## 20160410

### Online reading assignment: magnets, magnetism, and magnetic forces from fields

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

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.
"There are two types of poles, north and south. They create B fields which are vectors following the flow of the field which is found by using test magnets."

"Magnetic field lines travel in closed loops. Both on the outside of the magnet and the inside."

"Basically an extension of what we've already known about electric fields (which is not the same as a magnetic fields; they're two parts of a whole). North magnetic poles create outward facing magnetic fields, and south magnetic poles create inward facing magnetic fields, so the overall result is a circular magnetic field loop."

"You label two magnets exerting force on each other a source and a test pole. If the source and the test are facing the same direction the magnets will repel. If they are facing opposite directions than they will attract. "

"In a direct model we are focusing on a source magnet exerting force on a test magnet, and depending on the position of the ends of the magnets there can be an attraction or repulsion. In field model, a magnet creates a field, which exerts the force on a test magnet. Closed loops are formed with the magnetic field flowing N to S."

"The only thing I understood was the right hand rules; how to distinguish between the 'Crouching Tiger' and the 'Hidden Dragon' which was a good way to help me remember the difference between the two."

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 a little confused on how to use the field models. I just do not understand how I would use them in a situation. I also don't understand the right hand rule. I'm excited to find out how to do the right hand rule when we have our fingers labeled in class tomorrow."

"'Hidden Dragon' and 'Crouching Tiger.' I don't get them. Please demonstrate them during lecture."

"How does the right-hand rule helps us out when describing magnetic fields? I guess I just need it explained to me in class but I just do not understand how the right hand rule explains the direction of where the magnetic force is exerted."

"Most of it."

"I think I'm good?"

Outside of a bar magnet, magnetic field lines travel from the __________ pole to the __________ pole.
 north; south. ******************************** [32] south; north. ** [2] (Unsure/guessing/lost/help!) [0]

Inside of a bar magnet, magnetic field lines travel from the __________ pole to the __________ pole.
 north; south. ******* [7] south; north. ************************ [24] (Unsure/guessing/lost/help!) *** [3]

State the symbol used for the magnetic field, and the SI units for magnetic field strength.
"B, and the units are teslas."

"B, newtons."

"M."

When properly using right-hand rule 1, in general there can be any angle between the v thumb and B finger (depending on the situation). In general, specify the angles between the other fingers used in right-hand rule 1.
(Only correct responses shown.)
B finger and F finger: exactly 90° only [42%]
v finger and F finger: exactly 90° only [42%]

In general, the direction of the force of a magnetic field on a moving charged particle will be along the:
 particle's velocity vector. ***** [5] the magnetic field line. ************** [14] (Neither of the above choices.) ****** [6] (Unsure/guessing/lost/help!) ********* [9]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I can't seem to get my brain back into school mode. I think hearing a lecture and seeing some examples of everything will help."

"Still pissy that everything is based on the direction of positive charge movement. I guess it works if you don't think about it."

"Yeah I just do not understand the right hand rule P-dog, help a physics gangsta out."

"How in the heck does anyone understand what's going on right now..."

"What the heck is up with these hand signals!?"

"Hidden Dragon. Crouching Tiger. Hidden Dragon. Crouching Tiger." (Hungry Dragon. Crunchy Tiger.) "