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 basics.
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.
"Most basic circuits that we can build will have an electromotive source of voltage connected to the resistor. In this way the charges can flow continuously around and around. I also learned that an ideal battery uses the chemical reactions that occur change charges in an order to release electric potential energy. I also learned that different chemical reactions will release different amounts of electrical potential energy which creates different voltages."
"An ideal circuit is one where charges can flow continuously through it. Electrons flow in the opposite direction of the current, which is how much positive charge in coulumbs that circulates per time in seconds. Coulombs per second is referred to as amps. Ideal batteries are used to release electric potential energy by exchanges charges. A circuit also consists of a resistor in which all different materials have different resistance values. We can use Ohm's law to determine how much current will flow through a circuit."
"When you stack ideal batteries, you add the total value of voltages. A good conductor has a low resistance value and a poor conductor has a high resistance value. When you string together resistors, you have to add their individual values together for an equivalent resistance value. Ohm's law can help determine how much current will flow given the total amount of voltage and resistance."
"In a basic circuit, charges can flow continuously around. A current is the positive charge that circulates while the electrons will flow around the other way."
"A basic circuit involves an electromotive force connected to a resistor so that a charge may flow continuously. A current is defined by the amount of positive charge flowing (out from the (+) terminal of the battery), but it is the electrons that are flowing in the opposite direction (out from the (–) terminal of the battery)."
"Amps (A) is what a positive current charge that circulates in coulombs per second."
"There is a direct relationship between resistance, voltage and current. These three variables describe different characteristics of a circuit. The equation is able to be manipulated easily to solve for the desired variable."
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 don't understand the idea of battery stacking in order to increase the voltage output. Does the electric current just flow between the batteries, how do the stacked batteries relate to each other in order to increase the voltage output?"
"What is amperage and how is it measured in contrast to voltage? Why are these two aspects inversely related and how does that apply to each circuit?"
"I think I'm understanding the basics, but it also feels like I'm really missing something."
"We hear AC/DC all our lives (not the band necessarily). I don't know that I've ever realized how simple that concept really is. Direct current is moving one way all the time and alternating current is alternating back-and-forth. what a concept!"
"For some reason this is really hard for my brain to wrap around. I get the basic concepts of how a circuit functions, but when it comes to amps and current and voltage and stuff like that."
"Ohm's law--I do not understand the difference between the voltage and the current. Also I do not understand why the ratio of ∆V/I remains constant."
"I am sorry, I will read this before class. Chemistry is killing me :("
"I need to be more in-depth with all the material in this reading."
"I will take great notes in class on Monday."
less; less. * [1] less; more. ** [2] more; less. ****** [6] more; more. ********************** [22] (Unsure/guessing/lost/help!) ***** [5]
less; less. [0] less; more. **************************** [28] more; less. ** [2] more; more. * [1] (Unsure/guessing/lost/help!) ***** [5]
low; low. * [1] low; high. *************************** [27] high; low. * [1] high; high. ** [2] (Unsure/guessing/lost/help!) ***** [5]
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I didn't quite understand what you meant by 'current flowing clockwise through this circuit, while the electrons actually circulate in the opposite counterclockwise direction through this circuit.' Does this mean that the negative charge (electrons) is going one direction and the positive charge (protons) is going the opposite direction?" (Almost; electrons are traveling in one direction around the circuit, and the lack of electrons (which makes a neutral object have a positive charge) travels around in the opposite direction. You can think of bumper-to-bumper traffic, where each car moves forward, but the gap between cars moves backwards down the freeway.)
"So the current moves in one direction?" (For the steady-state, direct current circuits (which we are considering here), the current keeps moving in one direction around the circuit, at a constant value. However, what is really going on is that electrons are going in the opposite direction of how we define currents, but that's a result of electrons arbitrarily being labeled as having a negative charge instead of positive charge.)
"This was very helpful. The circuits seem super-dangerous." (These were only dangerous not just because of the voltage differences, but because the resistances were low, making the resulting amounts of current very high.)
"I don't understand if short-circuiting is due to too much or too little resistance." (Too little. Even with a modest amount of voltage (∆V), completing a circuit with a low resistance object (metal, water, unprotected sweaty palms) will make the resistance (R) in the denominator in Ohm's law (I = ∆V/R) very small, making the current (I) very high, which is what can kill you.)
"Can you explain what happens when you are putting up your Christmas lights and one bulb is dead then the series of bulbs after it don't work." (If a bulb completely burns out ), then no current can pass through it (as its filament is broken), which prevents the rest of the bulbs from being lit, as the circuit is now "open." However, a newer "shunt" type of bulb has a backup path for current to pass through it even after the filament is broken, although you may notice the rest of the bulbs are a little dimmer afterwards.)
"I'm curious to how my portable charger works and what makes it so easy to charge as well as why it charges the phones so fast in addition to lasting so long to die off. I'm curious to know what materials they used, but of course I'm not going to dismantle it to see what's inside." (Most likely it contains a lithium-ion battery inside. And yes, good on deciding to not take it apart.)
"I am just a little confused on the stacking component of batteries (and even batteries in general). I understand there is a chemical reaction but how does that create a charge? Do batteries constantly have a charge and chemical reactions are happening inside the battery at all times?" (By "charge" let's make sure we're talking about actual electrons that flow, instead of "putting energy into" the battery. So chemical reactions occur in batteries by materials exchanging electrons (to fill or to empty their orbitals and bonds), releasing energy in the process. If the battery is part of a complete circuit, then electrons are free to flow through the rest of the circuit to return to the battery, and take part in further chemical reactions, releasing more energy, etc. Ideally, if the battery is disconnected from a circuit, then the chemical reactions will stop, because no more electrons are available to be exchanged.)
"It would be cool to make a battery for lab." (That sounds like chemistry to me. However, we'll be building a capacitor in lab this week, and taking a look at thermocouples for next week's lab, which can basically be thought of as temperature-dependent batteries.)
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