Online reading assignment: advanced electricity (review)

Physics 205B, spring semester 2019
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 re-reading textbook chapters and reviewing presentations on advanced electricity concepts.


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.

"How to calculate equivalent resistance for parallel circuits and series."

"In series resistors will add up to attain the resistor equivalent and that resistors in parallel will be the inverse of the resistance added together and then inversed again."

"Why an ammeter has to have a resistance of zero, because it measures current and if it had a resistance it would interfere in that."

"Since we had lab, I have a much better understanding of how voltmeters and ammeters work and why they need to have the resistance they have. Since ammeters are measuring the current through a circuit, they need to have a very very low resistance so they don't disturb the circuit they are measuring. The voltmeter measures the voltage difference for a resistor like a bulb. They have to have a very high resistance so they don't create a short in the circuit."

"When the amount of resistors in parallel goes up the resistance gets dangerously low and this causes current to get very high at which point it can become dangerous because its heat can melt the material used to insulate wires, thus exposing wires to other surrounding surfaces and possibly sparking a fire if they come in contact with each other."

"Grounding is an important aspect of safety when it comes to electrical appliances such as clothes dryers. A three-pronged plug connects the metal casing of a dryer to a copper pipe in the ground so that if wiring becomes lose inside the dryer and touches the casing, a person who is also touching the casing will not be shocked. This is because the copper pipe would have much less resistance than the person's body."

"I understand the relationship between resistance and current in series and parallel circuits a lot better after reviewing for this quiz. I understand the measurements that ammeters and voltmeters make better after reviewing the presentation."

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'm still a little confused on the junction and loop rules."

"I'm still a little confused on why ammeters need to have a low resistance wile voltmeters want to have a high resistance. I'm also confused on the measurement process on a voltmeter."

"I do not quite understand joule heating."

"I'm still confused about power and how the amount of power used varies for resistors with different magnitudes in series or parallel circuit."

"I couldn't quite grasp the idea of the power dissipation. I guess I don't know what to use it for or how to use it..."

State the unit of electrical power, and give an equivalent definition in terms of other SI units.

"Watts, amps times volts."

"Watts, which is joules per second."

What are the resistances of these (ideal) devices?
(Only correct responses shown.)

Ideal light bulb: some finite value between 0 and ∞ [65%]
Burnt-out light bulb: ∞ [35%]
Ideal wire: 0 [58%]
Ideal (non-dead) battery: 0 [42%]
Real (non-dead) battery: some finite value between 0 and ∞ [61%]
Ideal switch, when open: ∞ [36%]
Ideal switch, when closed: 0 [42%]

Two light bulbs with different resistances r and R, where r < R, are connected in series with each other to an ideal emf source. Select the light bulb with the greater quantity.
(Only correct responses shown.)

More current flowing through it: (there is a tie) [46%]
Larger potential potential difference: light bulb R [45%]
More power used: light bulb R [52%]

Two light bulbs with different resistances r and R, where r < R, are connected in parallel with each other to an ideal emf source. Select the light bulb with the greater quantity.
(Only correct responses shown.)

More current flowing through it: light bulb r [55%]
Larger potential potential difference: (there is a tie) [23%]
More power used: light bulb r [36%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"Starting a fire from bubble gum wrapper was very interesting. I love it when the concepts we are learning are applied to survival skills."

"No questions today just hope class will clarify my confusion."

"I think you didn't post the blog that pertains to this reading assignment?" (Actually the presentations for this assignment were for review; and these are more advanced questions that build on top of what you've already seen in class and from the textbook, as opposed to being directly off of the presentation slides.)

"I like to get more examples about resistances problems like this in class and get to do a hands on problems."

"How does the internal resistance differ for an ideal versus real battery?" (Ideal batteries have zero internal resistance, they purely provide an emf (potential difference, voltage) without any other complications. A real battery does have an internal resistance, as the chemical reactions that release energy to produce its emf (voltage) also produce inert waste products that still sit inside the battery to impede current. A fresh new battery will have very little internal resistance (very little waste products), and an old battery will have some internal resistance (more waste products), while a dead battery will have a very high internal resistance (nearly all of it inside is waste products). You'll get to investigate this in a later lab.)

"You need to 'make it rain' more in terms of extra credit. You must increase the extra credit limit! This is because, among other things, the actual quizzes do not accurately reflect what is taught."

Online reading assignment: advanced electricity

Physics 205B, spring semester 2019
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 reviewing presentations on circuit analysis and previewing presentations on advanced electricity concepts.


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.

"An ammeter must have a resistance that is ideally 0 while a voltmeter must have a resistance that is ideally infinity. Joule heating is when the power used by the circuit's resistance due to the about of current flowing through it."

"Power measures the rate of electric potential energy usage. It can be calculated as current squared times resistance or current times potential. When resistors are connected in parallel, resistance decreases and current increases. This increase in current can overload the circuit."

"Voltmeters measure the amount of electrical potential used by an element in the circuit and ammeters measure the amount of current passing through an element of a circuit."

"Ammeters measure the current of any circuit element that is "broken" open by measuring the current after it travels through the element. The ideal resistance of an ammeter is zero. Voltmeters measure the amount of electric potential used by any circuit potential, and measures the current of both before and after the element. The ideal resistance of a voltmeter is infinite."

"Series wiring is when devices are connected so that the same current runs through both devices. Parallel wiring is when devices are connected so that the same voltage is applied across each device. The junction and loop rules set the parameters through which current and voltage can move through a circuit."

