# Reflection

Waves bounce off a surface at the same angle they strike it:

Angle In Matches Angle Out

Or in more mathematical language:

Angle of Incidence  =  Angle of Reflection
The Law of Reflection

Another example:

The Normal is the direction directly away from the surface (at right angles to it).

Angles are measured from the Normal.

## Mirror

Here we see light bouncing off a mirror to create a "virtual image" that looks like the real image (but reversed):

Our puppy sees someone in the mirror.

## Curved Mirrors

What happens when light reflects off a curved surface? We can draw individual rays of light to find out!

Here is how to work out the reflection of a ray:

 Where the ray hits draw a line flat against the curve (called a "tangent line") The normal line is at right angles to that tangent line Angle in matches angle out either side of the normal line

And we get this:

Our puppy sees an upside down reflection!

Just like the inside of this spoon:

Cloud Gate in Chicago

## Parabola

The parabola is a special curved shape that takes any ray coming directly in and sends it to a single "focus" point:

This is useful for telescopes. They can have a large parabolic collection area that sends the radiation to one small detector.

Technicians stand in front of one segment of the James Webb Telescope's
"segmented parabolic reflector"

Incoming radio waves get sent to the focal point for detection.