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

12.7 Phenomena Related to Refraction

12.7 Phenomena Related to Refraction

Apparent Depth

Figure 1.0

Apparent Depth is the depth that an object appears to be at due to the refraction of light at the transparent medium. Our eyes interpret the refracted light as coming from a source along the line of sight. An example would be cleaning a fish tank. When you put the net in to the water to remove the fish, more times than not, you will miss the fish, because, the object is travelling from a less dense medium to a denser medium, it will result in refraction, causing a virtual image, and the net to be bent. (The light is bending towards the normal.) Therefore the fish is appeared to be deeper than it actually is. (see Figure 1.0)

Mirages

A mirage is a virtual image that forms as a result of refraction and total internal reflection within the Earth's atmosphere. Light waves from the sun travel straight through the atmosphere to our eyes. However, light travels at different speeds through hot and cold air. Mirages occur when the ground is hot, and the air is cool. For example; in the desert, the hot sand warms a layer of air just above the ground. When light moves from the cool air medium in to the hot air medium- it is refracted- and therefore bent. The "puddle" that we see appear on the ground is the reflection of the light bending (refraction) from the sky. Therefore the light from the sky appears to be on the ground in front of us, which creates the image of a puddle. See the video provided below, for an in depth explanation.

 Dispersion of Light and Rainbows

Dispersion is the separation of white light into its constituent colours (the spectrum.) Each colour of visible light (ROYGBIV) travels at different speed when it travels through glass prisims. That is why light refracts more than the other colours of the spectrum. Red light is refracted the least of all the colours in the spectrum. This is how rainbows are created in glass prisms. (See Figure 1.1) The video provided below will explain this concept in greater detail.

Figure 1.1

When white light enters a raindrop, dispersion occurs. The seven colours of the rainbow are produced. When this light hits the back of the raindrop, partial reflection occurs. The light continues to refract once it moves from the raindrop into the atmosphere. People only see 1 colour from each drop because the majority of the other colours miss our eyes. Therefore a rainbow is a mix of drops at different elevations. The shape of the rainbow comes from the different angles of refraction that the colours are producing. (See Figure 1.3) Double rainbows occur from two internal reflections, that are always higher in the sky compared to the original rainbow and the order of the colours are reversed. (See Figure 1.4)

Figure 1.4

Figure 1.3

For additional information go to:

Rainbows & Refraction

Phenomenas Related to Refraction

Bending Sunlight

By:  J.C. and M.T.