"If there is too much current going through something, that something will heat up and it can become dangerous and lead to a runaway current which can cause fires and other damages. I also understand how series resistors and parallel resistors divide/use the current in a circuit. Whatever potential a battery adds to a circuit, the resistors will use up the same amount. Circuit breakers are designed to trip a current before it becomes dangerously high turns to a runaway current."

"That runaway currents can be prevented by circuit breaker that interrupts the current if it becomes to high due to excessive appliances being plugged into the same outlet. Each appliance plugged in is considered a resistor, so when many appliances are plugged into the same outlet the resistance becomes dangerously low and the current becomes dangerously high. Outlet overload if dangerous because it causes the wires to heat up thus melting the outer coating that insulates the current flowing through the wire. When the coating is melted off it can make contact with other surfaces and create a spark which could cause a fire."

"Honestly not a lot. Parallel circuits and resistors. Circuit breakers."

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'm going to need more help plugging in the numbers for the different equations."

"The equations may need more examples. Need extra practice on equations."

"I understood junction rule but could use another run through on it. Just in case."

"Can you describe more about the concept of parallel resistors?"

"The section on circuits wired in series and parallel. I am still trying to understand where one starts, the series or parallel."

"I do not really understand how a voltmeter makes measurements. I understand the equations involving power, but am unsure of how to apply the equations. I think it will make sense after practicing with lots of examples."

"I do not really understand why ammeters need to have a low resistance and voltmeters want to have a high resistance. Also (this might be from what we covered earlier) I do not understand why the resistance will decrease when multiple things are plugged into a circuit. This applies to my house because it happens fairly often and my circuit breaker stops the current."

"I am not sure why the resistance for an ideal ammeter is equal to zero while the resistance of and ideal voltmeter should be very high."

"I think I am kinda fuzzy on some of the terminology and how each of the aspects are used. I get the basic concepts of what is going on in each part of the presentation, but if I have to describe it using the right terminology, I am pretty lost."

"Not too confused after this chapter."

"It wasn't too confusing, but I need to read through it once more to get the concept a bit better."

"All pretty good I think! Maybe?"

What are the resistances of these (ideal) devices?
(Only correct responses shown.)

Ideal ammeter: 0 [75%]
Ideal voltmeter: ∞ [69%]

Determine what will happen to the following parameters when additional electrical appliances are plugged in and turned on in the same household circuit.
(Only correct responses shown.)

Equivalent resistance R_eq of circuit: decreases [78%]
Current I flowing through emf source: increases [56%]

A fuse or circuit breaker is designed to prevent too much __________ in household wiring.

current.	********************** [22]
voltage.	*** [3]
(Both of the above choices.)	****** [6]
(Neither of the above choices.)	[0]
(Unsure/guessing/lost/help!)	* [1]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"This subject can be shocking."

"I really liked the 'Twinkle, twinkle, little star, Power equals I-squared R' nursery rhyme. I'll definitely remember this."

"This was a super-interesting lecture because my house burnt down and there were suspicions that it was because of a faulty circuit breaker! So now I understand how that could be majorly bad. I wonder how likely that is?"

"I guess the electrons could just be looked at as the current (or the amount of electrons flowing through a circuit is equal to the current)?" (Yes, but remember that the direction of current is actually the reverse of the actual direction of electrons, due to the arbitrary assignment of negative charge to electrons.)

"Why should a voltmeter have an ideal resistance of infinity?" (When current flows through a resistor, the current doesn't get "used up" (the same amount that goes in comes back out), but the potential/voltage/energy per charge gets "used up." So a voltmeter that measures how much voltage gets "used up" by a resistor is attached on either side of the resistor to compare how much voltage there is in the current before entering the resistor, to how much voltage there is in the current after exiting the resistor. You don't want current to actually flow through the voltmeter when taking these measurements (as you don't want it to affect the current flowing through the resistor that it's measuring), so it should ideally have a resistance of infinity in order to "block" current flowing through itself.)

"What is more dangerous volts/voltage or current? Are they the same?" (As for which is more dangerous, current is the actual (backwards) flow of electrons, and too much of that going through your body is bad. Voltage by itself is just the measure of how much energy per charge there is that current could potentially use to flow through you. A very crude analogy is that a bowling ball dropped on your foot is bad. A lot of bowling balls continuously dropped on your foot is very bad. (This is analogous to the amount of current.) Whether a bowling ball starts from an inch above your foot, or from up on a very high shelf above you is a measure of how much potential energy there is should it drop. (This is analogous to the amount of voltage.) So lots of current with a high voltage is dangerous, but high voltage by itself (with no current) is not dangerous, as long as you don't touch anything that would conduct current through yourself.)

Online reading assignment: advanced electricity (review)

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 re-reading textbook chapters and reviewing presentations on advanced electricity concepts.


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 review of Kirckhoff's laws and how to apply them to various levels of complicated circuits. I also sort of understand ammeters."

"The equation for series and parallel, and the addition rules for them are pretty simple, especially after the lab."

"That series resistors are chain like and parallel resistors are when the current can divide up in a fork kind of way and portions of it can pass through two resistors simultaneously. I also understand the equations that come with these concepts."

"An effective voltmeter 'feels' the current without taking anything from it. We are reported the difference between the high and low potentials."

"According to the loop rule, the total change in rises equals the total change of drops."

"When measuring the amount of electrical potential used by a light bulb (or any other circuit element), the digital multimeter must be connected to both before and the current flows through the light bulb. This means that the wiring in the circuit is not modified in order to connect the digital multimeter to measure electric potential (making it an voltmeter), as it 'feels' the amount of electric potential before and after the light bulb, and reports the difference (whether a drop or rise)."

