WAVE INTERACTIONS Describe 4 kinds of wave interactions Explain the relationship between angle of incidence and angle of reflection Compare and contrast constructive and destructive interference Predict how a wave will behave if it moves from air into water.

Interaction, Energy, & Change You have learned that a wave is a transfer of energy through a medium. When that wave interacts with objects of a different medium or with other waves there is a change in the wave’s energy. This interaction causes a change in the properties of the wave. In this section of Ch. 14 you will learn about those interactions and how waves are affected by them. READ ONLY

Reflection We all see reflections every day, when we look at ourselves in the bathroom mirror. How do reflections happen?

Reflection (cont) Reflection occurs when a wave bounces off a surface barrier normal incident wave #1 reflected wave #1 incident wave #2 reflected wave #2 Explanation on next slide Draw this diagram. i r

Reflection (cont) Incident wave - the incoming wave Angle of incidence - the angle between the normal and the wave (i) Normal - a line perpendicular (90 degrees) to the barrier Reflected wave - the wave that bounces off the barrier Angle of reflection - the angle between the normal and the reflected wave (r)(r) The angle of incidence (i) will always be equal to the angle of reflection (r)

Diffraction Diffraction is the bending of a wave due to interaction between the wave and the edge of an object. Point of land into the ocean Waves moving in toward the land When the waves strike the rock the speed and frequency of the waves does not change. However, the direction of the waves will bend around the point of rocks.

A diffraction problem for you to solve. Diagram and explain how you could be standing in an alley and know that a parade is coming down the street even though you cannot see the bands in the parade. I hope they talk about reflection and diffraction.

Refraction Water Beam of light Refraction is the interaction of waves when they are moving in one medium and change to another medium. When light goes from air to water it slows therefore the beam changes direction and becomes wider. * - the bending of a wave as a result of a change in speed.

What happens to the width of a beam of laser light if it passes through several different mediums ? AIR WATER PLASTIC GLASS AIR Why does this happen ? As the light waves change mediums their speed changes. The slower the light travels the wider the beam becomes.

Why do fish appear larger in the water than they do out of the water? Actual size of the fish Size the fish appears to you Incident rays Refraction (bending of light waves) Reflected waves traveling at the speed of light in water Refracted waves speed up as they leave the water

Interference Interference - the effect of two or more waves interacting with one another. Suppose that you are riding a jet ski on Lake Conroe and you meet another jet ski going in the opposite direction. What will happen when the wake from your jet ski meets with the wake of the other? See if you can diagram what you think will happen. Taking your thinking to a higher level. Here is your challenge.

Line along which waves meet Energy waves of RED jet ski. Energy waves of GREEN jet ski. Sum of the two waves This is an example of DESTRUCTIVE INTERFERENCE As two waves meet in opposite directions they will cause part of one another to be destroyed by absorbing portions of each other’s energy. The resulting wave will have less energy. TAKS

NOW! Since you are so much smarter than you were a few minutes ago, figure this out. What would the wave diagram look like if both jet skis were going in the same direc- tion, right behind one another with the second ski just to the left of the front one?

Energy of wave of RED jet ski. Energy of wave of GREEN jet ski. The resulting wave is the sum of the two interacting waves. This is an example of CONSTRUCTIVE INTERFERENCE As two waves interfere with one another and they are traveling in the same direction they will combine their energies, thus producing a larger wave. TAKS

Interference Explained Destructive Interference If you look at the wave diagrams for destructive interference you should notice that the crest of one wave is meeting the trough of another wave. When the crests and troughs interfere with one an- other the energies subtract from one another with the resulting wave being one with smaller energy or less amplitude. Constructive Interference If you look at the wave diagram for constructive interference you should notice that the crest of one wave meets the crest of the other wave. When the crests of two waves meet they combine by addition of their energies with the resulting wave being a wave with greater energy or greater amplitude.

Review Reflection - when a wave bounces off a surface or barrier. Diffraction - when a wave bends around the edge of an object. Refraction - when a wave bends because of a change in the speed of the wave. This happens when the meduim changes. Interference - when two or more waves interact with one another. DESTRUCTIVE INTERFERENCE is when the crest of one wave meets the trough of another wave. Result = smaller wave CONSTRUCTIVE INTERFERENCE is when the crests of two waves meet. Result = larger wave.

Here’s your Quiz !! 1. You are in the mountains and holler loudly. The echo heard when the mountains holler back at you is because of wave ____________. 2. True or False Depending upon the angle that a wave hits a sur- face, it may reflect at an angle different than the angle it hits. 3. When a wave bends around the edge of an object is has changed because of ________________. 4. A fish looks larger in water than it actually is because the light waves reflected off the fish change speeds when they get into the air therefore they bend. This bending is called _______________. 5. ________________ is when two waves interact with one another. 6. If the resulting wave from #5 is larger the waves have experienced ________________ ___________________. 7. The line perpendicular to the surface of a reflected wave is called the __________________. 8. True or false When waves interact energy will always change. -12 pts for each X

Here’s your Quiz !! 1. You are in the mountains and holler loudly. The echo heard when the mountains holler back at you is because of wave ____________. 2. True or False Depending upon the angle that a wave hits a sur- face, it may reflect at an angle different than the angle it hits. 3. When a wave bends around the edge of an object is has changed because of ________________. 4. A fish looks larger in water than it actually is because the light waves reflected off the fish change speeds when they get into the air therefore they bend. This bending is called _______________. 5. ________________ is when two waves interact with one another. 6. If the resulting wave from #5 is larger the waves have experienced ________________ ___________________. 7. The line perpendicular to the surface of a reflected wave is called the __________________. 8. True or false When waves interact energy will always change. reflection diffraction refraction Itreecnefrne Interference constructive interference normal -12 pts for each X