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lab 4

1) n the simulation, you can see a top view, side view, and graph of this scenario. Use the simulation to create a pattern similar to the one at the right. Describe what is happening in the simulation to create this pattern.link see below https://phet.colorado.edu/sims/html/wave-interference/latest/wave- interference_en.html ) Challenge Question: Obtain a pan and fill the pan with water. Try to produce the pattern and describe the method you used for producing the pattern. note: The part with the pan is a challenge question. Any credit earned here is extra credit and you may skip the pan experiment without penalty. 2) The diagram shows the locations of the wavefronts at one instant in time, as a photograph would. How, if at all, would the diagram differ: one-quarter period later? Explain. one period later? Explain. Be sure to describe both cases and remember that the period is the time from one wave crest to the next wave crest. 3. Using the simulation, try to produce the pattern above again but this time create a pattern with a smaller wavelength. How did you do it? What did you change in the simulation to shorten the wavelength? How would you produce a pattern with a larger wavelength? Challenge question: Try to produce the pattern with a shorter wavelength in your pan of water. How did you do it? 4.) Using the simulation, try to produce the pattern above again but this time create a pattern with a smaller wavelength. How did you do it? What did you change in the simulation to shorten the wavelength? How would you produce a pattern with a larger wavelength? Challenge question: Try to produce the pattern with a shorter wavelength in your pan of water. How did you do it?

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5) Periodic circular waves: two sources


The diagram at the right illustrates the wavefronts due to each of two small sources. Click on the “Interference” tab of the simulation found at the bottom of the window and produce this pattern with water. Explain how you did it. Challenge Question: Try to produce this pattern in your pan of water. Explain how it worked with an actual pan of water.   7)   Each of the photographs shows a part of a ripple tank that contains two sources that are in phase. The nodes are those places in the pattern where the surface of the water is at equilibrium level, neither peaks nor troughs. For each of the photographs, identify the lines of nodes.

How many nodal lines are there in the picture at left? (Ignore the horizontal ones for now.) Answer

How many nodal lines are there in the picture at left? (Ignore the horizontal ones for now.) Answer 8)what difference(s) in the two situations could account for the difference in the number and the locations of the lines of nodes? Play with the simulation to try to reproduce each picture. Describe what worked to increase the number of lines of nodes. 9) In the simulation there are buttons to switch between water waves, sound waves and light waves. The buttons are in the upper right menu box under the slider that adjusts separation. View the simulation for sound waves and light waves. How do the patterns for water waves, sound waves, and light waves compare?

12) Observe: Use the water-level indicator graph in the simulation to test your predictions. The water level indicator is in the row of tools in the top right, the one furthest to the right. Set up the two probes at two crests in the paused simulation and then start the simulation and watch what happens to the water level at the two points.   13) Pause the simulation and move the probes to two nodes. You can tell when you are exactly at the node because the dot on the graph will be at the center of the chart.

Restart the simulation. Describe what happens to the height of the water at the point of the two nodes over time. 13) 14) Suppose that a small leaf or bug were floating on the surface of a pond. Use your diagram to predict where it would move

1. the least and 2. the most.

Enter your predictions in the text box below.  

Interference: Summary Answer the following questions and submit your responses as a PDF. 1. Write down one major conclusion you can draw from this week’s laboratory. Please explain. 2. Describe the experimental evidence that supports your conclusion. Please explain. 3. Give one example of applications/situations for the finding(s) you described above in your everyday life outside of physics lab.

4. What did you like and dislike about this week’s lab?  

Interference Lab Post-Lab Knowledge Check PHYS 242

1. Above is a diagram of the wavefronts due to two sources. What is the source separation in your diagram? Not everyone’s printout or screen image will be the same size so express your answer in terms of the wavelength. For instance, the two sources might be 1, 2, or 3 wavelengths apart. If the separation is not a whole number of wavelengths enter a decimal number, for instance 2.5 instead of 2 1/2.

2. Using different symbols (or different colors), mark the places at which for the instant shown:

• the displacement of the water surface is zero (i.e., at its equilibrium level) • the displacement of the water surface is the greatest above equilibrium • the displacement of the water surface is the greatest below equilibrium • On your diagram, mark the nodal lines and the lines of constructive interference.

Hint: Look for patterns that will help you identify all of these points.

Interference

Chapter 28: Walker

1

2

The Wave Nature of Light

•  Effects due to the wave nature of light: o  Interference o  Diffraction

•  Examples: o  Ripples on a pond o  Acoustic design o  Reading CDs/DVDs o  Pretty colors on soap bubbles o  Irridescent butterflies o  Etc.

3

Water Waves

•  Try at home: put water in a shallow pan o  Tap with two fingers o  Make waves and slits with blocks of wood

4

Interference

•  Constructive and destructive interference and the principle of superposition o  Constructive: waves add o  Destructive: waves cancel

•  Examples of coherent waves: o  2 fingers tapping on water in unison (water) o  Water waves through 2 narrow slits (water) o  2 loudspeakers driven by same amp (sound) o  Shining laser through 2 narrow slits (light) o  Easier to observe in everyday life for water than for

light because of size of wavelength

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Begin with Water Waves Consider circular waves in a tank:

______________ = the distance from crest to crest (or trough to trough) ________ = the distance from crest to trough

crest

trough

Look along the dotted line.

What is the shape of the water on the dotted line?

crest trough crest

trough

x

crest

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(1/2 λ) Wavelength (1 λ)

x

x

crest

trough

y

height of water above equilibrium

level

Equilibrium level

λ

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Again, •  (1 λ) = the distance from crest to crest

(or trough to trough) •  (1/2 λ) = the distance from crest to trough

x

y

Crest and crest Crest and trough

Now think about the water level when wavefronts interfere

8

x

y

x

Wave 1

Wave 2

+

x

superposition

y2 y1

y1+y2

y1 y2

y1+y2

Total Constructive Interference 9

x

Wave 2

x

y Wave 1

superposition

y2

y1

y1+y2 = 0

+

Total Destructive Interference

Shifted λ/2

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Animation: Sources in phase

Increasing source separation

•  _____ when crest meets crest (constructive interference) •  _____ when trough meets trough (constructive) •  _____ (_____) when crest meets trough à line of nodes (destructive interference)

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High Low Zero flat

Lab: Interference

•  What patterns do you notice?

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