Physics quiz archive: interference, electrostatics

Physics 205B Quiz 3, spring semester 2020
Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz03Cv1d



Sections 30882, 30883 results

0- 6 :
7-12 :
13-18 :	**** [low = 15]
19-24 :	***************
25-30 :	*************** [mean = 24.2 +/- 4.2] [high = 30]

Online reading assignment: diffraction

Physics 205B, spring semester 2020
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 diffraction.


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.

"I understand that when you decrease the size of W, then the theta or spread increases, and visa versa, increasing W would lead to a more narrow spread, which helps with telescopes. I also understand how waves can bend around the edges of the slit, not just shining directly through."

"Diffraction is the bending of light waves around obstacles or edges of an opening. As light moves through a slit, it will result in an angle that will vary depending on the size of the opening. As the W (width) of the slit increases in size, the angle of light expelled decreases. As W decreases, the angle will increase."

"Diffraction is the bending of waves around obstacles. I also understand that the degree of bending in light is much less than in sound."

"The diffraction minima is given by W·sinθ = m·λ where W is the width of a single slit, θ is the angle of the spread from the center, and λ is wavelength of light."

"Diffraction is how light is perceived and bends through a slit. What is important is how large the wave length is and what the angle it is exiting from the slit at compared to the 'normal.' As the slit increase, the minima angle decreases and vice versa. When talking about telescopes, they use a large width so the angle must be small to resolve details of far-away objects."

"Essentially, decreasing slit width W causes an increase in the 'spread' of the half-angle θ. Conversely, increasing slit width would produce the opposite effect onto the spread of θ."

"The slit width and analogies were perfect. The example in the ocean with the waves is both a pun and a great example! "

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.

"The dark fringes for single-slit diffraction was confusing to me."

"I guess I didn't really understand what a slit is."

"I am confused about how to find the minima angle. I am also unsure of where it comes in and if it is only with destructive interference."

"I was confused about the midpoint of a central bright fringe. I did not understand what that had to do with the destructive interference. "

"What is the difference between spread angle and diffraction minima?"

"I am slightly confused as to what effects the relationship of slit width and spread of theta cause. Looking at the telescope example, I believe I understand the idea that a larger slit with produces a smaller theta causing less spread and a more refined image."

"I'm not understanding the diffraction of light through the telescope, and the hair laser example."

"Not much really. A few examples and minor explanation should get me up to speed."

"I didn't find anything confusing about this topic. "

"Honestly just haven't got to this yet."

Match the single slit parameter with its symbol. (Only correct responses shown.)

Width of a single slit: W [94%]
Wavelength of light passing through the slit: λ [97%]
Direction, as measured from the centerline: θ [97%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"May you explain the textbook diagrams in class? The textbook's diagrams and graphs made the concept more difficult."

"Light without diffraction would pass straight through a narrow slit without spreading out?"

"By making the slit width larger and larger does there reach a point where making the slit larger would result in an inconsequential reduction in the spread of the diffracted waves?" (Yes. If the slit were large, then diffraction (the "wrapping around the edge effect") would be less noticeable, and the light would not seem to spread out much, so the beam would have the same size/shape as the slit. If the slit were very small, then the "edge effect" would be more noticeable, and the light will spread out more such that the beam would "fan out.")

"What is the m referring to in the equation sinθ=m·λ/W), as explained by the textbook? Will there ever be a time when m will be more than 1?" (Yes, in order to find the fainter dark fringes off to the side of the "spread angle" (where m = 1), but we'll only concentrate on the light contained within the m = 1 "spread angle," because that's where most of the spread-out light is concentrated after passing through the slit.)

"I was curious as to what happens when two slits are close to each other. Can they have constructive interference?" (Yes, provide that each slit is small enough that light will spread out (diffract) so they will overlap with each other, and then can interfere with each other.)

"I am glad you're my professor. My other class I felt so lost the whole time but this semester I don't."

Physics quiz archive: interference, electrostatics

Physics 205B Quiz 3, spring semester 2019
Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz03b3Am



Sections 30882, 30883 results

0- 6 :	** [low = 3]
7-12 :	**
13-18 :	*********
19-24 :	***************** [mean = 21.5 +/- 6.0]
25-30 :	************ [high = 30]

Online reading assignment: diffraction

Physics 205B, spring semester 2019
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 diffraction.


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.

