## 20160329

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.

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.
"Some of it, but it gets confusing. I think I need to look at more specific instances."

"The differences between series and parallel. I just need to review the different equations and such."

"Ammeters have zero internal resistance, making them dangerous if you wire them into a circuit wrong. The circuit should be 'broken' and the ammeter wired into the gap; connecting it in parallel can cause an unsafe rise in current. Voltmeters can be used to measure the voltage drop/rise across any two points."

"Same good ol' electricity. Don't want too much power going through parallel circuits which is why you have a circuit breaker just in case. [Series] resistance adds up, and you don't want to mess up multimeter readings due to improper placements."

"An ammeter measures current flow and must have zero resistance to not change the circuit it is measuring. A voltmeter simply gives you the pressure difference between any two points and the voltmeter has infinity resistance."

"Placing more resistors lined in-parallel within a circuit will result in a greater chance of accumulating a runaway current. It took me the lab as well as reading to sort of visually see how current can steadily build within a circuit as its resistors are placed in parallel. The spread of current allows for the possibility of there being less potential drop in electric potential energy as current travels through each given resistor in parallel."

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.
" Kirchhoff's rules are a little fuzzy to me but I just have to do some more example problems to fully understand them."

"I still just find resistors and ammeters confusing. Maybe they aren't as complicated and I am making it more complicated than it really is. I just need to go over equations and really get a solid feel for it."

"I'm kind of lost on the application of bulbs and switches, etc."

"Why resistance goes to infinity for a dead battery, or for a burnt-out light bulb."

"I am confused on everything!"

"Nothing particularly."

What are the resistances of these (ideal) devices?
(Only correct responses shown.)
Ideal light bulb: some finite value between 0 and ∞ [65%]
Burnt-out light bulb: ∞ [36%]
Ideal wire: 0 [55%]
Real (non-dead) battery: some finite value between 0 and ∞ [74%]
Ideal switch, when open: ∞ [48%]
Ideal switch, when closed: 0 [48%]

Two light bulbs with different resistances r and R, where r < R, are connected in series with each other to an ideal emf source. Select the light bulb with the greater quantity.
(Only correct responses shown.)
More current flowing through it: (there is a tie) [52%]
Larger potential potential difference: light bulb R [55%]
More power used: light bulb R [29%]

Two light bulbs with different resistances r and R, where r < R, are connected in parallel with each other to an ideal emf source. Select the light bulb with the greater quantity.
(Only correct responses shown.)
More current flowing through it: light bulb r [35%]
Larger potential potential difference: (there is a tie) [35%]
More power used: light bulb r [16%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I appreciate the fact that you had our midterm right before Easter so that our holiday was free and how you're having our quiz this Friday so that our spring break is free. Thank you!" (Thereby ruining my Easter and my spring break. #yourewelcome.)

"This was really confusing!"

"Twinkle twinkle....dang it!"

"I suck at physics. It's ruining my self-esteem."

"Don't April fools me with the quiz. #notcool"

"How can we determine the resistance of certain [ideal/real/burnt out] devices? I'm not sure how to go about evaluating things." (We'll go over these on the worksheets in class.)