## 20160314

### Online reading assignment: circuit basics

Physics 205B, spring semester 2016
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.
"The addition of compounds to water can increase its conductivity."

"The current in a circuit can be determined if the quantity of charge Q passing through a cross-section of a wire in a time t can be measured. The current is simply the ratio of the quantity of charge per time."

"Current is measured in amperes (coulombs/second), and is a measure of positive charge flowing through a circuit, even though positive charges stay stationary in a conductor (weird!). Resistance (measured in ohms) is additive, that is, if you add resistors to a circuit in series, their resistance is added. Amperage is equivalent to volts per ohm."

"A battery uses a chemical reaction to release electric potential energy for charges, creating voltage, and different chemical reactions results different amounts of voltage being created (hence the different kind of batteries). Ohm's law relates current, voltage and resistance I = ∆V/R. Resistors use up voltage as current flows through them."

"Ohm's law can be applied to a basic circuit to determine how much current will flow in it, given the total amount of voltage from ideal batteries, and the equivalent resistance of all the resistors."

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.
"Nothing too confusing. The convention of the positive charges moving is a little weird though."

"I understand most of the reading but would like to hear about short circuits. Also would like to some more examples based on this reading assignment."

"I found the application of the concepts to the examples confusing, but I did not find the concepts to be confusing."

"I'm a little confused as to how I am suppose to use Ohm's law--it does seem somewhat straight forward but I just need clarification."

"I'm not too sure what resistance is? How do I find out the resistance of something?"

"I am a little confused on the way 'stacking' works with batteries."

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. ** [2] more; less. ******** [8] more; more. **************************** [28] (Unsure/guessing/lost/help!) ** [2]

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. * [1] less; more. ******************************* [31] more; less. ******** [8] more; more. [0] (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. * [1] low; high. ********************************* [33] high; low. ***** [5] high; high. * [1] (Unsure/guessing/lost/help!) [0]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Why does a good insulator have a high resistance? What is an example of an insulator?" (A conductor is a material where electrons can flow freely from atom to atom, typically copper, aluminum, or even gold is used in circuit wiring. An insulator is a material where the electrons cannot move from atom to atom, and since they are "pinned" to each atom, no (or very little) current is able to flow through an insulator, such as rubber, plastic, or ceramic, which are used to safely enclose circuit wiring.)

"When 'stringing' together several resistors in series, is the current equal throughout the line or does it get progressively weaker as it goes through multiple resistors?" (Since the electrons continuously travel around a complete circuit (in the opposite direction from "conventional" current), the electrons don't get used up, so the current has to remain the same through all the resistors. What does get "used up" through each resistor is the potential (which reflects the electric potential energy that gets "used up" to push electrons through the resistors.)

"This is probably what I'm looking forward to most out of this semester. Unless you think there is something cooler?" (Feynman diagrams. #justsaying)

"I meant to do this assignment earlier, but I ended up taking a nap instead. I blame my cat." (I have two cats. So I take a lot of naps.)