Mr. Z’s “Waves” Unit

Describe what happens to a wave when it moves from one medium to another AIM: How are wavers refracted?

Refraction AIM: How are waves refracted?

What is a wave is? energy moving place to place. What is the law of reflection? the angle of incidence equals the angle of reflection ” AIM: How are waves reflected?

What is “The normal”? is an imaginary perpendicular line “drawn” to calculate the angles of reflection and incidence AIM: How are waves reflected?

Refraction: Refraction is what happens to light rays that enters into one transparent material from another material of different density AIM: How are waves refracted?

Refraction: Refraction is the bending of waves as it moves from one medium to another AIM: How are waves refracted?

Refraction: Waves bend when they change mediums because the different densities of each medium cause the light to change speed. This change “of the speed of the wave” is what causes refraction. The Greater the density of the medium, the slower the speed of the light wave!

Laws of Refraction: #1: When a light wave moves at an angle from a less dense medium to a more dense medium, the wave will slow. As a result it bends towards the normal AIM: How are waves refracted?

Laws of Refraction: #2: When a light wave moves at an angle from a more dense medium to a less dense medium, the light wave will speed up. As a result the wave bends away the normal AIM: How are waves refracted?

Laws of Refraction: #3: When a wave moves from one medium to another along the normal (in a perpendicular fashion), there is no refraction although the light wave will still change speed. AIM: How are waves refracted?

© 2002 The Physics Classroom and Mathsoft Engineering & Education, Inc. All rights reserved. This is an example of Refraction

Waves travel at different speeds in different materials. The change in speed is what causes the wave to bend. © 2002 The Physics Classroom and Mathsoft Engineering & Education, Inc. All rights reserved.

This is an example of Refraction

Waves do not refract if they at a perpendicular angle. But if a wave crosses the barrier at any other angle, the wave will bend as they go through it. © 2002 The Physics Classroom and Mathsoft Engineering & Education, Inc. All rights reserved.

We are able to see because light from an object travels to our eyes. © 2002 The Physics Classroom and Mathsoft Engineering & Education, Inc. All rights reserved.

Every object that can be seen is seen only when light from that object travels to our eyes. © 2002 The Physics Classroom and Mathsoft Engineering & Education, Inc. All rights reserved.

Why can you see Mary in class?. As you look at Mary in class, you are able to see Mary because she is both illuminated with light and that light reflects off of her and travels to your eye. © 2002 The Physics Classroom and Mathsoft Engineering & Education, Inc. All rights reserved.

As light travels through a given medium: 1. it travels in a straight line. 2. when light passes from one medium into a second medium, the light path bends 3. Refraction takes place. 4. The refraction occurs only at the boundary.

5. Once the light has crossed the boundary between the two media, it continues to travel in a straight line 6.Only now, the direction of that line is different. © 2002 The Physics Classroom and Mathsoft Engineering & Education, Inc. All rights reserved.

ANALYZE this Diagram

A pencil was submerged in water and viewed from the side. As you looked at the portion of the pencil located above the water's surface, light travels directly from the pencil to your eye. Since this light does not change medium, it will not refract. © 2002 The Physics Classroom and Mathsoft Engineering & Education, Inc. All rights reserved.

As you look at the portion of the pencil which was submerged in the water, light has traveled from water to air (or from water to glass to air). This light ray changed mediums.

This light ray changed mediums and subsequently underwent refraction. The light began to travel faster as it moved from the water to the air. As a result, the image of the pencil appears to be broken.

Furthermore, the portion of the pencil which is submerged in water appears to be wider than the portion of the pencil which is not submerged. This is more refraction!

© 2002 The Physics Classroom and Mathsoft Engineering & Education, Inc. All rights reserved. Let’s examine Mr. Z’s technique for catching dinner. Will he be successful?

Because of the refraction of light, the observed location of the fish is different than its actual location. © 2002 The Physics Classroom and Mathsoft Engineering & Education, Inc. All rights reserved.

Copy this diagram and indicate where Mr. Z has to throw his spear to catch the fish. © 2002 The Physics Classroom and Mathsoft Engineering & Education, Inc. All rights reserved.

Should Mr. Z aim above or below where the fish appears to be in order to bring home dinner? © 2002 The Physics Classroom and Mathsoft Engineering & Education, Inc. All rights reserved.

Normal © 2002 The Physics Classroom and Mathsoft Engineering & Education, Inc. All rights reserved. Let’s find out what Mr. Z has to do!

Light from the fish travels from the water through the air, and then into your eye Air is less dense then water, so light refracts away from the normal. Normal

The fish is actually located at the blue line. But because of refraction, its image is bent away from the normal towards the “brown” colored line. Normal

The light from the fish refracts away from the normal, giving the impression that the fish is located straight along the “brown line”, when in reality it is much closer to the fisherman (as indicated in blue). Normal

Fortunately for the fish, light refracts as it travels FROM the fish in the water TO the eyes of the hunter. The refraction occurs at the water-air boundary. Due to this bending of the path of light, the fish appears to be in a location where it is not. © 2002 The Physics Classroom and Mathsoft Engineering & Education, Inc. All rights reserved.

Subsequently, the hunter launches the spear at the location where the fish is thought to be and misses the fish. © 2002 The Physics Classroom and Mathsoft Engineering & Education, Inc. All rights reserved.

Of course, the fish are never concerned about such hunters They know that light refracts at the boundary and that the location where the hunter is sighting is not the same location as the actual fish. How did the fish get so smart and learn all this? © 2002 The Physics Classroom and Mathsoft Engineering & Education, Inc. All rights reserved.

FST = Fast to Slow, Towards Normal If a ray of light passes across the boundary from a material in which it travels fast into a material in which travels slower, then the light ray will bend towards the normal line. SFA = Slow to Fast, Away From Normal If a ray of light passes across the boundary from a material in which it travels slow into a material in which travels faster, then the light ray will bend away from the normal line.

AIM: How are waves refracted?

Class Activity: W/S Concepts 7-4

Homework: INTERNET QUESTIONS