"Diffraction is the bending of waves around obstacles or the edges of an opening. Huygens' principle states every point on a wave front acts as a source of tiny wavelets that move forward with the same speed as the wave; the wave front at a later instant is the surface that is tangent to the wavelets. Dark fringes for single slit diffraction sinθ = m⋅((wavelength λ)/(width of slit W)) where m = 1, 2, 3, ..."

"Through a smaller diameter aperture, light detracts and spreads more, resulting in a less resolved image. A larger diameter aperture, light diffracts and spreads less, resulting in a more defined image."

"Light passing through one slit will have diffraction in which the waves spread out past the slit. The wider the slit, the smaller angle of diffraction, and the smaller the slit, the bigger angle. Single-slit wave diffraction can be demonstrated using three variables: the slit width (W), the spread angle (θ), and the wavelength (%lambda;). The diffraction minima equation relates the width and the spread angle to the wavelength, accounting for the initial hose example."

"I understand the concept that if the width, W, is wider, the half-angle will be smaller, and if the W is smaller, then the half-angle will be wider. The analogy of the graden hose is very helpful."

That the single slit width W has an inverse relationship with the spread angle. As width increases, spread angle decreases, and vice versa."

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.

"I understood why a smaller value for width caused more diffraction because width is in the denominator, however I don't quite understand how the light bends around objects like a slit."

"This reading didn't present much I didn't understand. The concept seems relatively straightforward."

"I was just a little confused about the equations mentioned and how to use them and what they're used for."

"Why would the θ of diffraction get bigger as W gets smaller?"

"What I don't understand is why the spread angle gets smaller when the width gets larger. It seems to me like it would be the other way around."

"I got a bit lost in the how increasing/decreasing the width making the spread angle decrease/increase. It just seems sort of backwards to what I thought it would be."

"I don't understand the difference between angle spread and diffraction minima."

"The equations and diagrams seemed a bit confusing. Examples and equation walkthroughs in class would be helpful."

"I didn't understand the difference between the central bright fringe and the dark fringes. I also need to better understand how to find the central bright fringe (the dark fringe is the formula presented in the book and online lecture)."

Match the single slit parameter with its symbol. (Only correct responses shown.)

Width of a single slit: W [90%]
Wavelength of light passing through the slit: λ [90%]
Direction, as measured from the centerline: θ [90%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"I enjoyed this reading."

"Excited to do excellently on the quiz tomorrow!"

"I found Huygens' principle confusing with its terminology of wavelets. What is a wavelet and how does it pertain to diffraction?" (In class we'll apply Huygen's principle and wavelets to explain how diffraction is analogous to how waves "wrap around corners.")

"I was kind of confused at the end of the presentation when the lab was briefly explained and states that shining a laser at a single hair is like waves traveling through a single slit... I guess I would need more explanation to figure out how that is exactly." (We'll discuss in class how waves will "wrap around" each edge of an opening and spread out, but also waves can "wrap around" each edge of an obstacle, and then cross over each other as they spread out.)

"More of a general math question: what is the physical significance of using the sine of an angle and, specifically, how is it applied for single-slit wave diffraction?" (We'll see how that sine appears when we discuss double-slit interference in much more detail in lab and in lecture.)

"Is this class going to talk about the dark matter?" (No, but we do get to talk about dark matter in my other Astronomy 210 lecture.)

Physics quiz archive: interference, electrostatics

Physics 205B Quiz 3, spring semester 2018
Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz03Ch4R



Sections 30882, 30883 results

0- 6 :
7-12 :	** [low = 9]
13-18 :	****
19-24 :	************ [mean = 23.3 +/- 4.9]
25-30 :	************** [high = 30]

Physics quiz question: moving screen away from single slit

Physics 205B Quiz 3, spring semester 2012
Cuesta College, San Luis Obispo, CA

Light from a red laser illuminates single slit to form a diffraction pattern on a distant screen. If the distance from the slit to the screen is increased, the width of the central maximum on the screen would:
(A) increase.
(B) remain the same.
(C) decrease.
(D) (Not enough information is given.)

Correct answer (highlight to unhide): (A)

From the first minima equation (which uses the angle that measures one-half of the width of the central maximum on the screen), where W is the width of the slit:

W·sinθ = (1)·λ,

such that the "spread angle" is given by:

θ = sin^–1(λ/W).

Since the wavelength λ and the slit width W remain constant, the "spread angle" θ is unchanged if the distance from the slit to the screen in increased.

