WAVE INTERFERENCE
Simulation: http://www.surendranath.org/Applets/Waves/TWave02/TW02.html
What happens when two waves meet while they travel through the same medium? What effect will the meeting of the waves have upon the appearance of the medium? Will the two waves bounce off each other upon meeting or will the two waves pass through each other?
Wave Interference occurs when two waves meet while traveling along the same medium. To begin our exploration of wave interference, consider two pulses of the same amplitude traveling in different directions along the same medium.
1 . Predict what will happen in the following situation. The green line is your midline. Sketch your prediction:
2 . Open Simulation 2. Don’t change any settings. Click start. You can advance it slowly by using the cursor. Draw the new wave, represented by the YELLOW line.
Does the behavior shown in the simulation agree with your prediction?
This type of interference is called
.
Constructive Interference occurs when the wave amplitudes reinforce each other, building a wave of even greater amplitude.
3 . What would happen if the pulses are inverted, i.e. a trough meets a trough? Sketch the resultant wave:
4 .
In the slinky lab your group produced constructive interference. What did you do that produced a constructively interfered wave? What observations did you make that support your answer? Talk about when you produced constructive interference.
5 .
Another type of interference occurs when the waves are out of phase i.e. a crest meets a trough. Sketch your prediction below:

6 . Click STOP on the simulation and select EQUAL Amplitude and OUT Phase. Draw the new wave, represented by the
YELLOW line (remember you can :
Does the behavior shown in the simulation agree with your prediction?
This type of interference is called
Destructive Interference occurs when the wave amplitudes oppose each other, resulting in waves of reduced amplitude.
7 .
In your slinky lab, you created destructive interference. What did you do to model destructive interference, and what observations support your answer?
8 . Now suppose that the pulses have different amplitudes. Predict what would happen by drawing a sketch:
9 . Click STOP on the simulation and select UNEQUAL Amplitude. In this simulation the wave with larger amplitude is the red wave. Draw the new wave, represented by the YELLOW line:
Does the behavior shown in the simulation agree with your prediction?
PRINCIPLE OF SUPERPOSITION
To determine the resultant wave we can use the Principle of Superposition :
“When two waves interfere, the resulting displacement of the medium at any location is the algebraic sum of the displacements of the individual waves at that same location ” (you add the amplitudes together).
Remember that above the midline is a positive amplitude, below is negative!

1. To determine the precise shape of the medium at a given instant in time, the principle of superposition must be applied to several locations along the medium.
3 . For each labeled point on the graph, decide if the waves will interfere constructively or destructively. Write the letter in the appropriate category.
ACTIVITY 2 CONCLUSION
1 . Sound is a pressure wave that consists of compressions and rarefactions (It’s a longitundinal wave, but behaves the same as the transverse waves explored). Explain constructive interference of two sound waves in terms of pressure variations. (stuck? Animation at
2 . A friend tells you that the word destructive tends to imply that the energy as well as the form of the waves is destroyed.
Do you agree with your friend? Explain your answer, citing evidence from the simulations today.

Activity 3: Standing waves
1. Click on the simulation and select CONTINUOUS, UNEQUAL Amplitude and OUT Phase. Pay attention to the yellow line that results. Draw what you see. DO NOT PAUSE THIS SIMULATION!
What kind of wave is the yellow wave?
2 . Click on the simulation and select CONTINUOUS, EQUAL Amplitude and OUT Phase. Pay attention to the yellow line that results. Draw what you see. DO NOT PAUSE THIS SIMULATION!
What kind of wave is the resulting yellow wave?
2 . Click on the simulation and select CONTINUOUS, EQUAL Amplitude and IN Phase. Pay attention to the yellow line that results. Draw what you see. DO NOT PAUSE THIS SIMULATION!
What kind of wave is the resulting yellow wave?
ACTIVITY 3 CONCLUSION
1 . What is required for a standing wave (a wave that appears to stay in one place) to form?
2 . What is the relationship between the nodes and anti-nodes of a standing wave compared to the intersections and interactions of the two original waves? (go back to your simulation of a standing wave, and pause it at various times until you see a pattern)
Nodes are formed where ____________________________________________________________________
Anti-nodes are formed where ___________________________________________________________________
3. What would you do in order to make a standing wave with a slinky?