## 20140309

### Online reading assignment: electric potential energy

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 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.
"UE = 0 when particles are infinitely far apart. Electric force on a charge is always directed toward regions of lower electric potential energy."

"Based on the presentation, I understood that electric potential energy can be increased by either pushing together like charges or pulling apart opposite charges. Electric potential energy decreases by either pulling apart like charges or pushing together opposite charges."

"Surprisingly, solving problems using just about all of the electric potential energy equations is coming quite easily right about now. Funny, because while I am able to plug in the numbers, my actual understanding of the concepts in this section need some work, to be sure."

"Honestly, I'm completely lost and don't really understand these chapters."
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 am finding it difficult to apply the formulas."

"I am having a hard time understanding the difference between potential and potential energy. I am also having a hard time understanding why as you get further away from a positive source the potential decreases, and why if you get closer to a negative source the potential also decreases."

"What I find confusing is the interconnection of potential, potential energy, electric forces, and electric fields. I understand they are different but after reading the material they all melt together. Going over these would be really helpful in class. Also what charges do to each other based on how they effect the change in potential."

"How to use force models and coulombs law in a problem. A better understanding between electric forces and electric fields and their purposes."

"The equipotential stuff was a bit confusing."
A pair of charges are to be brought closer to each other. As a result, which pair of charges will increase their electrical potential energy?
 A +2 nC charge and a +2 nC charge. ************************** [26] A –2 nC charge and a +2 nC charge. ** [2] (Both of the above choices.) [0] (Neither of the above choices.) [0] (Unsure/guessing/lost/help!) ** [2]

Briefly explain your answer for the previous question (comparing changes in electric potential energy).
"When the same charges are brought together, they repel each other. Therefore as they get closer together, their electric potential energy increases."

"I would think that the –2 nC and +2 nC charges would cancel each other out. And that would yield a neutral charge. I'm not a hundred percent on this though."

Explain the difference between the units for electric potential V, and electric potential energy, UE.
"V is the electric potential energy per unit charge, and UE is the electric potential energy as a function of the position of the movable charge."

"The units of electrical potential are in volts or J/C and potential energy is in units of joules."

Explain the conceptual difference between the electric potential V, and electric potential energy, UE.
"I am having a hard time with this concept. What I do know are the definitions. Electric potential is the energy stored in an electric field. Potential is the electric potential energy per unit charge."

"Potential is a measurement of potential energy per unit charge while electric potential energy is the total energy stored in an electric field."

"Yeeeahh...just a tad lost on this as well."

Briefly summarize the difference (if any) between "voltage" and electric potential.
"None."

"Voltage and electric potential really mean the same thing. There is no difference."

"1 V = 1 J/C Electric potential is measured in volts. Voltage is an informal name."

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 [93%]
Negative test charge –q brought closer to a positive source charge +Q: decrease [80%]
Positive test charge +q brought closer to a negative source charge –Q: decrease [80%]
Negative test charge –q brought closer to a positive source charge –Q: increase [77%]

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 [50%]
Negative test charge –q brought closer to a positive source charge +Q: increase [43%]
Positive test charge +q brought closer to a negative source charge –Q: decrease [60%]
Negative test charge –q brought closer to a positive source charge –Q: decrease [53%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Not looking forward to the quiz on Wednesday." (Can't we just call it a "celebration of learning?")

"I'm extremely lost, a formal lecture would really help. Can we please clarify the difference between electric potential energy and electric potential?" (Imma try.)

"This chapter is THICK! Lots of visuals would be great. Do you have any good websites to check out?" (Check out this video, which may help...or not. In any case, enjoy the ride.)