However, from trigonometry, the relation between the angle θ and the adjacent leg L (distance from the single slit to the screen) and the opposite leg y (one-half of the width of the central maximum on the screen) is given by:

tanθ = y/L,

where:

θ = tan^–1(y/L),

and since the distance L from the slit to the screen is increased, while the "spread angle" θ remains constant (as λ and W are constant), then y, which is one-half of the width of the central maximum on the screen must increase, and correspondingly the width of the entire central maximum on the screen would increase as well.

Section 30822
Exam code: quiz03gR7L
(A) : 21 students
(B) : 3 students
(C) : 3 students
(D) : 0 students

Success level: 78%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.71

Physics quiz question: diffraction through single slits of different widths

Physics 205B Quiz 3, spring semester 2014
Cuesta College, San Luis Obispo, CA

Light from a green laser pointer (wavelength 532 nm) illuminates a single slit. If the slit is made narrower than __________, the first diffraction minima will not be visible anywhere on a screen.
(A) 266 nm.
(B) 532 nm.
(C) 797 nm.
(D) 1,064 nm.

Correct answer (highlight to unhide): (B)

From the first minima equation (which uses the angle that measures one-half of the width of the central maximum on the screen), where W is the width of the slit:

W·sinθ = (1)·λ,

such that the "spread angle" is given by:

θ = sin^–1(λ/W).

Since both responses (C) and (D) have slit openings greater than 532 nm, they will produce a first minimum fringe at θ = 41.9° and 30°, respectively.

Response (B) has a slit opening that is equal to the 532 nm wavelength, such that θ = 90°, which is the boundary case where an opening slightly larger than 532 nm that would result in a spread angle slightly less than 90° (and thus be visible on a screen), and an opening slightly smaller than 532 nm would result in an undefined spread angle, as the inverse sine function would operate on a value greater than 1, so there would be no first minimum fringe at any angle (or on a screen) if the slit opening W is less than 532 nm.

Response (A) is already too narrow to produce a first diffraction minima, as it is already smaller than 532 nm.

Sections 30822, 30883
Exam code: quiz03cDvD
(A) : 11 students
(B) : 28 students
(C) : 0 students
(D) : 1 student

Success level: 70%
Discrimination index (Aubrecht & Aubrecht, 1983): –0.05

Physics quiz question: laser diffraction of hair strands

Physics 205B Quiz 3, spring semester 2016
Cuesta College, San Luis Obispo, CA

A Physics 205B student uses a red laser (wavelength 632 nm) to separately illuminate two different strands of hair. The __________ strand of hair will produce a wider central diffraction maximum.
(A) thinner.
(B) thicker.
(C) (There is a tie.)
(D) (Not enough information is given.)

Correct answer (highlight to unhide): (A)

From the first minima equation (which uses the angle that measures one-half of the width of the central maximum on the screen), where W is the width of the obstacle (strand of hair):

W·sinθ = (1)·λ,

such that the "spread angle" is given by:

θ = sin^–1(λ/W),

so for a given wavelength of 632 nm, the thinner hair strand (smaller width W) would result in a larger "spread angle" θ.

Sections 30822, 30883
Exam code: quiz03Ccf7
(A) : 29 students
(B) : 11 students
(C) : 0 students
(D) : 0 students

Success level: 73%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.50

Online reading assignment: diffraction

Physics 205B, spring semester 2018
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 presentation on diffraction.


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.

"Diffraction is the spread of light from a single slit. A smaller W (slit width) results in a larger spread angle. This spread angle is the destructive region which is the boundary of most of the diffracted wave energy."

"I understand the idea behind waves spreading after traveling through a single slit. The smaller the slit, the larger the half angle of the spread will be. Also the formula is based on the half angle."

"I understand that when the width of a slit gets smaller the 'spread' increases. And when the width of a slit gets bigger the 'spread' decreases."

"Smaller width means more spread."

"Honestly all I understood was the terminology."

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.

"Most of the presentation seemed fairly clear and to the point. I could possibly use some more clarifications on what exactly the minima angle represents and the difference between the half-angle and the minima angle."

"When reading from the book I didn't really quite get the difference between the central bright fringe and the dark fringes. I don't really understand how to find the central bright fringe whereas the dark fringe is just the formula presented in the book and online lecture."

"What the relationship between the first minima and spread angle?"

"Although I understood the relationship between W and θ, I dont know how to actually calculate that. I am sure we will go over this later."

"The laser hair screen slide was the only part of this lecture slide that was confusing, I just would need to see another example and I will probably be ok."

Match the single slit parameter with its symbol. (Only correct responses shown.)

Width of a single slit: W [97%]
Wavelength of light passing through the slit: λ [97%]
Direction, as measured from the centerline: θ [97%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"I'm scared of how easy this lesson was." (Hmmm.)

