Wave Effects lab

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Hartnell College *

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Physics

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Jan 9, 2024

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Physics Experiment: Light as a Wave Name: Breana Aguilar Date: 11/5/23 Part 1: Diffraction 1) Go to: https://phet.colorado.edu/en/simulations/wave-interference 2) Roll over “SIMULATIONS and click on “Physics” 3) Scroll down to “Waves Interference” and click on it. 4) Click on: 5) Click on: 6) Get familiar with all the controls, make changes, interact with the simulation. 7) Now that you are familiar with the simulation, select the box ; adjust the width and height so you get a tall, narrow opening 8) Select a wavelength near one end of the color spectrum – you choose and then turn on the light 9) Describe the diffraction pattern that appears: a The diffraction patterns show long, thin lines on both ends of the central point. The center point is a bolder line and the color begins to fade and the lines appear shorter as they get further. 10) How is the diffraction pattern oriented, relative to the opening? a The diffraction pattern is oriented inversely to the opening which is horizontal versus the initial opening which is vertical. 11) Now make the opening short and wide. 12) Describe the diffraction pattern that appears: a The diffraction pattern appears similar to that of the previous, however this diffraction is vertical. 13) How is the diffraction pattern oriented, relative to the opening? a The diffraction pattern is oriented inversely relative to the opening. 14) Now max out the width and height of the opening 15) Describe the diffraction pattern that appears:

a The diffraction of the pattern appears to look like a starlight, it is a much longer and thinner, cross. The center appears smaller than the previous and there are far more rectangles dimming from each end of the center square. 16) How is the diffraction pattern oriented, relative to the opening? a The diffraction pattern is oriented inversely, again, since the square from the opening is large and the patter is small. 17) Now minimize the width and height of the opening. 18) Describe the diffraction pattern that appears: a The diffraction pattern appears to be in a cross of dimming, thinner rectangles, the center is more of a brighter square shape. 19) How is the diffraction pattern oriented, relative to the opening? a The diffraction pattern is oriented inversely in that it has a larger image than that of the original opening. 20) Now, change the wavelength to the other side of the spectrum. For example, if you chose the red end of the spectrum for the previous steps, move the wavelength slider to the blue end of the spectrum. 21) Describe the diffraction pattern that appears: a The diffraction pattern is different as the original wavelength was on the blue end and now by moving it to the red end, the pattern is more vibrant and bolder than the blue. The squares even appear larger. 22) How is the diffraction pattern oriented, relative to the opening? a The diffraction pattern is the same as it previously was, inversed. 23) How does this diffraction pattern compare to the diffraction pattern of the previous color? a The diffraction pattern is larger and more defined in shape. 24) Now max out the width and height of the opening 25) Describe the diffraction pattern that appears: a A larger cross that has a strong square in the center and a dimming of red rectangles out of each side. 26) How is the diffraction pattern oriented, relative to the opening? a The opening is large and the patter is very small. 27) How does this diffraction pattern compare to the diffraction pattern of the previous color? a Its similar but longer of a strand of rectangles. 28) Now make the opening short and wide. 29) Describe the diffraction pattern that appears:

a The pattern is a lot larger than the purple end showed. The rectangle is longer and more vibrant. 30) How is the diffraction pattern oriented, relative to the opening? a The opening, is inversely oriented as it is horizontal but the patter vertical. 31) How does this diffraction pattern compare to the diffraction pattern of the previous color? a The pattern is thicker and more noticeable. 32) Now make the opening tall and narrow. 33) Describe the diffraction pattern that appears: a The pattern is bigger and there are less rectangles compared to the purple. 34) How is the diffraction pattern oriented, relative to the opening? a The pattern is inverse and horizontal as the opening is upright. 35) How does this diffraction pattern compare to the diffraction pattern of the previous color? a It is wider and brighter with a stronger appearance of thinner dimmed rectangles going upright. 36) Explain how this shows light behaves like a wave. a The higher the frequency of a wave, the more light that it will let in. 37) Get a screenshot or picture of your setup.