"The difference between an anameter and a voltmeter and how you need to wire them into a circuit to get the readings you want. I also understand the power equation given in the presentation and how you can substitute in Ohm's law and get different variations."

"Ammeters measure the amount of resistance in an item on a circuit like bulb or resistor and has a resistance of zero while voltmeters need a before and after and have a resistance of infinity."

"The circuit analysis presentation, especially after the review in class. The equivalent resistances for series and parallel circuits especially make sense to me: for series, you can simply add the resistances together since the current will only be able to take one path whereas with parallel circuits you have to add the inverses (and take the inverse of that amount) since the circuits have different junctions to go through."

"Joule heating is the rate of energy used per time. Joules per second is equivalent of watts. Ammeters must have resistance ideally zero. Voltmeter resistance ideally should be infinity."

"The power of a circuit is the product of the current and the voltage of that circuit."

"When a circuit is grounded, charge can flow through back to the circuit itself, where it can be released into the ground instead of running through a person's body. Household circuits are wired to have outlets in parallel, meaning that it's important not to overload them as the resistance could become too low."

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 was not sure where we were supposed to find the resistances of the list of devices below so I guessed."

"I would like an introduction on voltmeters. I think they are more confusing than ammeters."

"I don't understand the equations for the potential drops and rises."

"I am finding Kirchhoff's rules (especially the loop one) really confusing. In addition, I'm still not quite sure about voltmeters and ammeters. I don't know some examples using one or both of the ideas would I think help me better understand these ideas."

"I am still confused with the loop rule and would like more of an explanation on it in class."

"I found the section about runaway current and circuit breakers to be confusing. Also I would like to know how the resistance of a voltmeter is infinite."

"I have not read enough of the chapter to determine what I find confusing. At the moment almost all of it is confusing."

"Pretty chill lesson."

State the unit of electrical power, and give an equivalent definition in terms of other SI units.

"Watts, joules."

"Watt, one joule per second."

"Electric power is measured in watts, which equates to Joules per second when using other SI units to define watts."

"Watt (W), also amps times volts."

What are the resistances of these (ideal) devices?
(Only correct responses shown.)

Ideal light bulb: some finite value between 0 and ∞ [71%]
Burnt-out light bulb: ∞ [54%]
Ideal wire: 0 [58%]
Ideal (non-dead) battery: 0 [71%]
Real (non-dead) battery: some finite value between 0 and ∞ [63%]
Ideal switch, when open: ∞ [33%]
Ideal switch, when closed: 0 [29%]

Two light bulbs with different resistances r and R, where r < R, are connected in series with each other to an ideal emf source. Select the light bulb with the greater quantity.
(Only correct responses shown.)

More current flowing through it: (there is a tie) [58%]
Larger potential potential difference: light bulb R [46%]
More power used: light bulb R [75%]

Two light bulbs with different resistances r and R, where r < R, are connected in parallel with each other to an ideal emf source. Select the light bulb with the greater quantity.
(Only correct responses shown.)

More current flowing through it: light bulb r [46%]
Larger potential potential difference: (there is a tie) [38%]
More power used: light bulb r [46%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"It will be better after spring break...hopefully!"

"Can we talk about Kirchhoff's loop rule, and power? I feel kind of lost."

"The potential drop is still not clear to me, reading isn't helping me understand it either." ("Potential" is just another term for voltage, so "potential drop" is the change in voltage ∆V, which measures how much voltage a resistor uses up while current is passing through it. If a Christmas light bulb is connected to an ideal 1.5 V emf, the emf provides 1.5 V to the current passing through it, and then the current as it passes through the light bulb uses up 1.5 V.)

"I didn't understand the upstream/downstream example. Will we be given a path direction and use that to check our answer? Or do we use our answer to determine the direction the current is traveling?" (For very complicated circuits it will not be apparent what direction(s) the current has, but for the scope of this course the direction(s) of current will be given, or will be apparent if you inspect the polarity (the +/− ends) of the emfs on the circuit.)

"Please explain examples above."

"Could you explain the last two examples in class? I'm confused on them (and I hope I'm not the only one)."

"I still don't understand resistors in series and the electric potential difference. How can something with a higher resistance have a lower potential difference than something with a lower resistance?" (Actually, that's impossible (at least for either of the two examples above):

1. For the two light bulbs in series, the same current I passes through them (from the junction rule where there is no junction). Using Ohm's law for each light bulb, ∆V = I⋅R and ∆V = I⋅r, since I is the same for both bulbs, the higher resistance bulb must have the higher potential drop (since it has a higher resistance, it "costs more" in voltage to pass through it).
2. For the two light bulbs in parallel, both light bulbs have the same ∆V potential drop (from the loop rule, as whatever loop you take, each light bulb is supplied directly from the same emf). Using Ohm's law for each light bulb, ∆V = I⋅R and ∆V = I⋅r, since ∆V is the same for both bulbs, the higher resistance bulb will have less current flowing through it, and the lower resistance bulb will have more current flowing through it).)

Online reading assignment: advanced electricity

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 reviewing presentations on circuit analysis and previewing presentations on advanced electricity concepts.


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.

"Learned about voltmeters and ammeters."

"I learned more in-depth the differences between a series wiring and a parallel wiring. Series wiring is when the same electric current runs throughout all the devices. While a parallel wiring is when the same voltage difference is applied to all the devices."

