Cuesta College, San Luis Obispo, CA
Students have a bi-weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.
The following questions were asked on reading textbook chapters and previewing presentations on double-slit interference.
Selected/edited responses are given below.
Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.
"For in-phase sources, the difference in path length will be a whole number of wavelengths for constructive interference. For destructive interference the path difference will be (a whole number plus) a half of a wavelength."
"The presentation did a good job at conveying the path differences for the double slits. It was defined clearly."
"I understand from this section that the maxima and minima of a double-slit interference means whether or not it is constructive or destructive. this is determined by various variables of a double-slit interference like the wavelength, distance between slits, etc."
"Young's double-slit experiment showed how two monochromatic light sources could interfere constructively and destructively. This was shown by the alternating dark and light fringes on the screen he used."
"The difference in lengths that parallel waves travel is equal to their separation distance d between multiplied by sinθ. The inner wave also travels farther."
"In double-slit interference θ is measured from the horizontal and ranges from –90° to +90° with 0° deg being horizontal. The equation dsinθ is used to find the difference in path lengths traveled by two sets of waves. Whether the resulting wave is constructive or deconstructive depends on the whether there is a whole or and a half difference in path lengths."
Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.
"Maxima and minima were confusing. double-slit interference was more difficult to understand."
"Definitely the picking the correct information to match the equation. All these symbols are confusing."
"The 'Train of Pain' is still a little confusing, just need to a little more with it."
"I understand the equations and the idea of the path lengths pretty well, but I might need some more practice using and applying them."
"I would benefit from homework examples that have to do with calculating the maxima and minima values to acquire a greater understanding of their relationship to the central bright spot."
"I pretty much understood everything, especially the basics. I might need some polishing of some concepts but that's it."
"Nothing at this time."
Explain the difference between "maxima" and "minima" in double-slit interference.
"The resulting constructive interference is the maxima, and the resulting destructive interference is the minima."
"A maxima is where it is brightest and a minima is where it is least bright."
"Maxima refers to the bright fringes while minima refers to the dark fringes."
Match the double-slit parameter with its symbol. (Only correct responses shown.)
Distance between slits: d [74%]
Any positive or negative whole number: m [74%]
Distance from slits to a projection screen: L [49%]
Wavelength of light passing through both slits: λ [83%]
Difference in paths for light passing through both slits: d·sinθ [51%]
Position along screen, as measured from the centerline: y [46%]
Sources: in phase [97%]
Path difference: integer number of wavelengths [100%]
Interference: constructive [97%]
Sources: in phase [89%]
Path difference: odd number of half wavelengths [94%]
Interference: destructive [94%]
Sources: in phase [97%]
Path difference: integer number of wavelengths [77%]
Interference: constructive [74%]
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Would like to review these last two diagrams in or after class."
"Are you going to go over this in class?" (Yes.)
"Will we be doing the double-slit experiment in lab?" (Yes.)
"Since the light that passes through the double slits is from a source that is side-by-side and in-phase with the same wavelength, won't the light passing through the two slits always be in phase?" (Well, yes, unless one wave has to travel a further distance than the other wave in order for them to meet at a receiver.)
"I'm not sure how to use the formula ∆l = dsinθ. In which case will the path difference be a whole wavelength or half a wavelength?" (Well, just calculate ∆l for a given θ direction, then see if it is equal to m·λ or (m + 1/2)·λ.)
"I think that in regards to Young's double-slit experiment, when two light paths interfere constructively they create a bright fringe, and when they interfere destructively they produce a dark fringe... is that correct?" (Yes.)
"I was a little confused whether the double-slit experiment only works when the light sources are side-by-side. If you have two separate sources of light that are constructive but that differ in distance does the double-slit experiment still work?" (Yes, but the sources must have exactly the same wavelength, and be in phase with each other. For visible light the most practical way to do this is to have a laser illuminate two side-by-side slits simultaneously.)
"I would benefit from some practice problems."
"Going to try my hardest to make it tomorrow."
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