Online reading assignment: diffraction, charges and materials

Physics 205B, spring semester 2015
Cuesta College, San Luis Obispo, CA

Students have a 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.

"Electrons in an insulator are mostly fixed in location, but can move around slightly. When a charged object is introduced, the particles can shift so that opposite charges attract and like charges repel. The same occurs in a conductor, although the electrons are less bound. The same thing happens with polar molecules as well. In all cases, the particles orient themselves to that like charges repel and opposites attract."

"The smaller the slit width (a) the larger the spread (θ). This is why telescopes with larger mirrors are more clear because the light diffracts less in them. Neutral insulators can be attracted to a positive or negative object because the electrons will move and it will cause the attractive force to be greater than the repulsive force.This goes for polar molecules and conductors too."

"I understand the mobility of electrons for an insulator, conductor, and polar molecule. I understand that an insulator has bound electrons, a conductor has free electrons and a polar molecule has free orientation to align it's self in different positions."

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 how that person lived through putting all those packing peanuts on the cat."

"I found derivations of the minima equation confusing, mostly because I know I am going to mix it up with the equation for a double slit experiment."

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

Width of a single slit: a [78%]
Any positive or negative non-zero whole number: m [68%]
Distance from the slit to a projection screen: D [68%]
Wavelength of light passing through the slit: λ [85%]
Direction, as measured from the centerline: θ [44%]
Position along screen, as measured from the centerline: x [37%]

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 could have gotten electrically charged when her feet rubbed the carpet of her car, or maybe when her jeans made contact with the cloth seat. She then discharged when she came in contact with the metal nozzle, created a spark and the gas fumes coming out of the tank combusted."

"Sitting down in her seat probably caused her to become positively charged or negatively charged because the electrons transferred one way or another."

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

a positive.	****** [6]
a negative.	**** [4]
either a positive or a negative.	*************************** [27]
zero (neutral).	* [1]
(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.	*** [3]
either a positive or a negative.	************************* [25]
zero (neutral).	** [2]
(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.	****** [6]
either a positive or a negative.	************************** [26]
zero (neutral).	** [2]
(Unsure/lost/guessing/help!)	**** [4]

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

"ಠ_ಠ Look at this comment, just look at it ಠ_ಠ"

"I hope we go over a·sinθ = m·λ."

"I find it comical that people start fires with static electricity filling gas tanks while I have observed individuals filling their gas tank while smoking and have never had an incident (yet)."