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

reflection: incident ray and reflected ray matching angle

Angle In Matches Angle Out

Or in more mathematical language:

Angle of Incidence  =  Angle of Reflection
The Law of Reflection

Another example:

reflection: incident ray and reflected ray matching angle



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

Angles are measured from the Normal.


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

reflection mirror makes virtual image
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:

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

And we get this:

reflection mirror curved makes upside down virtual image
Our puppy sees an upside down reflection!

Just like the inside of this spoon:
spoon reflection

And what about this wonderful shape:

cloud gate reflection
Cloud Gate in Chicago


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.

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

telescope bure plateau
Incoming radio waves get sent to the focal point for detection.
Plateau de Bore Radio Telescope


An echo is a reflection, usually of sound from a hard surface.

echo clap
As well as hearing it directly, the sound of this clap
is also heard a short while later from the wall

Other types of waves can have echoes, such as radio waves.