Waves Simulationdate

Physics 513Name

Waves SimulationDate

Waves Websites

Answer all of the questions right in this packet. Rather than typing in all of the URLs, all of the links are posted on my Teacher page on Schoolwires. For all of these applets, they have you manipulating the wavelength. We know that this is really done by manipulating the source (frequency) or the medium (speed) of the wave but these demos blur that distinction.

Part 1 – Reflection from a Concave Barrier

This link will take you to a YouTube video of an old black and white film strip. I grant that the quality is not great.

From 0:00 to 0:45, the video shows the reflection of a circular wave made by a point source off of a concave, parabolic boundary. What is the most important lesson from this section of the video?

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From 0:45 to 1:33, the video shows the reflection of a circular wave made by a point source off of a concave, CIRCULAR boundary. How are these reflections similar to AND different from those off of a parabolic boundary?

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Also during this section, they superimpose a parabola over the semicircle. What point is the video trying to make?

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Part 2: The Superposition of two sinusoidal waves

Set the two waves so that they have an equal wavelength and equal amplitude and a phase of 0. Describe the “sum” wave” compared to the component waves

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Change the phase of wave 2 to 180o. Describe what happens and why it happens (look at the two component waves in relation to each other to explain)

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Change the phase of wave 2 back to 0o. Change the wavelength of wave 2 to 20. Draw a quick sketch of the pattern, describe what you see in words and write a brief description of WHY this is the resulting pattern.

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Sketch:

Change the wavelength of wave 1 so it is 17 and wave 2 so it is 15. Describe what you see. Draw a sketch and describe what you see. (By the way, this pattern is known as a beat frequency which we will discuss later)

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Sketch:

Part 3 – Standing waves.

Turn the ruler on and move the amplitude slider all the way to the right.

Initially, how far is the source from the boundary? ______

When the source frequency is 25 Hz, you should see an n= 1 standing wave occurring.

How many nodes are there? ______How many antinodes? ______

What is the wavelength of this wave? ______

Calculate what the speed of the wave on this string must be

Increase the source frequency until you find the n = 2 standing wave pattern.

At what frequency does this occur? ______

How many nodes are there? ______How many antinodes? ______

What is the wavelength of this wave? ______

Increase the source frequency until you find the n = 3 standing wave pattern.

At what frequency does this occur? ______

How many nodes are there? ______How many antinodes? ______

What is the wavelength of this wave? ______

Name two other frequencies for which you would expect standing wave patterns to form

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Pick ANY frequency that you did not look at above. Record here ______

Click and hold on the ring stand and slide it to the left to find a location that gives a standing

wave. At what length does the pattern occur? ______This is a n = ______standing wave.

What is the wavelength? ______Sketch the pattern below:

Part 4 – Diffraction

In this demo, you will be looking for the DEGREE OF CURVATURE of the diffracted waves. A high degree of curvature means the central grouping of waves looks closer to a semi-circle than a straight line and a low degree of curvature means it looks closer to a straight line than a semi-circle.

Look at the demo for several different wavelengths. As you increase the wavelength, what is occurring to the curvature of the diffracted waves?

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Set the wavelength back to a middling value. Test different slit widths. What occurs to the degree of curvature of the diffracted waves as the width of the slit is decreased.

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Part 5 – Interference of water waves/2-D interference

Click on the “Same applet, larger version” link

In this demo, where you see the blurry, grayish lines, waves are being canceled out. The lines along where destructive interference occurs are called NODAL LINES. Where you see clear crests (white lines) and troughs (dark lines), that’s where waves are constructively interfering. These lines are called ANTI-NODAL LINES.

How would you describe the pattern in words?

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Increase the wavelength. As you increase the wavelength, what happens to

the distance between each adjacent nodal line? ______

The width of each antinodal line? ______

Return the wavelength to the original value. Decrease the source separation. What happens to

the distance between each adjacent nodal line? ______

The width of each antinodal line? ______

If you click on any point in the simulation, it will show waves leaving each of the two sources and meeting at that point. It shows what each wave is doing at that point by looking at the vibration of the two blue dots at that point.

Click at several locations on different anti-nodal lines. Try to click in the middle of these lines.

Are the waves in phase or out of phase when they meet? How do you know?

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Why does this make sense based on what you know is happening at an anti-nodal line?

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Click at several locations on different nodal lines. Try to click in the middle of these lines.

Are the waves in phase or out of phase when they meet? How do you know?

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Part 6 – Refraction

When the simulation starts, you will see a series of wavefronts in the “white” material moving into the “gray” material. What’s relevant to know is that the wave moves SLOWER in the gray material. Also, there is no normal line drawn so you will have to imagine it.

Based on our discussion, what about the picture lets you know the waves were slowing down as they entered the gray medium?

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On the simulation on the right, you will see the angle of incidence listed (initially it is 30o). A few boxes below this, you will see the angle of refraction.

With an angle of incidence of 30o, what is the angle of refraction? ______

Increase the angle of incidence by 5o a few times. As you do this, each time the angle of refraction (circle the correct answer)

Increases but by more than 5o each timeDecreases but by more than 5o each time

Increases by 5o each timeDecreases by 5o each time

Increases but by less than 5o each timeDecreases but by less than 5o each time