## 20150330

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 reviewing presentations on circuit analysis and previewing presentations on advanced electricity concepts.

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 a ammeter measures the current passing through a light bulb while a voltmeter measures the amount of potential used by a light bulb."

"I understood the difference between parallel and series circuits and how to calculate problems using their equations. I also learned to reset your circuit breaker you have to unplug your appliances which is good to know in order to complete a circuit."

"Ammeters have zero resistances, and voltmeters have infinite resistances."

"Current and potential difference in a circuit can be measured with instruments called ammeters and voltmeters, respectively. A multimeter functions as an ammeter or a voltmeter, depending on the setting of a switch and which of its terminals are connected."

"When more appliances are plugged in to an outlet, the resistance will decrease (when can be very dangerous). In addition, we have circuit breakers to prevent current levels from reaching a dangerously high level--if the circuit breaker is triggered, this turns off the electricity so that the wires in the house do not become fried."

"When equivalent resistors are placed in series, the resistors have an additive effect. However, when equivalent resistors are placed in parallel of each other, then the total resistance is the sum of the reciprocals of the resistors added together."

"When you plug in more and more space heaters at your house, the resistance becomes lower and lower. This can become dangerous because it means that the current can flow higher and higher."

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 anything else regarding ammeters and voltmeters. I'm also unsure how to work with equations using Req and current I."

"I dont understand anything with ammeters or voltmeter except one is close to zero and one is close to infinity?"

"I found ammeters and voltmeters to be confusing. I also found combination so series and parallel resistors to be confusing."

"All this electrical stuff is very confusing to me and a bit uninteresting."

"I was confused as to why a circuit would have to be broken open if connected to a ammeter. Also was confused as to what power dissipation is."

"Ohm's law parameters. It's just a very new 'language' to me. So trying to understand exactly how they really work together is weird."

"For some reason the connection between I and ∆V is still unclear."

"Lots of equations, not sure when to use which. I think I understand how the different terms can be substituted to relate some of the equations to each other, but the applications of the equations are a little confusing."

What are the resistances of these (ideal) devices?
(Only correct responses shown.)
Ideal ammeter: 0 [71%]
Ideal voltmeter: ∞ [63%]

Determine what will happen to the following parameters when additional electrical appliances are plugged in and turned on in the same household circuit.
(Only correct responses shown.)
Equivalent resistance Req of circuit: decreases [49%]
Current I flowing through emf source: increases [41%]

A fuse or circuit breaker is designed to prevent too much __________ in household wiring.
 current. ******************************* [31] voltage. **** [4] (Both of the above choices.) * [1] (Neither of the above choices.) [0] (Unsure/guessing/lost/help!) *** [3]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Felt pretty great about the midterm. Did a little better than last semester's midterm."

"I am kind of lost here and would benefit from a lot more help in class."

"Just so I have this straight. A voltmeter and ammeter are the same instrument but when the wiring of a circuit is open and we are measuring the current the voltmeter becomes an ammeter?" (Yes, but don't forget to change the dial settings on the multimeter to tell it to change from a voltmeter to an ammeter.)

"Are you ready for spring break, yet?" ("The mountains are calling, and I must go.")

"Welding circuits typically range from 70-200 amps. Dangerous stuff is so fun."