"Would these calculations help when deciding where to put a harbor?" (Or designing a sound system. Or a telescope. Or anything to do with minimizing (or maximizing) the spread of water, sound, light, or any other types of waves.)

"Why do we reference a half-angle instead of the angle showed? How does squinting play a part in how well we can see?"

"Lab reports due Monday?" (Yes. Like every Monday now, for the rest of the semester.)

"To get the bonus turn-in credit for the lab reports, we have until the end of the first 10 minutes of class on next Monday? Or should we give it to you this Wednesday? (Either is fine.)

"I miss the old classroom." (I do, too; but Physics 205B usually gets put into 2401 instead of 2402, and you do not want to be in 2401 (the biology forum).)

"I honestly just raced through this because I'm in Utah trying to shovel snow, put chains on and make it back into town." (Let's see if you made it back.)

"Hey, how has your holiday weekend break? (Eh. Got a lot of things done, but still need to grade your lab reports. I'll get to them this weekend.)

Physics quiz question: laser diffraction through variable-width single slit

Physics 205B Quiz 3, spring semester 2017
Cuesta College, San Luis Obispo, CA

A red laser (wavelength 632 nm) illuminates a single slit with a width that can be closed or opened. No first minimum fringe would be observed if the slit opening is __________ than 632 nm.
(A) narrower.
(B) wider.
(C) (Neither of the above choices.)
(D) (Not enough information is given.)

Correct answer (highlight to unhide): (A)

From the first minima equation (which uses the angle that measures one-half of the "width of the central maximum on the screen), where W is the width of the slit:

W·sinθ = (1)·λ,

θ = sin^–1(λ/W),

which would give a domain error from the inverse sine function if the quantity (λ/W) is greater than 1, so there would be no first minimum fringe at any angle if the slit opening W is less than the wavelength λ.

Sections 30822, 30883
Exam code: quiz03d3St
(A) : 18 students
(B) : 10 students
(C) : 0 students
(D) : 0 students

Success level: 64%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.26

Physics quiz archive: interference, electrostatics

Physics 205B Quiz 3, spring semester 2017
Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz03d3St



Sections 30882, 30883 results

0- 6 :
7-12 :	* [low = 9]
13-18 :	*****************
19-24 :	******** [mean = 18.6 +/- 4.4]
25-30 :	** [high = 27]

Online reading assignment: diffraction, charges and materials

Physics 205B, spring semester 2017
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 diffraction and charges and materials.


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.

"Diffraction is the spread of light from a single slit."

"Due to the diffraction minima equation, if there is a smaller slit opening, it would result in an increase of the spread of the diffracted waves and if you make the slit opening larger, it would result in decreasing the spread of the diffracted waves."

"Electrons in an insulator are constrained to their atoms, while a conductor has atoms that are more free to move around."

"When a neutral insulator (the electrons are pretty fixed in place) is placed near an object that has a charge there is a net attraction depending no matter what the charge is of the object. If a conductor (the electrons are way more free-moving) is placed near a charged object the electrons move away if it is negative or towards the object if it is positively charged."

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.

"I don't understand why it is that the smaller slit gets a larger spread or vise versa."

"The mobility of electrons part was a bit confusing for me."

"I am having trouble understanding how a neutral insulator or conductor has always has a net attraction towards a charged object, regardless if it is negatively or positively charged.

Match the single slit parameter with its symbol. (Only correct responses shown.)

Width of a single slit: W [96%]
Any positive or negative non-zero whole number: m [76%]
Distance from the slit to a projection screen: L [84%]
Wavelength of light passing through the slit: λ [96%]
Direction, as measured from the centerline: θ [60%]
Position along screen, as measured from the centerline: y [48%]

A gas pump fire is inadvertently caused by the sudden discharge of an electrical spark. Describe when and how the woman became electrically charged.

"She became electrically charged after she got in and out of her car. This likely occurred as she adjusted her sweater because her hands were rubbing the electrically neutral fabric."

"What kind of sorcery is this?!? But I think she was able to transfer a change in electrons from clothes to spark a fire."

"When she is getting out of the car and as she slides across the seat she becomes charged."

"The lady became statically charged when she sat in her car. She could have de-charged by touching something metal to ground herself."