"When measuring the current passing through a light bulb (or any other circuit element), the current that passes through the light bulb must also pass through the digital multimeter. This means that the wiring in the circuit must be 'broken' open to connect the digital multimeter to measure current (making it an ammeter)."

"An ammeter needs a resistance of zero or nearly zero to measure current. While a voltmeter needs a resistance that is nearly infinity to measure the difference in electrical potential."

"A voltmeter is used to measure (delta) V in devices and instruments. The wiring is altered to allow flow through the voltmeter and an instrument such as a light bulb."

"An ammeter has an ideal resistance of zero and is used to measure the current going through a light bulb. A voltmeter measures the electrical potential energy used by a light bulb and has a ideal resistance of infinity."

"'Twinkle twinkle little star, quals I-squared r.' Circuit breakers are designed to prevent runaway circuits from causing damage."

"That with more resistors are added in parallel to a circuit the equivalent resistance decreases. This can result in a very large runaway current."

"Joule heating is the rate of power used per time. As more appliances are plugged in overall resistance decreases in the house which can lead to a dangerous runaway current."

"Joule heating is the term for the rate of energy used per time used by a circuit element of resistance due to the amount of current I flowing through it. For each charge q that uses a certain amount ∆V of electric potential, the amount of electric potential energy used is ∆EPE = q·∆V."

"When more devices are connected to a voltage source in parallel, the resistance decreases and the current increases. This can be a safety issue in household wiring, which is somewhat mitigated by circuit breakers that cut off electricity when the current gets too high. An ammeter measures current, while a voltmeter measures voltage."

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.

"Kirchhoff's loop rule."

"Distinguishing between the resistance of ammeter and voltmeters."

"How an ammeter works. I'm not sure why it should have such a low resistance while a voltmeter should have high resistance."

"What the difference is between ammeters and voltmeters. I mean why does ammeter have a resistance close to zero and why does a voltmeter have a resistance close to infinity. Also in what situations would I use a voltmeter over an ammeter (or vice versa)?"

"Voltmeters and anmeters. Review on how these work and how they are different would be great."

"I am struggling with the parts about the voltmeter and ammeter and their specific uses."

"I do not know what an ammeter is. I do not know the physics behind electrical units."

"How power dissipation fits into everything."

"Clarification on why more resistors will cause an outlet to become 'overloaded'. Why does low resistance cause the wires connected to the outlet to heat up?"

"Runaway current."

"I'm still not exactly sure how a circuit breaker works/how it prevents too much current."

"Power dissipation."

"How the power dissipation equation is constructed, but I need to see more examples of when and what context we use it. Also, how do circuit breakers work? I don't think I understand that."

"I did not find too much confusing. Just heavy information-wise, and a lot to understand."

"I have not found anything confusing."

What are the resistances of these (ideal) devices?
(Only correct responses shown.)

Ideal ammeter: 0 [78%]
Ideal voltmeter: ∞ [69%]

Determine what will happen to the following parameters when additional electrical appliances are plugged in and turned on in the same household circuit.
(Only correct responses shown.)

Equivalent resistance R_eq of circuit: decreases [63%]
Current I flowing through emf source: increases [65%]

A fuse or circuit breaker is designed to prevent too much __________ in household wiring.

current.	********************** [22]
voltage.	******* [7]
(Both of the above choices.)	** [2]
(Neither of the above choices.)	[0]
(Unsure/guessing/lost/help!)	* [1]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"Can we go over a brief overview of electricity I forgot a lot of the material? That's on me, but a review would be nice."

"Please go over the examples above thanks!"

"Not too many questions, except for the ammeter vs. voltmeter parameters mentioned above."

"How are electrical fires an issue if circuit breakers are meant to cut off the power when too much current is passed through it?" (Ideally the circuit breakers will always do their job, but some people might try to prevent the circuit breaker from tripping in order to keep their appliance working, and/or there may be a connection or wire that is faulty or rated less than what the circuit breaker will allow up to, and that part of the circuit will still spark or heat up and catch on fire. So circuit breakers won't prevent every kind of electrical fire hazard.)

"I learned that many videos shown in class shouldn't be attempted at home."

"This second part of semester with quizzes almost every week is kinda scary to me." (It's scary to me, too. So be sure to enjoy your spring break before coming back to the grind.)

Physics quiz question: USB-C communication connection wire power dissipation

Physics 205B Quiz 5, spring semester 2017
Cuesta College, San Luis Obispo, CA

The communication connection wire within a Type-C USB cable has a resistance of 5.6 kΩ, and while attached to a smartphone, 80 µA of current passes through this wire. While this current passes through the communication connection wire, the electrical power dissipated within it is:
(A) 1.4⨉10^–8 W.
(B) 3.6⨉10^–5 W.
(C) 0.45 W.
(D) 2.5⨉10³ W.

[*] androidauthority.com/usb-type-c-and-3-1-explained-656552/.

Correct answer (highlight to unhide): (B)

Given the resistance R and the current I that passes through the communication connection wire, the voltage drop across it is given by Ohm's law:

∆V = I·R,

∆V = (80⨉10^–6 A)·(5.6⨉10³ Ω) = 0.448 V.

The power dissipated in the communication connection wire is then:

P = I·∆V,

P = (80⨉10^–6 A)·(0.448 V) = 0.00003584 W,

or to two significant digits, 3.6⨉10^–5 W.

Alternatively, the power can be directly calculated by making a substitution for ∆V using Ohm's law:

P = I·∆V = I·(I·R),

P = I²·R,

P = (80⨉10^–6 A)²·((5.6⨉10³ Ω) = 3.6⨉10^–5 W.

