## 20150320

### Online reading assignment: circuit analysis

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 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.
"Kirchhoff’s junction rule states that the sum of the currents that flow into a junction— any electric connection—must equal the sum of the currents that flow out of the same junction. The junction rule is a consequence of the law of conservation of charge. Since charge does not continually build up at a junction, the net rate of flow of charge into the junction must be zero."

"I understand the basics about Kirchoffs law, it seems very simple, what comes in must come out. And the loop rule where the net change in voltage must equal zero."

"Resistors can be in a series or in parallel. In series the total resistance is the sum of all the resistors in series. In parallel the total resistance is the inverse of the sum of the reciprocals of all the resistors in parallel. When going through a resistor, the electrical potential decreases as you go with the current and rises flowing against the current. You consider whether you are going from negative to positive or positive to negative for potential rises and drops through an emf."

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 was confused as why we would only care about the flow of electrons in a circuit not the direction of the current. I don't get why they wouldn't both flow in the same direction."

"The concepts don't seem all that confusing."

"The rise and drops of electronic potential is hard for me to understand I would like more explanation in class. I would like to see in class problems."

"For resistors in series, voltage drops according to ∆V = I·Rm and yet the same current passes through all the resistors? And for resistors in parallel, they all receive the same drop in ∆V, and yet the current is split between them?"

Determine what happens to the following parameters as current flows through an ideal wire.
(Only correct responses shown.)
Current: remains the same [64%]
Voltage: remains the same [53%]

Determine what happens to the following parameters if you go through a resistor along the direction of current.
(Only correct responses shown.)
Current: remains the same [42%]
Voltage: decreases [58%]

Determine what happens to the following parameters if you go through into the (-) terminal and out of the (+) terminal of an ideal battery.
(Only correct responses shown.)
Current: remains the same [42%]
Voltage: increases [42%]

Briefly explain what quantity is conserved when applying Kirchhoff's junction rule.
"The sum of the currents into or out of any junction in the circuit is zero."

"Charge flow per time is conserved."

"Current is conserved."

"Charge is being conserved. Thus the currents into a junction must equal the sum of all currents flowing out of that same junction."

Briefly explain what quantity is conserved when applying Kirchhoff's loop rule.
"Electric potential energy per charge."

"Electric potential is conserved. For any path in a circuit that starts and ends at the same point the sum of electric potential change is zero."

"Voltage is conserved I believe but I am not quite sure."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Is there any way to do one big problem using all the aspects of circuits. if so I would like to do one." (No, baby steps. But each baby step will be gigantic.)

"One of life's rules: Do not become part of the circuit."

"I can't believe we are already half way to the end of the semester. I got a tutor to help me kick butt and take names on the upcoming midterm:-) Could you please give us an idea of what are primary focus of study should be this weekend for the midterm?" (The list of midterm-like problems is now posted, as well as the study guide for the midterm.) "