"This is one of my biggest fears, so I always make sure to touch something metal before I begin pumping gas

Electrically neutral polystyrene "packing peanuts" would be attracted to a cat that has __________ charge.

a positive.	* [1]
a negative.	* [1]
either a positive or a negative.	********************** [22]
zero (neutral).	[0]
(Unsure/lost/guessing/help!)	* [1]

An electrically neutral aluminum soda can would be attracted to a balloon that has __________ charge.

a positive.	[0]
a negative.	** [2]
either a positive or a negative.	*********************** [23]
zero (neutral).	[0]
(Unsure/lost/guessing/help!)	[0]

Electrically neutral polar molecules in a water stream would be attracted to a comb that has __________ charge.

a positive.	* [1]
a negative.	** [2]
either a positive or a negative.	********************* [21]
zero (neutral).	* [1]
(Unsure/lost/guessing/help!)	[0]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"Very cool to see different types of everyday things that people use or do and see physics out of it!"

"Practicing diffraction minima examples would be helpful."

"I did not feel as comfortable with the diffraction minima part of the blog. Why is the 'm' value equal to 1? Also, do minimas get categorized with a number like maximas do?" (Mathematically using m = 0 in the diffraction minima equation would give you a dark spot at θ = 0°, which is not what happens physically as the center is always bright, so we "disallow" using m = 0. Using m = 1 gives you the first minimas (dark spots) on either side of the central spot, which is effectively the "spread" of light on the screen. There are other dark (and faint light) spots farther out from the center, and so the locations of these (relatively unimportant) dark spots are given by higher values of m = 2, 3, 4, etc., until you get to θ = 90°.)

"I am slightly confused about using a hair in lab to diffract laser light--will it diffract light the same way as if it was going through a slit of the same size?" (Yes, due to Babinet's principle, light spreading out through a small opening will create the approximately same diffraction pattern as light wrapping around a small obstacle. If you think about light going through a small opening, it is curving around each side of the opening, causing light to spread out from the center. So when you look at light encountering a small obstacle, it will curve around each edge of the obstacle (and cross paths), effectively causing light to spread out from the center (ignoring most of the direct light that passes on either side of the obstacle that doesn't "wrap around" the edges of the obstacle).)

Physics quiz archive: interference, electrostatics

Physics 205B Quiz 3, spring semester 2016
Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz03Ccf7



Sections 30882, 30883 results

0- 6 :	** [low = 6]
7-12 :	***********
13-18 :	******
19-24 :	*************** [mean = 18.8 +/- 7.2]
25-30 :	****** [high = 30]

Online reading assignment: diffraction, charges and materials

Physics 205B, spring semester 2016
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 diffraction and charges and materials.


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.

"The relationship between slit width and destructive interference angles. I sort of skimmed past the electrostatic charge stuff, so I think I understand what's going on, but I'll have to go back and reread it."

"The basic concepts of diffraction, and charges. But I am overwhelmed and confused by the material that has built up to this point."

"In cases with a single slit there are two relevant parameters: the wavelength and the slit opening width. These parameters affect how the waves diffract and spread out (shown by a half-angle θ). In all cases with single slit diffraction there is a faint dark region that is a destructive region that separates the two sides, this is the first minima angle."

"Smaller W results in more diffraction and a larger W results in less diffraction."
"In an insulator, valence electrons are able to move to different positions relative to the atom, but they remain relatively fixed; there is no movement of electrons from atom to atom (For the most part). In a conductor, valence electrons are able to move freely throughout the entirety of the material, from atom to atom."

"In an insulator the outer electrons are fixed to their atomic locations but can move around these locations. In a conductor the outer electrons are more free to move around the whole material."

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.

"Still confused between minima and maxima."

"For once I think I'm pretty okay with the concepts. It's probably thanks to my chemistry background, but nothing really confused me."

"The net attraction of insulators and conductors. I can't really visualize the net forces, and I'm really confused on the negative and positive attractions."

"Nothing at all."

"Cows."

Match the single slit parameter with its symbol. (Only correct responses shown.)

Width of a single slit: W [76%]
Any positive or negative non-zero whole number: m [65%]
Distance from the slit to a projection screen: L [57%]
Wavelength of light passing through the slit: λ [78%]
Direction, as measured from the centerline: θ [51%]
Position along screen, as measured from the centerline: y [46%]

A gas pump fire is inadvertently caused by the sudden discharge of an electrical spark. Describe when and how the woman became electrically charged.

"The woman became electrically charged when she got back in her car and the fabric she is wearing rubbed against the seat. She either lost, or gained electrons."

"The jacket that the woman has on is charged after she sits down and gets back up, therefore once she came in contact with the neutrally charged gas nozzle the electrons were transferred between the nozzle and woman, resulting in igniting the gasoline."

