(this experiment is to be used with the Waves lab from SPECS)

Waves play such an important role in our lives and most of us very rarely pay any attention to them. Without waves we would know very liitle about the world around us. Sound and light are waves, in fact all electromagneic radiations are waves. These electromagneic radiations include radio waves, microwaves, visible light, x-rays and so on. Therefore, the more you know about waves the more you know about the world around us.

Purpose

The purpose of this activity is to give you the chance to "see" and explore the interaction between two waves. In your everyday life you have probably experienced this type of interaction many times. This activity will allow you to control the interaction and help you to visualize what happens when two waves meet. How does their interaction effect the way you view your surroundings?

Words you should know

amplitude, constructive interference, destructive interference, diffraction, frequency, fundamental frequency, phase angle, and superposition.

glossary of terms

Background

When two waves meet they create a third wave that is a combination of the other two waves. This third wave is actually the sum of the two waves at the points where they meet. The two original waves are still there and will continue along their paths after passing through each other. After passing the third wave no longer exists.
For more background information
Wave applications to everyday life.
Applet on superposition you will leave this site

Procedure

Part I Superposition of waves

Step 1: Start sending a wave across the screen. From the other side of the screen, send another wave that has the same frequency and phase angle, but has a different amplitude than the fundamental wave. Record your observations.

What happens to the waves when they meet?

Step 2: Using the same fundamental wave, send a wave across the screen. Now, again from the other side, send a wave that has the same frequency and amplitude as the one in step 1 but has a phase angle of 180 degrees to the fundamental wave. Record your observations.

How is this combination of waves different than the one in step 1?

Step 3: Using your orginal fundamental wave add a second wave that differs only in frequency.

Did you get the outcome you expected?

Step 4: Now try different combinations of frequencies, amplitudes and phase angles and see how these waves interfere.

Can you make a wave that is twice as large as the two orginal waves?

Can you produce a wave that has zero amplitude in the middle of the pool?

Problem 1

The Adventures of Marvin the Mouse: You and your friend are walking down by the pool when you hear a cry for help. Poor Marvin the mouse has fallen into the pool and needs your help. The sides of the pool are to slippery for Marvin to climb out but there is an innertube anchored in the center of the pool. Oh no! the sides of the innertube are to slipper and high for Marvin to climb. He's getting tired and can't swim to the sides, he has just enough energy to float by the innertube.

Being physics types and having studyed about waves, (at least a little), you and your friend take up positions on opposite sides of the pool. How did you help Marvin get safely onto the innertube?

Part II Single slit

Step 5: Turn off one of the wave sources. Place a solid object in the path of the wave so that one side of the object touches the top of the pool. Observe what happens to the wave.

Step 6: Place a second object so that it touches the bottom of the pool directly underneath the first object. Make sure there is a large gap between the two objects. Observe the wave.

What happens to the wave as it passes throught the opening?

Step 7: Gradually shrink the size of the opening between the two objects and observe the results. Repeat until the objects touch.

Diffraction refers to the bending of waves around an edge of an object. How close together do the objects need to be before you can see the whole wave bend? Compare this distance to the wavelength of the wave. What do you notice?

Problem 2

Dance Club Designer: You are the designer of a new Dance Club. You have been informed that you need to design the club in such a way that the telephone is placed in a location that allows the customers to hear the people on the other side. The phone company states that they can only put the phone line in at a point 20 meters from the stage.

Develop a model which allows the customers to use the phone with the least amount of trouble given that the phone must be placed at a distance of 20 meters,(2/3 the room size), from the stage. This will be an area where there will be virtually no sound.