20140319

Physics 205B, spring semester 2014
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 circuit analysis.

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.
"When batteries are connected positive terminal to negative terminal in series, this provides a larger emf."

"I understand that electric potential drops when the path direction of a current on a resistor goes downstream, and rises when the path is upstream. I also understand that Kirchhoff's rules deal with the conservation of energy and charge flow."

"What goes in must come out. I may be utterly wrong and could possibly end up face first in the dirt due to this comment, but I'm feeling very confident with the junction rule, loop rule, and concept of 'net zero.'"

"I understand Kirchhoff's rules as some are similar to rules learned last semester. What goes into a current is also what comes out. The loop rule explains how the voltage rises and drops and if a circuit is a traveled in a loop there will be a net zero sum."

"Resistors in series are additive. Resisters in parallel are the inverse of the sum of the inverses of the resistances. Current flow is conserved: what goes in, must come out."

"Batteries: two batteries +- +- provide a larger emf and are added together."

"For most configurations of resistors, an equivalent resistance can be calculated, which represents the value of the single resistor that could replace them without affecting the rest of the circuit."

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.
"Signs, signs, and more signs. No, not the movie with the aliens, crop circles, and Mel Gibson, but the rises/drops in the resistor and emf current examples. I will figure out soon enough, but for right now, I can't differentiate between up and down."

"I am having a hard time comprehending the emf rises/drops. I don't fully understand why the electric potential rises when movement through a battery is towards the positive terminal and vice versa."

"I don't know how to apply Kirchhoff's rules. I get the resistors thing, but not much after that."

State the unit of electromotive force (emf), and give an equivalent definition in terms of other SI units.
"I think the units of electromotive force is volts."

"Volts V = amps·ohms = watts/amps = joules/coulomb."

"Volts, kg·m2·s-3·A-1."

As current flows through an ideal wire, the amount of current __________ and the voltage ___________.
 decreases, decreases. * [1] decreases; remains the same. ** [2] decreases; increases. * [1] remains the same; decreases. ** [2] remains the same, remains the same. *********************** [23] remains the same; increases. * [1] increases; decreases. [0] increases; remains the same. [0] increases; increases. ** [2] (Unsure/guessing/lost/help!) ** [2]

If you go through a resistor along the direction of current, the amount of current __________ and the voltage ___________.
 decreases, decreases. *** [3] decreases; remains the same. ****** [6] decreases; increases. * [1] remains the same; decreases. ************ [12] remains the same, remains the same. ****** [6] remains the same; increases. ** [2] increases; decreases. * [1] increases; remains the same. [0] increases; increases. [0] (Unsure/guessing/lost/help!) *** [3]

If current flows "forwards" through a battery (into the (-) terminal and out of the (+) terminal), the amount of current __________ and the voltage ___________.
 decreases, decreases. ** [2] decreases; remains the same. * [1] decreases; increases. * [1] remains the same; decreases. [0] remains the same, remains the same. ******** [8] remains the same; increases. [11] increases; decreases. *** [3] increases; remains the same. *** [3] increases; increases. * [1] (Unsure/guessing/lost/help!) **** [4]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I'm confused about the function of switches. When they are turned off does the current just stop? And then when they are turned on the current just flows continuously?" (Yes, and yes, assuming we can ignore the brief abrupt changes as current is stopping, or just starting up.)

"What do diodes do?" (They're like one-way valves. Current can flow in one direction, with zero resistance but current flowing back through the other direction would have infinite resistance. Like those no-back-up tire rippers at parking garage exits.)

"For going downstream, is the negative sign there because the voltage is going in a way that it wants to go (lower potential energy) as opposed to upstream in a way that it doesn't want to go (higher potential energy)? If voltage or emf goes up, does potential energy go up?" (Yes, yes, and yes--because voltage or emf is the potential energy...per charge.)

"Way to go, Kirchhoff. You reap what you sow."