(Response (A) is I/R; response (C) is ∆V = I·R; and response (D) is ∆V·R= I·R².)

Sections 30882, 30883
Exam code: quiz05vLeY
(A) : 6 students
(B) : 17 students
(C) : 0 students
(D) : 3 students

Success level: 65%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.86

Online reading assignment: advanced electricity (review)

Physics 205B, spring semester 2017
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 re-reading textbook chapters and reviewing presentations on advanced electricity concepts.


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.

"Kirchhoff's junction rule states that the sum of all the currents flowing into a system must be equivalent of the the current flowing out, Kirchhoff's loop rule states that there are rises and drops in potential but the net result in a complete loop stays the same. When an ammeter is used to break a circuit it essentially acts as a wire with zero resistance, in contrast a voltemeter has almost infinite resistance and will likely block any current if used to break a circuit."

"Kirchhoff's rules--for the junction rule the sum of all currents flowing into a junction must equal the sum of all the currents flowing out of the same junction. For the loop rule, if there is a complete loop in a circuit, where we end up at the same spot as we did when we started, all of the electric potential rises added together must equal all the electric potential drops added together."

"A change in electric potential represents the potential energy used by a charge. For each charge that uses a certain amount of electric potential, the amount of electric potential energy used is equal to charge times electric potential."

"Resistance increases in series circuits and decreases in parallel. Voltmeters measure potential and have high resistance, Ammeters measure current and have negligible resistance."

"I now understand how a voltmeter takes its reading of the change in voltage across a circuit by connecting in parallel to the system. Finding the current of the circuit and multiplying by each of the resistors between the connections of the voltmeter show the appropriate reading."

"As resistance goes down in a shorted battery circuit, there is more danger associated. For example, the gum wrapper being set on fire as it completed the circuit. Had the gum wrapper had a higher R value, there would be less risk of fire."

"Nothing, honestly."

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.

"Not much, just need to do a few more circuit-solving problems."

"When you have to redraw the circuits because of parallel or not parallel. I just need to practice redrawing them."

"I think I need to see more examples of how to use the equations when using either an ammeter or a voltmeter."

"The different types of switches than can either be open or closed and the effect that has on resistance."

"The stuff that we covered on Monday in class with the voltmeter and ammeter stuff. I feel like there isn't enough understanding of the concept to go off of when we did the worksheet. So the worksheet was more so guessing my way through it than really understanding things. I left class with a bunch of question marks in my head."

"Using given equations to make substitutions for power dissipation."

"The power equations. I do not know how power can be expressed three different ways."

"A lot of stuff, as usual."

What are the resistances of these (ideal) devices?
(Only correct responses shown.)

Ideal light bulb: some finite value between 0 and ∞ [67%]
Burnt-out light bulb: ∞ [48%]
Ideal wire: 0 [52%]
Ideal (non-dead) battery: 0 [38%]
Real (non-dead) battery: some finite value between 0 and ∞ [76%]
Ideal switch, when open: ∞ [24%]
Ideal switch, when closed: 0 [33%]

Two light bulbs with different resistances r and R, where r < R, are connected in series with each other to an ideal emf source. Select the light bulb with the greater quantity.
(Only correct responses shown.)

More current flowing through it: (there is a tie) [14%]
Larger potential potential difference: light bulb R [52%]
More power used: light bulb R [57%]

Two light bulbs with different resistances r and R, where r < R, are connected in parallel with each other to an ideal emf source. Select the light bulb with the greater quantity.
(Only correct responses shown.)

More current flowing through it: light bulb r [57%]
Larger potential potential difference: (there is a tie) [38%]
More power used: light bulb r [38%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"Could we go over power dissipation examples?"

"Doing Monday's lab really helped me distinguish the difference between an ammeter and a voltmeter and what each one measures."

"What makes the resistivity of materials strongly dependent on temperature?" (Since current is the flow of electrons, there are two things that either help or do not help these electrons move. The speed of these electrons depends on the temperature--cold temperatures mean that they can move slowly, and hot temperatures mean that they can move quickly, so raising the temperature tends to increase the speed of electrons and decrease the resistivity of the material. However, electrons need to pass through all the atoms in the material, and the vibrational motion of these stationary atoms also depends on the temperature--cold temperatures mean that they randomly vibrate very little, and hot temperatures mean that they randomly vibrate a lot, so raising the temperature tends to increase the random vibrations of the atoms, which can "block" to motion of electrons, and increase the resistivity of the material. These are two competing effects, and for different materials one effect will typically dominate over the other, and even this might change at different temperature ranges for the same material.)

"I don't understand how adding plugs will become dangerous when the ideal wires have low resistance." (If you start to add more resistors in parallel, the equivalent resistance will begin to decrease. E.g., five 100 Ω resistors in parallel have an equivalent resistance of 20 Ω, ten Ω resistors in parallel have an equivalent resistance of 10 Ω. Since all the outlets in a single household circuit are wired in parallel, plugging in more appliances (with a given resistance) means more are connected in parallel with each other; and then the equivalent resistance goes down, and the amount of current that will flow through the wire supplying that part of the house will increase. Power dissipated in the wire is I²·R, so even if the resistance of the wire is small, the current-squared will be very high, and the wire can get dangerously hot enough to melt its insulation wrapping, and start a fire behind the walls!)

