## 20130423

### Online reading assignment: flux laws & devices

Physics 205B, spring semester 2013
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 reading textbook chapters and previewing presentations on flux laws and devices.

Selected/edited responses are given below.

Describe something you found interesting from the assigned textbook reading or presentation preview, and explain why this was personally interesting for you.
"It was interesting to read about how transformers work because they are a part of our everyday lives and are important."

"I like how this is kind of a different way to figure out what we just did."

"I thought that the units given from a magnetic field passing through a perpendicular area was Webers. I have a family of friends called the Webers!! I love them!"

"I liked the floating candelabra, although I don't understand it."

"I thought that it was super interesting when the AAA battery lit up the 220 V bulb with a transformer."

"I really liked the idea of magnetic flux and Faraday's Law, they completely made sense to me."
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"Faraday's law was a little hard to follow the way they had it in the textbook."

"When looking at the equations, I still don't quite get what 'Wb' is. Watts?"

"I down quite understand the transformers step-up and step-down business."

"Faraday's law is weird. I think I get it, But what exactly is being induced?"

"I still don't fully understand what happens in transformers or how generators turn magnetic fields passing through areas into emf."

"I honestly tried to read and understand the online presentation and I read the book but I was just lost for a majority of it. I don't feel like I understood much. I would really benefit going over this in class."

"'However, the current induced in a loop (because the external magnetic flux through it is changing over time) will be in the direction that creates a magnetic field that opposes the changes in the external magnetic flux.' I cannot wrap my head around this, I think I just need to see it."

"I think what is difficult has been keeping up with everything so far with magnetic fields and being able to recall fast enough to serve me well with what we are currently working with."
Describe what happens to a wire coil while the magnetic flux through it is changing.
"A coil experiences an induced current when the magnetic field passing through it varies."

"If the magnetic flux is changing then there is an induced emf of the wire coil."

"Heats."
Briefly describe what a transformer is supposed to "transform."
"Voltage up and down as a step-up or step-down transformer."

"A transformer transforms one level of voltage and current into another. A step up transformer raises voltage and lowers current, usually to make long power lines more efficient, and a step down transformer raises current and lowers voltage, usually to make it safe for homes and appliances."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"The levitating chandelier was cool. After further reading the blog post, I was reminded of wireless charging, which I think is induced charging rather than direct charging. This is why the bulbs light up, right?" (Right. You can even buy an aftermarket wireless charging kit.)

"How many cats do you have?" (Right now, only one--and she has her own Facebook page.)