## 20160328

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 Req 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.)