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Part 2: Interference 2) Select light 3) Set Amplitude in the middle 4) Turn on: a. Screen b. Intensity 5) Pick a color with the frequency slider and write the color you chose. 6) Turn on only one of the lights . 7) Describe how you can determine the wavelength of the color of light you chose using any or all of the tools and controls in the simulation. a You can use the stopwatch tool to track how long it takes for an amount of waves to form. To calculate the wavelength you can divide the amount of waves by the time it took. b 5 waves / 2.91 sec = frequency = 1.72 Hz c measured 2356.2nm / 1,000,000 = 0.0023662m 8) Now go figure out the wavelength of the light you chose and write it here 0.0023662m ________. Be sure and put correct units on it! 9) Calculate the frequency of the color of light you chose (you may need to check your notes or the textbook to find an equation to use). Write the frequency of the color you chose, here here 1.718 Hz Be sure and put correct units on it! 10) If you changed the Amplitude, set it back to the middle and describe the intensity chart. a The intensity it low and not moving as fast. 11) Now, max out the Amplitude. How did the intensity chart change? a The intensity of the waves are stronger and they are even bolder. 12) Pick a new color with the Frequency slider. After letting the waves propagate across, describe how the intensity chart compares to the previous color. a By switching the frequency to red, the intensity is moving much more and stronger than the blue. 13) Turn on the other light and let the waves propagate across. Describe the intensity chart; how many “bumps” appear and how tall are they compared to the previous intensity chart? a There are two bumps with a maxed out amplitude and the red frequency this is definitely stronger and they are taller than the previous.

14) Change the Amplitude back to the middle. Describe the intensity chart; how many “bumps” appear and how tall are they compared to the previous intensity chart? a There are three bumps now but they are shorter and less intense than the previous. 15) Now, max out the separation (4000 nm) and let the waves propagate across. Describe the screen at the right side of the simulation (next to the intensity chart) and the intensity chart. a There are 5 waves now and they are closer together. The screen does not look at all as it previously did it looks more like a checkerboard. 16) Vary the Amplitude; describe what affect it has on the screen and the intensity chart. a The higher than amplitude, the more bumps are present in the intensity chart. 17) Vary Frequency; describe what affect it has on the screen and the intensity chart. a The higher the frequency, the more bumps but they are shorter and closer together. 18) What settings can you change in the simulation to change the number of colored lines on the screen? a Frequency, amplitude ,and separation 19) Adjust the settings on the simulation to get the brightest and most lines on the screen. List your settings, here: a Max out frequency, amplitude, and separation. 20) What causes the alternating dark and colored areas on the screen at the right side of the simulation (next to the intensity chart)? a What causes the alternating dark and colored areas on the screen at the right, is that the waves from the lights combine to hit the screen in different areas. 21) Explain how this demonstrates light behaves like a wave. a This shows that the two lights are extractive waves, and they come together to combine and make the lines 22) Get a screenshot or picture of your setup. 23)

Part 3: Slits 1) 2) Select light 3) Turn on: a. Screen b. Intensity 4) Based on your experience in parts one and two of this lab, describe what you expect to happen to the light pattern as you vary the number of slits, the width of the slits, and the separation between the slits. a As the slit gets bigger, the waves will get smaller and vice versa. 5) Pick a color to use. What color did you choose? a Red 6) Set Amplitude to maximum. 7) Turn on the light generator. 8) Determine the wavelength and frequency of the color you chose. λ = 0.0029779m (don’t forget to put correct units on your answer) f = 0.731 Hz (don’t forget to put correct units on your answer) 9) Set the simulation for 1 slit with a width of 200 nm. Describe what appears on the screen and the intensity chart. a The screen looks standard and the intensity chart is low with a slight bump. 10) What do you expect to happen if you lower the Amplitude? a The screen dims down and the intensity drops and is not noticeable on the chart. 11) Set Amplitude in the middle. Did it do what you expected it to? a Yes, the screen is in between in vibrance and the intensity is barely moving. 12) DON’T MOVE ANYTHING YET! Notice near the bottom of the simulation the double green Down at the bottom, select

