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 previewing presentations on magnetic fields of current-carrying wires and loops.
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.
"Magnetic force is attractive if the ends of the source magnet and test magnet face each other with the opposite poles, and repulsive if it ends of the source magnets and test magnet see each other with the same poles. Magnetic field lines are everywhere and the point out from the north end of a source magnet."
"A circle with an × going through it (⊗) is a vector going into the the page ('innie'). A circle with a dot in the center (⊙) is a vector coming out of the page ('outie')."
"What the fingers represent in the first right-hand rule, and how to position them. I also understand that source objects create a magnetic field, which in turn effects a test object."
"I think that I have a pretty good grasp on the basic concepts of magnets and how they interact with each other. After last class, I now understand the first right-hand rule, and I think that I have a slight grasp on the other hand rules, but I know that after we talk about them in class I will fully understand them."
"The first right-hand rule is used to see where the force on the test charge is pointing based on the direction of the B field and the angle of the velocity v. We now see the crouching tiger in its natural habitat."
"I now know how to use the 'Crouching Tiger, Hidden Dragon' right-hand rule signs."
"In the two-step model of magnetism, the source object creates a magnetic B field everywhere around it, and then it's the field that exerts a force on the test object."
"How to use the first right-hand rule in order to find the direction of magnetic field forces. From the other right-hand rules, for a circular loop of wire the fingers curl in the direction of the current and for the straight section of wire the fingers curl in the direction of the magnetic field."
"That RHR2 is used when current is flowing in a straight wire), and models a circular magnetic field around the wire. RHR3 is used when for circular current-carrying wire, and it models the closed circular magnetic fields created around the loop."
"The second and third right-hand rules determine the direction of the magnetic field by current-carrying wires. Current traveling through a wire loop creates a magnetic field within its diameter that get stronger with more loops. "
"We use RHR2 to determine the direction of the field lines for a straight current-carrying wire, and we use RHR3 to determine the direction of the field lines for a circular loop of current-carrying wire."
"That I should use RHR2 and RHR3 to determine the direction of the magnetic field that the source loop/ wire creates. I understood that I should use RHR1 to determine the direction of the force exerted by the magnetic field. "
"For an infinitely long, straight wire the magnetic field will be stronger near the wire where the r is small. Also the magnetic field outside a solenoid is not constant and is weaker than the interior field."
"How a current-carrying wire also produces its own field. A long straight wire produces its own field, as does a circular loop, as does a solenoid."
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.
"How the direction of the magnetic force on a magnet's north pole is along the direction of the magnetic field lines and the force of a magnet's south pole is directed against the direction of magnetic field lines. As well as how to tell when to use 'Crouching Tiger and Hidden Dragon.'"
"I'm confused on the right-hand rules because its hard to see them in all the different scenarios on paper and try to figure them out in real life."
"How the second and third right-hand rules work."
"I just don't understand why B is the curled fingers for the second right-hand rule."
"I need a bit more help on using the new right-hand rules RHR2 and RHR3."
"Solenoids and circular loops. RHR2 and RHR3. I understood RHR1 in class, so I will pay attention tomorrow."
"I would benefit from more discussion on the field models and problems with those concepts."
"I don't have any immediate concerns, I'd just like to practice the rules and go over examples in class like we always do. What are the requirements of an object being a source object versus a test object? Is this something we'll cover? That seems like it would be interesting!"
"I'm confused on a little bit of everything."
State/describe the symbol used for the "permeability of free space," and give its SI units.
"Symbol: ยต0. SI unit = [T·m/A]."
"m·kg/(s·A)2."
"Henries per meter."
"Webers per ampere-meter."
"No clue."
State whether it is possible or not possible for the following pairs of objects to exert magnetic forces on each other.
(Only correct responses shown.)
The ends of two bar magnets: possible [67%]
The end of a bar magnet, and a stationary charge: not possible [30%]
The end of a bar magnet, and a moving charge: possible [79%]
Current flowing through a wire, and a stationary charge: not possible [39%]
Current flowing through a wire, and a moving charge: possible [70%]
Current flowing through a wire, and another wire with current in it: possible [55%]
(Only correct responses shown.)
Current I in long straight wire: thumb [88%]
Magnetic field B: curled fingers [88%]
(Only correct responses shown.)
Current I in circular loop of wire wire: curled fingers [82%]
Magnetic field B: thumb [82%]
Explain the similarities/differences between a circular current loop, and a solenoid.
"A current loop is kinda self explanatory, current following through a closed loop. A solenoid is a coiled wire with multiple current loops stacked together."
"A circular current loop electricity creates a magnetic field which is more concentrated in the center of the loop than outside the loop, while stacking multiple loops concentrates the field even more which makes it a solenoid. Both serve to create a magnetic field within their diameter by current flowing around, however solenoids are stronger fields due to more loops stacked on each other."
"A solenoid is a bunch of parallel loops."
"I don't know the difference. I Googled it and it says that a solenoid is a cylindrical coil of wire acting as a magnet when carrying electric current. A circular current loop creates a magnetic field which is more concentrated in the center of the loop than outside the loop. but that doesn't really do me any good. I still don't understand."
"I'm honestly not sure about the similarities/differences between a circular current loop and a solenoid."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"So. Why does the current split to a 10 ohm light bulbs and a 8 ohm light bulb in parallel? Why not all of the current just going through the 8 ohm light bulb considering it's less resistance?" (Yes, more of the current will go through the 8 ohm light bulb (56%) and less will go through the 10 ohm light bulb (44%), and you should work out how much goes through each light bulb--there are no "all or nothing" shortcuts, unless one of the light bulbs has zero, or an infinite resistance.)
"I'd like to get a explanation on the solenoid and circular current loop. Based from what I understood, theres no particular differences between solenoid and current loop. So, I'd like something to explain their differences." (Yes, there is no substantive difference between them other than the solenoid a stack of many circular current loops.)
"Looks like I'll be doing Khan Academy this weekend."
