Reflecting on Reflection

Ah, on to the next topic now. Go ahead and take a seat, but take this mirror with you. You're going to want it as we study... dun dun dun... Reflection!

Before we begin, I'd like you to look in that mirror I gave you. Looking back is, well, you! Now smile... wave with your left hand... wave with your right hand. Good, just like that. What did you notice? Yes, you're correct! When you smile, nothing really seems to change. But when you wave with your left hand, the image of you waves with its right hand and when you wave with your right hand, it waves with its left! Funny little thing, reflection is. It seems confusing now, but don't worry. Soon you'll understand perfectly!

The first you thing you need to know is that when a wave is reflected there is no change in its speed, frequency, or wavelength. The only difference between the incoming wave and reflected wave is that they are inverted! I'll show you what I mean.


http://www.acs.psu.edu/drussell/Demos/reflect/reflect.html

You see, on the way to the barrier, the wave is going up, but after it hits the barrier and turns around, the wave is going down. The entire time the wave is perpendicular to the barrier.

But what if the wave and the barrier aren't perpendicular to each other? Great question! First, look at this diagram.


http://aplusphysics.com/courses/regents/waves/images/law-of-reflection.gif

This picture shows us the Law of Reflection. This law states that the angle in which the incoming ray, or incident ray, hits the reflecting surface, is equal the the angle in which the reflected ray leaves. The angles are measured from the "normal line" which is perpendicular to the reflecting surface. This is true for any wave that is being reflected off of any surface at any angle. Don't forget it!

A bit more tricky to understand are concave and convex barriers. But don't you fret, by remembering the Law of Reflection, you'll get it in no time!

When straight waves crash into a concave barrier, the waves reflect off of the barrier at the same angle that they came in at each individual point (Ahem, the Law of Reflection).  Here's where it gets interesting: instead of being straight waves, the waves are now circular because concave barriers curve inwards! Also, every wave is reflected to a common point called the "focus point." It must be magic you say? Naw, it's just physics!

Another interesting fact about the focus point: if circular waves start at the focus point and hit a concave barrier, they reflect off as straight waves!

Why yes, you're right! You're really thinking on your feet now. Spoons are concave! Why are you upside down in the reflection on a spoon? I think this picture can briefly help you to understand, now that you know a bit more about reflection.

http://blissfullydomestic.com/wp-content/uploads/mirrors-concave-1-300x140.jpg

Also concave are satellite dishes. The straight waves come down and hit the dish in all different locations. The waves are then reflected off of the dish and are, well, focused to the focus point which then sends the waves to your tv!

Convex barriers reflect waves in a very similarly as concave barriers. The Law of Reflection still applies, of course. But since the barrier is curved outwards, the reflected waves are all directed out. However, there is still a focus point! This time, it's on the other side of the barrier. If you were to extend the waves through the barrier, they would all meet at this focus point.

"OBJECTS IN MIRROR ARE CLOSER THAN THEY APPEAR" Have you seen that before? Well duh! If you've ever driven in a car you definitely have! Mirrors on the passenger side of a car are convex. Since the focus point is "inside" the mirror, the image is also created inside. The image also appears smaller because the rays are being pushed closer together.

http://blissfullydomestic.com/wp-content/uploads/mirrors-convex-1-300x137.jpg

Look at all this wave stuff affecting your every day life!