"Why can we disregard the positive versus negative flow when dealing with an ideal battery? "For an emf source (such as an ideal battery) with a potential difference of ε, we do not pay attention to the direction of current flowing through the battery, but instead watch how we move through the battery with respect to the positive (+) and negative (–) terminals, which respectively represent the higher and lower electrical potential ends of the battery." (If this sounds non-physical, it kind of is--this is done when applying the loop rule (looking for potential drops and rises), so "walking around" a loop may or may not correspond to the actual flow direction of current. When applying the loop rule, if you travel into the (–) terminal and out of the (+) terminal of a battery, then you increase in potential (this is the conventional way a battery would be placed in a circuit); but if you happen to travel into the (+) terminal and out of the (–) terminal of a battery (which means that it is put in "backwards"), then you decrease in potential.)

"Brooo, it's April already." (We're still in March. #toosoon)

Online reading assignment: advanced electricity

Physics 205B, spring semester 2017
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 reviewing presentations on circuit analysis and previewing presentations on advanced electricity concepts.


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.

"When measuring the amount of electrical potential used by a light bulb (or any other circuit element), the digital multimeter must be connected to both before and after where the current flows through the light bulb. This means that the wiring in the circuit is not modified in order to connect the digital multimeter to measure electric potential (making it an voltmeter), as it 'feels' the amount of electric potential before and after the light bulb, and reports the difference (whether a drop or rise)."

"The more appliances that are plugged in an outlet, the resistance will decrease This can be very dangerous. Circuit breakers are to prevent current levels from reaching a dangerously high level--if the circuit breaker is triggered, this turns off the electricity so that the wires in the house do not become a danger to one's household."

"All household electrical outlets provide 120 volts of electric potential and operate independently of each other. The outlets are wired in parallel to each other to the same 120 volt electromotive source."

"An ideal ammeter has zero resistance because it measures the current within a circuit. Resistance in the ammeter is added to the circuit, which causes a reduction in current (since it is added in series). This would result in an artificially low measurement of current within a circuit."

"Right now this makes sense, currents are measured with anmeters and it tells you how much is running though the circuit. Voltmeters are used to measure the change in EPE of the item that you are using."

"A voltmeter measures the amount of volts running through a circuit. It should be hooked up to the first part of the circuit and the last part of the circuit so that it can read the change in potential when the voltage goes through the light bulb or resistor. There should be a really good resistor in there so that all the voltage is used up as it goes back to the start of the circuit. An ammeter measures current that passes through a light bulb. Since the current must pass through the digital multimeter the wiring of the circuit must be opened up so that the ammeter can read the current going through the circuit. There should be no resistance in the ammeter because you want to measure the original amount of current running through it."

"I learned that ammeter measures current and must be 'broken into' the circuit in order for the current to flow through it and a voltmeter measures the voltage and does not need to be 'broken in' since it measures a potential differences. The resistance for a voltmeter is infinite to avoid any current going into the voltmeter where as with the ammeter, the current is zero to allow the current to flow freely."

"In this homework assignment, it explains how multimeters must be used correctly to measure accurately because they are breaking a circuit when used as an ammeter. When used as a voltmeter, a multimeter must be connected to both before and after the current flow through a light bulb."

"I love all of your mnemonics! That is the best way for me to remember things so it makes less work for me to have t come up with little rhymes! "Twinkle, twinkle, little star, Power equals I squared R."

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.

"What I found confusing a from this reading assignment was the many different equations. I believe I understood that the different terms are able to be substituted to be able to relate to some of the other equations. When applying the equations was confusing."

"What I found a little confusing was the difference between a voltmeter and an ammeter. I'm still not entirely sure what the difference is except that an ideal voltmeter should have a high resistance and the ideal ammeter should have almost no resistance."

"I don't think I could figure out which equations to use."

"I don't understand how P can equal change in ∆V²/R or I² times R."

"I'd like some more explanation on how multimeters measurements as ammeters and voltmeters differ. Also, how they relate to the equations."

"Nothing was confusing in the reading/lecture material. It was all pretty straightforward."

What are the resistances of these (ideal) devices?
(Only correct responses shown.)

Ideal ammeter: 0 [92%]
Ideal voltmeter: ∞ [80%]

State the unit of electrical power, and give an equivalent definition in terms of other SI units.

"The unit for power is watts (W), or joules (J) per second (s)."

"Not sure."

"Joules = newton·meters?"

"Volts?"

"Coulombs/second or joules/second?"

"Amps?"

Determine what will happen to the following parameters when additional electrical appliances are plugged in and turned on in the same household circuit.
(Only correct responses shown.)

Equivalent resistance R_eq of circuit: decreases [56%]
Current I flowing through emf source: increases [8%]

A fuse or circuit breaker is designed to prevent too much __________ in household wiring.

current.	******************** [20]
voltage.	** [2]
(Both of the above choices.)	** [2]
(Neither of the above choices.)	[0]
(Unsure/guessing/lost/help!)	* [1]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"Why does a circuit breaker trip when you have too many things plugged into outlets at your house?" (In a given room in your house, all the outlets are wired in parallel. Plugging in more appliances (each with a given resistance) means that they are all connected in parallel with each other; each additional appliance plugged in means that the equivalent resistance goes down, and thus the current going through the main wire to that part of the house goes up. A wire carrying a lot of current will tend to heat up, and if it is more current that it is rated for, then there is a fire risk, unless the circuit breaker trips.)

"It is scary to see the damage from a runaway current, that's why I'm not an electrician, haha! Circuit breakers and surge protectors must save a lot of buildings and lives!"

