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 capacitors.
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.
"The concept of the capacitor charging: in the GIF animation, the charging seems to be due to a negative charge leaving one side and when the negative charge leaves, a positive charge is left over. The positive charge then attracts a negative charge in the opposite side of the capacitor."
"The SI unit of capacitance is a farad, or coulombs squared over joules. Also that the capacitance is fixed once the construction of the capacitor is complete, and the only way to change the capacitance is to change the build of the capacitor. The potential applied to the capacitor can be altered however by using different batteries."
"A capacitor constructed from two plates and a space in-between. I also understand the capacitor construction formula."
"That once a capacitor is constructed you cannot change the capacitance of it without changing its build (plate area or separation distance)."
"Capacitors are built by putting parallel metal plates together with a small distance in between. Charging a capacitor requires a battery and will cause electrons to move freely from the top plate to the bottom plate until the top plate demonstrates a positive charge and the bottom plate have a negative charge. However, as more and more electrons move towards the bottom panel, it requires more work and creates a larger EPE charge due to the voltage."
"Capacitors store electric charge. Capacitors have a capacitance, which reflects their ability to store electric charge. While their capacitance is determined by surface area and separation distance of parallel metal plates, changing the voltage applied to the capacitor also changes their charge but does not change the capacitance of the capacitor."
"Capacitors store up electric potential energy by creating a potential difference across 2 parallel metal plates. The more charge the capacitor holds, the more energy it takes to move it across to the opposing plate. Unlike batteries, a charged capacitor can release its energy in a short burst over a short period of time."
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.
"Understanding voltage and especially understanding how it relates to capacitance is difficult."
"I don't understand how a capacitor gets charged."
"I do not understand capacitor charge because I see charges staying or leaving."
"Electric potential energy storage explanation."
"The capacitor energy storage formulas were different depending on the scenario. I need to work problems out to understand the differences."
"I found most of this reading assignment confusing. I could definitely use some clarification on the math."
"Nothing at this time, just want more examples of applications in class."
Describe two quantities that a capacitor is designed to store/hold.
"A capacitor is designed to hold voltage and electric potential energy."
"The capacitor holds charges. Both positive and negative?"
"Charge and electric potential energy."
State the unit of capacitance, and give its definition in terms of other SI units.
"farad, F, which is C (coulombs) squared divided by joules."
"Coulombs/volts = farads; where coulomb is electric charge, while volt is electric potential."
decreasing; decreasing. [0] decreasing; increasing. ** [2] increasing; decreasing. ************************ [24] increasing; increasing. *** [3] (Unsure/guessing/lost/help!) *** [3]
For a parallel-plate capacitor, increasing the voltage (electric potential) difference applied to the capacitor would __________ the amount of charge stored in it.
decrease. ******* [7] increase. **************** [16] have no effect on. ******* [7] (Unsure/guessing/lost/help!) **[2]
Explain why increasing or decreasing the voltage (electric potential difference) of a capacitor cannot change the numerical value of its capacitance.
"I don't know. I would think increasing the voltage also increases the capacitance?"
"Because it only affects the actual amount of charge it has, not the storage ability, or size of the actual capacitor."
"The capacitor is based on the plate separation distance and cross-sectional area."
"The capacitor holds a specific amount and adding or decreasing the voltage does not change. This is due to the fact that once it is constructed, the capacitance is fixed."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Do we get to use capacitors in any labs?"
"I am definitely struggling with this section, are we going to take a pretty deep dive on this?" (We will, but in lab.)
"Oh man, this electricity stuff is challenging."
"Capacitors shockingly weren't as difficult as I was anticipating."
"I noticed that farads are named after Michael Faraday. I hear his name mentioned a lot when discussing physics. Has he made a lot of contributions to the physics of electricity?" (Yes, but so did a lot of other physicists that have units named after them: Coulomb, Volta, Ohm, Ampere, Weber, Henry, and Tesla; along with others who don't have units named after them: Franklin, Maxwell, Ørsted, Lorentz, etc.)
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