Reflection: Angle of Incidence, Curved Surfaces & Diffusion

Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

How does light bounce off surfaces? Learn the differences between how light bounces off flat surfaces, curved surfaces, and non-shiny surfaces. Then reflect on your reflection knowledge with a quiz.

What Is Reflection?

Reflection is the bouncing of light waves off a surface. This can include visible light or other parts of the electromagnetic spectrum, such as infrared or ultraviolet light. There are also lots of ways light can reflect off a surface, but the basic principles are the same.

Reflection is a part of everyday life. If light didn't reflect, we wouldn't be able to see anything - light has to bounce off of objects to reach your eyes. And that says nothing of when you look in a mirror, which of course wouldn't work at all without reflection. Today we're going to talk about the exact way that light reflections, and how that applies to different kinds and shapes of surfaces.

Law of Reflection & Curved Surfaces

The law of reflection is a basic physical law that explains all kinds of reflection. The law of reflection says that the angle of incidence is equal to the angle of reflection. Or in less technical language, the angle at which light hits a surface (angle of incidence) is equal to the angle at which light bounces away from the surface (angle of reflection). Thus light bounces symmetrically from surfaces.

Law of Reflection
Law of Reflection

This law applies to everything, even though sometimes it might not seem like it. It's easy to see how the law of reflection works with mirrors, but what about curved surfaces?

It turns out that it even works for curved surfaces. To understand this, you have to realize that at the exact point the light hits the curved surface, the surface is facing a particular direction. You can see that direction by drawing a tangent to the curved surface. If you look at the way light bounces off that tangent, it's exactly the same as if it was hitting a flat mirror facing that direction. So the law of reflection really works.

Reflection From a Curved Surface
Reflection From a Curved Surface

Diffuse Reflection

So that's what happens with flat and curved mirrors, but what about non-mirrored surfaces. How does light bounce off everyday, dull objects?

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