20130407

Online reading assignment: magnetism

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 magnetism concepts.

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.
"That Earth's magnetic north pole is south, and that magnetic bacteria are cool."

"I am really confused on magnetism, and therefore didn't find anything interesting."

"The compasses and the way they reacted to the bar magnet."

"I thought that it was very interesting that they have never found a magnetic monopole and how crazy weird and cool it would be to do that research."

"Magnets are interesting--I've always been fascinated with how they work. They are also fun to play with."

"I found it interesting that magnets have inside and outside magnetic field lines. I thought that magnetic only had field on the outside not the inside."

"There have been theoretical predictions of the existence of the magnetic monopoles, but years of experiments have yet to turn up a single one. I seem to like learning about the things we don't know in the universe more than the things we know."
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"The source of magnetism was not detailed. What makes an item in nature magnetic?"

"Everything was confusing, I don't really understand the two-step model, and how the B field comes into play."

"Whats really going on in a magnet? How come you can cut it in half and still have both poles? Is it made of the same medium? Can you reverse the poles?"

"Keeping track of what each letter and symbol stands for."

"I am confused about B force lines and could use some clarification."

"Why is it that magnetic monopoles can't exist or if they do are very rare? If one does exist what would be an example of one?"

"I would benefit from going over the field models. I don't understand what you mean by 'source' and 'sink.'"

"I found it confusing to understand why a magnetic monopole can violate the closed loop rule in a magnetic field. I couldn't wrap my head around the idea of the rule being violated."

"The magnetic field vector at any point is tangent to the field line and the magnitude of the dield is proportional to the number lo lines per unit area perpendicular to the lines."
Explain why a magnetic monopole would violate the rule that "magnetic field lines are always closed loops."
"A magnetic monopole does not exist because the magnetic field is created between two poles and does not exist with one north or one south pole, they must be interacting. Therefore, if a monopole existed, it would not create a loop but simply send out a north or south pole magnetism."

"A monopole would have an open loop because it only has one pole, not two. You cant just cut a bar magnet in half and have two monopole magnets."

"If there is a monopole, there is no opposite pole to close the loop. Therefore there is no pole and even dipoles that are split become two dipoles. As described in the text, if monopoles do exist they are extremely rare in this universe."

"There would be no place for the field lines to begin or end."

"If there are no magnetic monopoles there is no place for the field lines to begin or end, so they must be close loops."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Which way does the magnetic field travel within a bar magnet? I just assumed it would complete a loop and go back to the north from the south." (Yes.)

"Can you explain monopoles more thoroughly? Thanks!" (First, let me know when you find one.)

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