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."
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