"When the resistance is low, the current is as fast as Usain Volt ; - )" (Well, not necessarily fast (all levels of currents travel at the same speed through a given wire); a better analogy would be that when resistance is low, current is as big as a football offensive line.)

"If power is the rate of electric potential energy (joules) per time, does that make it a second order derivative of electric potential?" (No, electric potential energy is not a derivative of electric potential ∆V, EPE (joules) is merely charge q (coulombs) times ∆V (joules/coulomb). So voltage is a ratio of energy per charge, rather than a "per time" derivative.)

"Why must a voltmeter have a resistance that is ideally infinity? I'm confused on this and what it means to have voltage." (If the voltmeter did not have an infinite resistance, then current would flow through it, and the voltmeter would then be measuring how much voltage is lost by the current flowing through itself, rather than measuring how much voltage is lost by what it is connected to (say, a disconnected battery, or a light bulb that has a given amount of current flowing through it.)

"Two parallel resistors double the resistance whereas two series resistors will halve the resistance." (#wut)

"Spring break!"

Online reading assignment: advanced electricity (review)

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 re-reading textbook chapters and reviewing presentations on advanced electricity concepts.


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.

"Some of it, but it gets confusing. I think I need to look at more specific instances."

"The differences between series and parallel. I just need to review the different equations and such."

"Learning a little more about what makes an ammeter. I found it interesting to read the advanced electricity blog and learn more about every day electricity such as household electricity."

"Ammeters have zero internal resistance, making them dangerous if you wire them into a circuit wrong. The circuit should be 'broken' and the ammeter wired into the gap; connecting it in parallel can cause an unsafe rise in current. Voltmeters can be used to measure the voltage drop/rise across any two points."

"Same good ol' electricity. Don't want too much power going through parallel circuits which is why you have a circuit breaker just in case. [Series] resistance adds up, and you don't want to mess up multimeter readings due to improper placements."

"An ammeter measures current flow and must have zero resistance to not change the circuit it is measuring. A voltmeter simply gives you the pressure difference between any two points and the voltmeter has infinity resistance."

"Placing more resistors lined in-parallel within a circuit will result in a greater chance of accumulating a runaway current. It took me the lab as well as reading to sort of visually see how current can steadily build within a circuit as its resistors are placed in parallel. The spread of current allows for the possibility of there being less potential drop in electric potential energy as current travels through each given resistor in parallel."

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.

" Kirchhoff's rules are a little fuzzy to me but I just have to do some more example problems to fully understand them."

"I still just find resistors and ammeters confusing. Maybe they aren't as complicated and I am making it more complicated than it really is. I just need to go over equations and really get a solid feel for it."

"I'm kind of lost on the application of bulbs and switches, etc."

"Why resistance goes to infinity for a dead battery, or for a burnt-out light bulb."

"I am confused on everything!"

"Nothing particularly."

What are the resistances of these (ideal) devices?
(Only correct responses shown.)

Ideal light bulb: some finite value between 0 and ∞ [65%]
Burnt-out light bulb: ∞ [36%]
Ideal wire: 0 [55%]
Ideal (non-dead) battery: 0 [39%]
Real (non-dead) battery: some finite value between 0 and ∞ [74%]
Ideal switch, when open: ∞ [48%]
Ideal switch, when closed: 0 [48%]

Two light bulbs with different resistances r and R, where r < R, are connected in series with each other to an ideal emf source. Select the light bulb with the greater quantity.
(Only correct responses shown.)

More current flowing through it: (there is a tie) [52%]
Larger potential potential difference: light bulb R [55%]
More power used: light bulb R [29%]

Two light bulbs with different resistances r and R, where r < R, are connected in parallel with each other to an ideal emf source. Select the light bulb with the greater quantity.
(Only correct responses shown.)

More current flowing through it: light bulb r [35%]
Larger potential potential difference: (there is a tie) [35%]
More power used: light bulb r [16%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"I appreciate the fact that you had our midterm right before Easter so that our holiday was free and how you're having our quiz this Friday so that our spring break is free. Thank you!" (Thereby ruining my Easter and my spring break. #yourewelcome.)

"This was really confusing!"

"Twinkle twinkle....dang it!"

"I suck at physics. It's ruining my self-esteem."

"Don't April fools me with the quiz. #notcool"

"How can we determine the resistance of certain [ideal/real/burnt out] devices? I'm not sure how to go about evaluating things." (We'll go over these on the worksheets in class.)

Online reading assignment: advanced electricity

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 reviewing presentations on circuit analysis and previewing presentations on advanced electricity concepts.


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.

"Power is the rate of electrical potential energy used per time. Electrical outlets in a house are wired in parallel so that each appliance you plug in receives the same amount of voltage, but this can also be dangerous because the more appliances you plug in the lower the equivalent resistance becomes. If the resistance gets to low, the increased current can cause damage."

"The proper way to set up the instruments provided to us in lab, and the importance in making sure we connect everything properly. I also understand power dissipation."

"When measuring passing current through a circuit into a bulb the current flowing needs to be broken so it can be measured with a multimeter."

"When measuring the current passing through a light bulb the current that passes through the light bulb must also pass through the digital multimeter,and when measuring electrical potential used by a light bulb, the digital multimeter must be connected to both before and the current flows."

"To measure electric potential, we have to take the measurement before and after the current goes through the source(bulb). To measure currents, the current also has to go through the multimeter. circuit breakers are used to trip when a current is too large, to avoid runaway current from melting the insulated wire and cause a fire."

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.

"The concept of potential drops in the loop rule is a little confusing to me. I also don't know when to use the junction rule."

