## 20130326

Physics 205B, spring semester 2013
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.

Selected/edited responses are given below.

Describe something you found interesting from the assigned textbook reading or presentation preview, and explain why this was personally interesting for you.
"The video on how to make a lighter with a battery and a gum wrapper is pretty cool! Definitely gonna try that. I'm surprised there is that much heat created."

"I think it's interesting that if the current is split across two parellel resistors, the sum of current running through those resistors is more than the current running through the original wire. Sorry that wasn't the best explanation."

I found it interesting to learn why electricians keep one hand behind their back so they do not complete the circuit and get a charge running through their body."

"How series and parallel circuits work."

"Reading about energy in circuits was interesting to me. Energy has always been interesting, and I am excited that we are learning a little about it."
"I found out that as more appliances are plugged into the same household circuit, the resistance becomes dangerously low which can cause overloaded outlets and lead to fires. This was personally interesting because I didn't know this could happen in the household."

"I never knew that plugging in multiple sockets to an outlet decreases the resistance. Interesting."

"Runaway current is an interesting topic because some people do stupid things like trying to plug in too many things into an outlet."

"I thought it was interesting how they make electric fences. By touching the fence you complete the circuit through yourself and the ground and get a nasty shock."
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"I am a little confused about the I2·R equation and how to use it."

"Still confused on a lot of the equations, trying to remember what all the symbols stand for."

"Confusing how to combine series and parallel circuits."

"Ammeter and voltmeters, I don't quite follow."

"I'm confused about the difference between power and energy. Just because they are so similar."

"I am confused on what exactly causes the fire with the gum wrapper and battery."

"Although energy is interesting, I find it confusing as well. Also reading about the effects of an electrical current on the body made me realize how dangerous electricity really is."

"The equations. They are always confusing to me. So many freaking letters; I want to punch the computer. I feel like I have a better grasp on concepts when I read the blog.

"Power dissipation."
Plugging in and using additional electrical appliances in the same household circuit would increase the total __________ in the wiring inside the house.
current. : 17 responses
voltage. : 2 responses
(Both of the above choices.) : 1 response
(None of the above choices.) : 0 responses
(Unsure/guessing/lost/help!) : 4 responses
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"The power dissipation equation seemed simple enough, but is the final answer work = joules per second?" (Yes, and joules per second is also watts.)

"I am having a hard time separating power from energy. The textbook says that power is the rate at which energy conversion takes place?" (Yes. Energy is energy. The rate at which energy is used per time is power. Think of money as money. The rate at which money is spent per time is...scary.)

"I was confused about the difference between the ampere and the watt, is the ampere so much wattage passed per time?" (Watt? Anyways, charge is charge. How much charge flows per time is current, measured in amperes. And energy is energy; how much energy is used per time is power, measured in watts. Units can get pretty crazy in electromagnetism, and we're not done yet.)

"One time I had a car battery in the back of my truck and I was driving and saw a flash and thought it was just a reflection but then I went around this turn and I saw a spark in the back of my truck. I pulled over and found that a grounding rod had rolled on top of the battery and was connecting the terminals, the end of the grounding rod burned through my truck liner....crap!" (Yes, shorting out a car battery (as was done in the first season of Breaking Bad) is basically much more dangerous version of using a gum wrapper to short out a AA battery.)