## 20150309

### Online reading assignment: electric potential energy

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 electric potential energy.

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.
"How electric potential energy would increase for pushing like charges together and for pulling opposite charges apart. This is due to the work required to hold each charge either together or away from each other."

"For electric potential energy there is a direct approach, and a two-step approach. In the direct approach the source q1 stores UE with test q2, where as in the two-step approach the source Q creates V potential which then stores UE with test q.

"There is something called potential V and something totally different but related called potential energy (UE). I understand that the field lines always point towards decreasing potential but that for a negative test charge this is also the direction of increasing potential energy while for a positive test charge its decreasing potential energy."

"All I really understand is that an electric field is present around all charges."
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.
"he equipotential surface in relation to the electric fields and electric potential were a bit confusing. It says, 'if equipotential surfaces are drawn such that the potential difference between adjacent surfaces is constant, then the surfaces are closer together where the field is stronger,' but I don't quite understand how."

"I'm honestly lost on most of the models presented in this reading assignment. I am finding this material hard to understand and also harder to relate to with real world experience than last semester."

"What's the difference between potential and potential energy?"

"I am still just completely in shock as to how lost I was in the last class and really feel like I was not getting any of the material we were going over. I really could use some more examples of Coulomb's law. Could we also go over some electric potential energy problems in class as well?"

"I understood everything from the reading. From what I read I do not believe anything was confusing and I think I grasped all of the concepts."

"I cannot make the overall picture of how all these different concepts connect--I'm pretty lost I don't know where to begin."

"I'm not sure how the electric potential changes when q and Q move closer or farther together. Is it always an increase because moving them takes energy no matter what way?"

"The concept of equipotentials."

"The equations! They look just like the last presentation...which was confusing. Now we're adding confusing to already existing confusing. Ahh!"
Explain the difference between the units of electric potential V, and electric potential energy, UE.
"The difference between units for electric potential V and electric potential energy UE are that V is in units of V, volts or J/C, where as UE is just in units of J, joules. The difference comes from the fact that different variables are used to calculate the two values."

"No clue. J/C and N·m."

Explain the conceptual difference between the electric potential V, and electric potential energy, UE.
"The difference between electric potential V and electric potential energy UE is that V potential is something that is created and acts upon something else, whereas UE is stored by something and is dependent on V and what is storing it."

"Electric potential V is the energy per unit while electric potential energy is the energy it takes to move a charge in a field."

Briefly summarize the difference (if any) between "voltage" and electric potential.
"Electric potential is often shortened to potential. It is also called 'voltage' especially in connection with electric circuits. No difference, right?"

"idk."

"They are the same! Which is super-confusing if you forget..."

Identify the changes in electric potential energy UE (if any) for the following test charges (±q):
(Only correct responses shown.)
Positive test charge +q brought closer to a positive source charge +Q: increase [61%]
Negative test charge –q brought closer to a positive source charge +Q: decrease [55%]
Positive test charge +q brought closer to a negative source charge –Q: decrease [61%]
Negative test charge –q brought closer to a positive source charge –Q: increase [55%]

Identify the changes in electric potential V (if any) for the following test charges (±q):
(Only correct responses shown.)
Positive test charge +q brought closer to a positive source charge +Q: increase [29%]
Negative test charge –q brought closer to a positive source charge +Q: increase [29%]
Positive test charge +q brought closer to a negative source charge –Q: decrease [26%]
Negative test charge –q brought closer to a positive source charge –Q: decrease [32%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I wonder if that guy in the snowmobile accident got severely hurt?" (I'm sure he's fine--although I can't speak for his snowmobile, or his ego.)

"Why do they have to have so many different names for the same thing and then super-similar names for totally different things?" (Yeah. What's up with that?)

"Well this is definitely the most confusing stuff so far in class to me."

"What in the world is even going on, I'm so confused."

"I think I took too long to understand this section without much avail."

"I need to manage my time better."