12.5 Total Internal Reflection

12.5 Total Internal Reflection

Today in class we learned about total reflection. This is when we cannot see the refracted image, and only see the reflected image. Here is example of it occurring in real life.

We get total internal reflection when the angle of incidence is either at or greater than the critical angle. The critical angle is the angle of incidence that results in an angle of refraction of 90^º. For example the critical angle of water is 49^º. This means that if you have an incident ray of 49^º or higher, total internal reflection will occur. Like everything in life conditions must be met for this to work. The 2 conditions are that light must be travelling more slowly in the first median than in the second, and the angle of incidence is large enough that no reflection occurs. There is a diagram showing how this works. 

There is an easy and simple way to figure out the critical angle, without just experimenting for who knows how long. You simply use Snell's general equation we learned. In this case the angle of refraction is 90^º making sin0R=1^.n₁ would be the more refractive medium, and n₂ would be the less refractive median. You are looking for the critical angle or 0C (angle of incidence) the formula will look a little like this.

Diamonds are an excellent example of total internal reflection, because that is what causes them to sparkle. They have a very small critical angle of 24.4^º. This means that most of the light hitting is undergoing total internal reflection. Since diamonds are cut in a very specific way, light rays will bounce around inside the diamond before exiting, this causes the diamond to Sparkle!

Another way that total internal reflection is used daily is in fiber optics. Critical angles and total internal reflections are the only reason this works. Fiber optics is used in the communications industry for phones, computers, TV's, etc. They are also used in many other places such as in movies, in automotive, and in medical technologies. They are important in these respective fields to shine a light so that we can learn and find out more. If you are interested in fiber optics and want to learn more go to, http://en.wikipedia.org/wiki/Fiber-optic_communication

If you still don't fully understand the concept of total internal reflection you may want to check out these links: http://www.physicsclassroom.com/class/refrn/u14l3b.cfm

http://www.youtube.com/watch?v=dqCEMUot_lY

Also if you want to see a really cool demonstration of total internal reflection, click on this link, http://www.youtube.com/watch?v=s7w1Z1FCgwA

By: S.R and A.K