this property: move the point of incidence to verify that the property holds for all points of incidence on the parabola.