## 20130414

### Online re-reading assignment: magnetic forces from fields

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 re-reading textbook chapters and reviewing presentations on magnetic forces from fields.

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.
"I found the right-hand rule useful in this presentation because it is very easy to remember as long as you understand it."

"I found the 'Crouching Tiger, Hidden Dragon' right-hand rules very helpful. It makes it very fun to remember the different right hand rules. Thank you."

"How holding a magnet up to a black and white TV will distort the image."

"I think that Shakira doing the right-hand rules is interesting. Maybe she is a secret physicist."

"How a current in wire creates a magnetic field."

"Even though it wasn't on the assigned reading, I read ahead by accident and really found the torque caused by magnetic force pretty interesting."

"It was interesting that 'any' moving charged particle creates a magnetic field, whether it is a magnet or not. How is this? I understand it would create an electric field, but what is magnetic about any particle?"

"The one thing that sticks out to me in this chapter is the first right-hand rule. All I can say is that it is going to be hilarious watching everyone pointing and doing random hand gestures while taking a test."

"I thought that the solenoids were interesting because the can keep a magnetic field nearly uniform. If the loops in the solenoid are close enough then the field lines go straight through one loop and on to the next, all the way down the solenoid."

"I think that it is interesting that a shape we make with our hands relates to magnetic forces."

"This is all pretty amazing. The ability to move something with magnetic forces and not actually touching it is amazing."
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"Even though the right-hand rules are really interesting to me, I still get confused about what fingers go where for various problems!!"

"A big problem with me is that I never know how to ask a question related to the homework or presentation material--it usually gets cleared up during class time."

"I'm not very confident on the hand rules yet. I think I need practice."

"The right-hand rule thing is still kinda confusing to me as I end up pointing fingers in different directions than they should."

"The second right-hand rule for a straight current-carrying wire was confusing, because it was not as well-explained. Does it only show the direction of current and magnetic field, no force?"

"Looking back at the railgun, I guess I don't quite understand why the object is propelled forwards."

"Formulas as always. Some of the terminology has subtle differences in definition and I forget."

"Something that I found confusing were the field models. I just don't understand them with the words. I understand drawings and pictures better than words."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"With two wires next each other, do they repel if the currents go in opposite directions?" (Yes, they will exert repulsive magnetic forces on each other.)

"I'm guessing we aren't going to be building railguns in class?"

"I heard on the radio that SLO Diagnostic Center has the newest MRI machine with the strength of 3 Tesla. What exactly does that mean?" (It means you can start building a railgun outside of class.)

"Can you post a picture of our class doing our hand symbols during the next test?"