"I don't know."

"Need help!"

Electrically neutral polystyrene "packing peanuts" would be attracted to a cat that has __________ charge.

a positive.	***** [5]
a negative.	****** [6]
either a positive or a negative.	******************* [19]
zero (neutral).	**** [4]
(Unsure/lost/guessing/help!)	*** [3]

An electrically neutral aluminum soda can would be attracted to a balloon that has __________ charge.

a positive.	******** [8]
a negative.	**** [4]
either a positive or a negative.	********************* [21]
zero (neutral).	* [1]
(Unsure/lost/guessing/help!)	*** [3]

Electrically neutral polar molecules in a water stream would be attracted to a comb that has __________ charge.

a positive.	*** [3]
a negative.	*** [3]
either a positive or a negative.	************************* [25]
zero (neutral).	[0]
(Unsure/lost/guessing/help!)	****** [6]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"Why there is destructive interference at first minima for diffraction?" (Ideally a double slit is just two point-like (in phase) sources of light. However, a single slit is just a continuous line of many point-like sources of light that all start in phase, but they cannot all be lined up for constructive interference if θ ≠ 0°, due to all their different path lengths. So only the central θ = 0° maxima will be bright, but eventually the collective constructive interference of this continuous line of point-like charges dies off when you get to the first minima angle off to the side.)

"That video where the girl goes back to her car and it starts going up in flames--I want to know the reason behind this. I feel it could have been her either using her cell phone or sitting back down. Which one is it though? I have the tendency of going back into my car and using my cell phone, so now I'm a little paranoid." (Just remember not to sit down inside and then get back out of your car while filling up. But it's okay to use your cell phone--just remember to take a selfie if you do accidentally ignite the pump.)

"Leap year!"

Presentation: diffraction

Look at this fire hose nozzle. Just look at it. Pinching the flow of water makes it spread out more; while opening up the nozzle narrows the spread of water.

This is not meant to be a technically correct explanation for what we will see with waves that move through a single opening, but this very crude analogy will serve our purposes well enough.

Previously we considered the interference of waves from separate in phase sources, as monochromatic (same wavelength λ light) through two slits. Here we look at diffraction, which is the spread of light from a single slit.

First, terminology.

Notice how these parallel water wavefronts spread out after passing through the central opening in this inlet. This is an example of how waves diffract as they pass through a "single-slit" opening.

The relevant parameters are the wavelength λ of the parallel wavefronts and the slit opening width W, which affect how these waves diffract and spread out, given by the "half-angle" θ, as measured from the center line.

Second, quantifying the spread of these waves after diffracting through the singe slit.

If you squint (in order to increase the contrast of the diffracted wavefronts), you can make out a faint destructive region on either side of the center line, which forms the boundary of most of the diffracted wave energy. This is the first minima angle θ.

The equation for this diffraction minima is given by Wsinθ = mλ, where θ is the "half-angle" of the spread of the diffracted waves, and m = 1 (which if this doesn't freak you out by the resemblance to the double-slit maxima equation, it should). Just work with this, and let's see what it can tell us.

Since the slit width W and spread half-angle θ appear on both sides of the first diffraction minima equation, then making the slit opening smaller would result in increasing the spread of the diffracted waves.

Also making the slit opening larger would result in decreasing the spread of the diffracted waves.

An example of this is the diffraction of light through the circular aperture of a telescope with a "width" W (although the more correct equation in this case would have a correction for a diameter of a circular opening: Wsinθ = (1.22)(1)λ). This is the Whirlpool Galaxy M51 as seen by the NASA Spitzer Space Telescope and the European Space Agency Herschel Space Telescope, as observed with the same infrared wavelength λ. As the Spitzer Space Telescope has a much smaller mirror diameter, light from each part of the galaxy will diffract more and spread out more, resulting in a much less resolved image than from the Herschel Space Telescope, with a much larger mirror diameter, such that light from each part of the galaxy will diffract less and spread out less, resulting in a much better resolved image with finer details left intact.

In laboratory you will shine a laser on your hair. Since the lasers are relatively low-powered (but don't shine them in your eyes), you won't be able to burn through your hairs, but light will diffract around either side of the hair shaft. This turns out to be entirely equivalent to light shining through a single slit of the same width as your hair, and the resulting diffraction pattern on a distant screen shows the spread of light contained within the first minima θ angles on either side of the center line. Depending on how thick your hair is will determine how little (or much) light will diffract and spread out on the screen.