Your group is involved in a project investigating some properties of viruses. Yo
ID: 3161196 • Letter: Y
Question
Your group is involved in a project investigating some properties of viruses. You need to categorize viruses by size, but have found that they are too small to view with any microscope that uses visible light. You know, however, that for a small object illuminated by coherent light, a diffraction pattern will be formed rather then an image. The size of an object can be determined from its diffraction pattern, and you would like to try an interference technique with viruses Two issues occur to you. The first issue is, of course, how to determine the size of an object from its diffraction pattern. The second issue has to do with the form in which the viruses will be studied. Your group can isolate a single type of virus, but cannot isolate a single example of the virus. As a result, you will be forced to study the pattern produced by several viruses in very close proximity to one another. You hope that some information about the size of a single virus can be extracted from the pattern formed by many viruses. If the technique is to be useful, you must be able to distinguish the diffraction pattern due to a single virus from the pattern that results from several copies of the same type of virus In this problem and the previous problem, Interference Due To A Double Slit, you study light interference in a simplified system to explore how these two issues can be dealt with. In the present lab problem, you will develop a technique for determining the size of a single object from its diffraction pattern. A diode laser will be the light source and a narrow slit will represent a virus. You are interested in what type of diffraction pattern is formed and how the pattern depends on the width of the slitExplanation / Answer
It is well parallel. Your eye lens will focus all of the beam's power into a small spot on your eye's retina. Before your blink reflex functions, enough energy will be absorbed to temporarily damage the spot. Permanent blindness may result from prolonged exposure to any laser beam, including those from small laser pointers.
Turn on the laser and open the shutter. Let it warm up for a few minutes to achieve a stable beam.
Arrange the laser and the slide with single slits on the optics bench. The laser should be parallel to the optics bench and perpendicular to the slide, and its beam should be aimed at one slit. The screen should be vertical and perpendicular to the optics bench. Adjust the positions so that you clearly observe a diffraction pattern on the screen.
How does the diffraction pattern compare with your predictions? Which features did you predict, and which ones did you not predict?
How does the diffraction pattern change for different slit widths? How does the pattern change when you adjust the distance from the slit to the screen? What happens if you rotate the slit from a vertical to a horizontal position? Do your observations match your predictions?
How does the diffraction pattern of a single slit compare with the diffraction pattern of a pair of slits with the same width? Does this bode well for the virus project? Do you think the laser is important for this problem? Do you have any other sources of light to try instead of laser? What do you see?
MEASUREMENT
Continuing your exploration, sketch the diffraction patterns for two different slit widths.
Fix a sheet of paper on the screen. Mark maxima of diffraction pattern on the screen. (If the maxima are difficult to locate visually, mark some positions so that the central part of each spot can be precisely determined from the marks.) Be sure to record the slit width and the distance from the slit to the screen.
Repeat this operation for at least two different distances and at least two different slit widths.
Remove the slit from the system, and observe the pattern produced when laser light shines on a human hair. Do you see a diffraction pattern? Measure and record the distance from the hair to the screen, as well as the positions of the diffraction maxima.
ANALYSIS
Compare the sketches you prepared during measurement to the graphs from your warm-up questions answers. Do the patterns match?
Use your measurements and the relationships from the prediction to determine the wavelength of the laser light from each trial. Do you obtain a consistent value across different trials? If so, is it comparable to the accepted value for the wavelength of light produced by a Helium Neon laser?
The diffraction pattern due to a solid object (a hair, for example) is the same as that due to a hole of the same shape. Use your measurements to determine the width of your hair.
CONCLUSION
Do the expressions you predicted match the diffraction patterns you observed? If they do not match perfectly, identify some sources of error, and explain how they could result in the observed errors.
Do your observations provide evidence for the wave nature of light?
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.