"I don't understand what power dissipation is or how it is useful. I tried reading in the book ,but I was just really confused."

"There's nothing that I really find confusing."

"I find some of the theories confusing along the way but I know that with more practice I will be able to do better on these types of circuit problems. I am still weak on my vocabulary as well so I need to work on that."

"Why an ammeter has to have a very low resistance and why a voltmeter's resistance should be very large."

What are the resistances of these (ideal) devices?
(Only correct responses shown.)

Ideal ammeter: 0 [69%]
Ideal voltmeter: ∞ [67%]

State the unit of electrical power, and give an equivalent definition in terms of other SI units.

"Watts, or joules per second."

"Volts."

"Amps."

"Unsure."

"Watts or amps? I'm not quite sure."

"Electric power is P = I·∆V, and the units for this equation is the watt, or one joule per second."

Determine what will happen to the following parameters when additional electrical appliances are plugged in and turned on in the same household circuit.
(Only correct responses shown.)

Equivalent resistance R_eq of circuit: decreases [54%]
Current I flowing through emf source: increases [52%]

A fuse or circuit breaker is designed to prevent too much __________ in household wiring.

current.	********************** [22]
voltage.	** [2]
(Both of the above choices.)	* [1]
(Neither of the above choices.)	[0]
(Unsure/guessing/lost/help!)	*** [3]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"I want to see what my grade for the midterm was. Super scared!"

"Happy Easter ????"

"Hope the midterms weren't too hard to grade! Meaning that we did well...good job guys!!!"

"I've been studying calculus and biology all weekend. Two tests Thursday. Eat, sleep, pray, calc, pray and do calc in the middle of prayer, bio, repeat."

"Can we please go over the difference between voltage and current again?? I'm still really shaky on that."

"What is the different between amps and volts. is it simply that amps are per second and volts is just the amount of current at a given time?" (Amps is the amount of current, or charges per second, flowing through a wire. Volts is the amount of potential, which measures how much energy each and every (unit) charge carries as they flow through a wire. So essentially, amps is how much "stuff" is flowing through a pipe, while volts is how much "push" is contained in the stuff flowing through a pipe.)

Online reading assignment: advanced electricity (review)

Physics 205B, spring semester 2015
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 re-reading textbook chapters and reviewing presentations on advanced electricity concepts.


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.

"Isn't this the same reading assignment? I understand basically everything except when you were talking about that circuit last time in class."

"A fuse is put in series with the circuit and is designed to melt—due to I2R heating—if the current to the circuit exceeds a given value. The melted fuse is an open switch, interrupting the circuit and stopping the current."

"I understand Kirchhoff's rules a lot better, but I think the labs are really helping me understand all of this cause I feel like electrical stuff really isn't my strong point."

"'Joule heating' is the historical term for the power (or rate of energy used per time) continuously used by a circuit element of resistance R due to the amount of current I flowing through it, as in those radiating coils."

"I understand that ammeters must be wired in series while voltmeters must be set up in parallel. If ammeters are wired in parallel the current will take the path of least resistance (zero for an ideal ammeter) instead of going through the resistor which would result in a dangerous amount of current in the circuit. If a voltmeter is wired in series no current can flow through the circuit due to its infinitely high resistance that would zero out the current. The remaining voltage would be a useless reading."

"'Twinkle twinkle little star, power equals I squared r."

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 had some difficultly understanding the loop rule."

"I found power confusing. Wiring both voltmeters and ammeters seems tricky still."

"I get confused with the difference between voltage and current. I don't understand (yet) how to read or figure out electric potential differences. It felt like in lab you could get different readings depending on where you put the leads, but I'm not sure.'

"The most confusing part of the readings and also apart of the labs is understanding how the ammeters, ohmmeters and voltmeters are used unless they are first explained to me."

"I'm confused by the law for circuits and what it is actually used for and how to manipulate the variables."

"I'm not exactly sure how runaway currents work. Additionally I dont understand how the circuit breaker is implemented to prevent runaway currents."

"I still get confused with electric potential, electrical potential energy, wells and peaks, and the direction of decreasing and increasing values based on the sign of the charge. I also get confused when reducing circuits to find total current and then building them back up again and applying the rules of a circuit in series versus a circuit in parallel. Especially with the more confusing circuit arrangements."

What are the resistances of these (ideal) devices?
(Only correct responses shown.)

Ideal light bulb: some finite value between 0 and ∞ [61%]
Burnt-out light bulb: ∞ [37%]
Ideal wire: 0 [48%]
Ideal (non-dead) battery: 0 [45%]
Real (non-dead) battery: some finite value between 0 and ∞ [61%]
Ideal switch, when open: ∞ [42%]
Ideal switch, when closed: 0 [42%]

Two light bulbs with different resistances r and R, where r < R, are connected in series with each other to an ideal emf source. Select the light bulb with the greater quantity.
(Only correct responses shown.)

More current flowing through it: (there is a tie) [42%]
Larger potential potential difference: light bulb R [45%]
More power used: light bulb R [34%]

Two light bulbs with different resistances r and R, where r < R, are connected in parallel with each other to an ideal emf source. Select the light bulb with the greater quantity.
(Only correct responses shown.)

More current flowing through it: light bulb r [50%]
Larger potential potential difference: (there is a tie) [26%]
More power used: light bulb r [32%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"If I was in prison, I would just study physics all day." (No better way to get pumped up.)

"Will try not to forget this over spring break."

"I think I need an intervention on this conceptual stuff and resistances for real versus ideal devices."

"It all seems simple enough, until it gets confusing."