## 20170317

### Online reading assignment: circuit analysis

Physics 205B, spring semester 2017
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.

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.
"Circuits in series don't work if one light bulb fails like in Christmas lights. Parallel wiring will allow the circuit to keep working if one of those fails."

"What I was able to understand from tonights reading was that resistors can be in a series or in parallel. If the resistors are in series then the total resistance is the sum of all the resistors in series. If the resistors are parallel to one another then the total resistance is the inverse of the sum of the reciprocals of all the resistors in parallel."

"I understand why I is constant throughout the circuit, amperage will not change, described by the junction rule. It can separate, but the sums will remain the same."

"What I really understood from the reading was equivalent resistances. I understand that in a series the R equivalent will go up while in a parallel the equivalent resistance will go down."

"From what I understand, the more resistors that you have in series will increase the equivalent resistance. For resistors that are in parallel, the more you have will decrease the equivalent resistance because the resistance is calculated as the reciprocal of the sum of the reciprocals."

"Kirchhoff's rules are easy to understand and to put to use. We are slowly putting together the rules of electric circuits. The quiz examples online are great examples as well."

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.
"What I need more explanation on is the potenital drops/rises and the emf drops/rises. I did read over the textbook and it seems to make things a bit more clear, but I still don't feel comfortable with it totally."

"I don't fully understand the math involved in parallel vs. series resistors. The examples on a conceptual level made sense, but why its the addition of reciprocals I don't know."

"What I found confusing about tonight's assignment was the rise and drops of electronic potential. The concept for me was difficult to understand I would like more explanation in class."

"The rise and falls of electronic potential are kind confusing for me. An example in class would be really helpful."

"The material I don't really understand right now would be Kirchhoff's rules such as the junction and loop rule."

"A lot of things, as usual."

"I do not struggle with electricity because I think of it like water."

"It all made a lot of sense."

Determine what happens to the following parameters as current flows through an ideal wire.
(Only correct responses shown.)
Current: remains the same [86%]
Voltage: remains the same [45%]

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 [64%]
Voltage: decreases [73%]

Determine what happens to the following parameters if you follow a path (regardless of current direction) into the (–) terminal and out of the (+) terminal of an ideal battery.
(Only correct responses shown.)
Current: remains the same [73%]
Voltage: increases [55%]

Briefly explain what quantity is conserved when applying Kirchhoff's junction rule.
"The amount of current put in is the same as the amount of current that exits."

"The quantity that is conserved when applying Kirchhoff's junction rule is that the charge is being conserved. The current that is going into a junction has to be equal to the sum of all the currents flowing out of the same junction."

"Voltage is observed when applying the junction rule?"

Briefly explain what quantity is conserved when applying Kirchhoff's loop rule.
"Voltage is conserved. The voltage drop experienced along the circuit must equal the voltage rise supplied by the battery/emf source."

"In closed loops the sum of the potential differences across all elements is zero. This law is a statement of energy conversation."

"The quantity that is being conserved when applying Kirchhoff's loop rule is that electric potential is being conserved. What I understood it to mean is that for any path in a circuit that starts and ends at the same point, the sum of electric potential change is zero."

"Voltage."

"Current is observed when applying the loop rule?"

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Please go over parallel versus series circuits."

"I am confused why connecting resistors in parallel would decrease the equivalent resistance, while connecting them in a series would increase it. I am confused on the reasoning behind it, not the equation itself." (Think about a resistor as a check-out counter at a grocery store, and the flow of customers is the current. Check-out counters at a grocery store are set up in parallel to create a low "resistance," so each customer can go through them once in multiple lines and leave. However, if all the check-out counters were set up in series, such that every customer would need to go through all of them in a single line, and that would mean a very high "resistance.")

"I don't understand why moving from the negative terminal towards the positive terminal in a battery (or vice versa), determines an increase (or decrease) in voltage. I also don't understand how humans can act as a wire simply by touching each other." (Think about positive and negative charges as being peaks and wells of electric potential. If you travel from negative to positive, you are experiencing an increase in electric potential, as you are "climbing uphill" from out a a "well" to a "peak." This is how current experiences an increase in volts as it goes in the negative terminal of a battery, and out the positive terminal of a battery.)

"Are the increases or decreases in voltage caused by the direction in which electrons or moving?" (No, the increases or decrease in voltage are caused by the source charge(s) (in the case of a battery, the chemicals inside), resulting in conceptual "peaks" or "wells" in electric potential. The flow of positive test charges (like current) will move "down" an electric potential slope, while negative test charges (like electrons) will move "up" an electric potential slope. So, the electric potential is not set by how the test charges flow, but how the test charges flow depends on the electric potential.)