Online reading assignment: circuit basics

Physics 205B, spring semester 2018
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.
"That current is positive charges that circulate per time, also referred to as amps. When the positive charges flow in the clockwise direction the negatively charged electrons flow in the opposite direction."

"A resistor uses up voltage in the circuit."

"I understood the introduction of Ohm's law since I was introduced to it in a previous physics course. I understand how it applies to circuits."

"Good conductors are poor resistors (conductance is inverse of resistance). Different materials have different resistance values measured in ohms."

"The idea of a basic circuit and what an ideal battery is supposed to do. I also understand that when stringing together resistors, you add their resistances together. Additionally, ohms law seems pretty straightforward."

"Ohm's law--as the change in voltage increases and resistance decreases, current increases and vice versa."

"Batteries contain different chemicals that result in different chemical reactions that produce differing amounts of voltage. When batteries are stacked the voltages are added together."

"The components of a basic circuit is the source of energy (such as a battery), a resistor, and wiring between them."

"If resistance is low and/or voltage is high, current can be large. Don't lick a stack of 244 9-volt batteries."

"Stacking batteries creates a higher voltage and stringing resistors creates a higher resistance."

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 need to see how to use Ohm's law more, it looks confusing with how the book presents it."

"I don't understand how to calculate the amount of voltage that stacked batteries have."

"I need clarification on voltage and resistors, and why in a conductor do negatively charged electrons move freely?"

"The short-circuit presentation slide."

"What resistors are used for."

"Resistors, and how they use up the voltage within a circuit."

"Why aren't protons mobile in a conductor?"

A wire is used to complete a circuit with a single 9.0 V battery. When a wire is used to complete a circuit with a system of 244 "stacked" 9.0 V batteries, there will be __________ voltage and __________ current, compared to the single 9.0 V battery circuit.
less; less.  [0]
less; more.  **** [4]
more; less.  *** [3]
more; more.  ************************* [25]
(Unsure/guessing/lost/help!)  * [1]

An emf source is connected to a container of water. When salt is dissolved in the water, there will be __________ resistance and __________ current, compared to the pure deionized water circuit.
less; less.  [0]
less; more.  ************************** [26]
more; less.  **** [4]
more; more.  *** [3]
(Unsure/guessing/lost/help!)  [0]

A metal screw completes a "short circuit" with a transformer emf source. This is dangerous due to the very __________ resistance of the metal screw, and the very _________ current flowing through it.
low; low.  ** [2]
low; high.  **************************** [28]
high; low.  [0]
high; high.  *** [3]
(Unsure/guessing/lost/help!)  [0]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I am excited about this topic."

"Thank you! I'm excited to start this unit, my sister is an electrical engineer and if I can understand one-tenth of what she always talks about, I will be happy :)"

"Please go over the examples above. Thanks!"

"So I think I understand the general concepts but I don't get how to find these concepts or values when there are pictorially represented by a electric circuit. So for example when I see a resistor in an electrical circuit I really don't understand how much it affects current and voltage before and after the resistor. I mean what are the values of current and voltage before the resistor and what are the values of current and voltage after the resistor, do they change, I don't know and I would appreciate the help." (I will make sure you get that help in class today.)

"The purpose of a resistor is not clear. The presentation preview says that it uses up the voltage. Is it really that simple?" (Well, basically, yes. "Using up" voltage means that it is taking energy from the current that passes through it. When you plug in a device to a 120 V outlet, the resistance of that device is designed to use up all 120 V provided to it. We'll look at more conceptual details of this later, but that's the main idea (for now).)

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