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arrows . Those will move the position of the slit to the left or right. BEFORE MOVING THE SLIT, what do you think will happen to the screen and intensity chart if you move the slit to the left (closer to the light source)? What do you think will happen to the screen and intensity chart if you move the slit to the right (farther from the light source)? 13) Move the slit closer to the light source and describe what you see on the screen and intensity chart. a There is very little activity on the right side and the intensity. 14) Move the slit farther from the light source and describe what you see on the screen and intensity chart. a There is a good amount of intensity 15) What changed on the screen and intensity chart when you moved the position of the slit? a It raised due to the intensity the further away it was. 16) Put the slit back half-way between the light and the screen. 17) Set the simulation for 2 slits, 200 nm slit width, and slit separation of 1600 nm. 18) Describe what you see on screen and intensity chart. a There is a slight intensity showing three small bumps and not such strong waves. 19) Change the slit width to 400 nm. Describe what you see on screen and intensity chart. a There are three bumps on the intensity chart and the waves have spread into three. 20) Change the slit width to 800 nm. Describe what you see on screen and intensity chart. a The intensity increased and there are three bumps however the center bump is the largest. 21) What changed on the screen and intensity chart as you increased the slit width? a The higher the slit width the higher the intensity and more waves are seen. 22) Change the slit separation to 2400 nm. Describe what you see on screen and intensity chart. a If it is separated to that, the intensity starts decreasing. 23) Change the slit separation to 3200 nm. Describe what you see on screen and intensity chart. a The intensity fluctuates but ultimately gets smaller as the slit separation increases. DON’T MOVE ANYTHING YET!

24) Using the double green arrows, ,move the slit closer to the light source and describe what you see on the screen and intensity chart. 25) Now, move the slit farther from the light source and describe what you see on the screen and intensity chart. a When moved further away from the light, the intensity starts going away because of the distance. 26) What changed on the screen and intensity chart when you moved the position of the slit? a Moving the position of the slit is the number one factor of the intensity chart being altered. 27) Adjust the settings on the simulation to get the brightest and most lines on the screen. List your settings, here: a Put the slit as far away from the light as possible and high separation so the intensity increases. 28) Get a screenshot or picture of your setup. Part 4: Summary Explain, in complete sentences, how Young’s Double Slit experiment (diffraction, wave interference, etc.) demonstrates light behaves as a wave. Young's Double Slit experiment is a classic demonstration of light behaving as a wave. This experiment supports the wave nature of light. In the setup of the experiment, a coherent light source, such as a laser, is directed towards a barrier with two narrow slits. These slits act as sources of secondary ripples of waves. As the light passes through the slits, it diffracts, which means it spreads out and forms a pattern of alternating bright and dark rays

on a screen placed behind the slits. The diffraction of light occurs because each slit acts as a point source, and the waves from these sources interfere with each other. This interference creates areas of constructive and destructive interference, resulting in the observed pattern. The bright rays correspond to constructive interference, where the peaks of the waves from the two slits overlap, reinforcing each other and producing a bright spot. The dark rays correspond to destructive interference, where the peaks of one wave overlap with the gaps of the other wave, canceling each other out and resulting in a dark spot. The spacing between the rays are directly related to the wavelength of the light. By measuring the distance between the rays and knowing the distance between the slits, one can determine the wavelength of the light. This experiment demonstrates that light behaves as a wave because the observed interference pattern is a characteristic feature of wave phenomena. It shows that light waves can diffract and interfere with each other, indicating wave-like behavior. The ability of light waves to interfere and create a pattern supports the wave nature of light.

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