AP Physics C - Magnetic Fields due to Current-Carrying Wires

[@DanFullerton]

Absolutely -- at 5:28 in this video, in the denominator I should have written Pi*d instead of 2d... the rest of the calculation appears to be finished correctly. Thanks for pointing it out!

[@monsterous289]

You should probably state your mistake in the video by typing text over next to it using tools on KZbin. Some might not think to look in the comment section and waste time pondering on how "your mistake" is true.

[@monsterous289]

Sean Pickman Nevermind. I hastedly wrote this before continuing the video. To me your comment implied that you did not find and fix the mistake when recording the video.

[@cvhashim]

4:43, aren't the two wires going opposite directions. So to find the net you should subtract right?

[@DanFullerton]

Nope. Use the right-hand rule, and you'll find the field from the top wire is going into the plane of the screen at point P. Using the same rule on the bottom wire, you'll also find that the field is going into the plane of the screen at point P. So, add them up! :-)

[@cvhashim]

thanks!

[@Hikarinara1217]

Thank you sooo much:) best physics teacher out on youtube

[@DanFullerton]

Thanks so much!

[@splashcity2k10]

Hi dan im confused on right hand rule here. First off, is it related to the right hand rule for qvb=Fb and second, can you explain precisely how you determined the direction of the magnetic field below and above the wires and then the direction of the force on the wires at 2:40. Thanks so much

[@DanFullerton]

Ben Eckardt Hi Ben. There are 3 right-hand rules to learn in electromagnetism. in this one, the direction of the magnetic field is in a circular direction around a current-carrying wire. Point the thumb of your right hand along the wire in the direction the current flows. As you wrap the fingers of your right hand around the wire (the direction your fingers point), that tells you the direction of the magnetic field around the wire (i.e. clockwise or counter-clockwise). This requires some visualization in three dimensions.

[@splashcity2k10]

Dan Fullerton Bam! It all just hit me. I can always count on you!

[@thisperson2505]

If the current carrying wires exert a force on each other that equal each other due to newton's third law, what happens if you increase the current on one wire?

[@DanFullerton]

Increase the force (on each other).

[@thisperson2505]

@@DanFullerton thank you, also really cool that you still reply to comments on super old videos

[@peach_mitao8264]

For the wire on top, if I point my right hand thumb in the direction of the current to the right, my fingers curl "upwards" right? Which is out of the page I think. How do you get into the page? Thanks for the clarification. I know the bottom one is into the page

[@DanFullerton]

+HuiYing Tan Hi HuiYing. For the wire on top, if the current is going to the right, your fingers curl around the wire. Above the wire, they point out of the page. Below the wire, they point into the page (or the screen).

[@JacobSmithodc]

I can just imagine myself sitting in the AP test twisting my hands into strange shapes.

[@DanFullerton]

+Jacob Smith You won't be the only one!

[@metaphoric99]

If a current-carrying wire is in a constant magnetic field, then the field is exerting a force on it. But the current-carrying wire also creates a magnetic field apparently. So why did we not have to also account for the field created by the wire when we were calculating the force exerted upon it in the previous video (current-carrying wires in magnetic fields)?

[@DanFullerton]

The current in the wire creates a magnetic field around the wire, not in it.

[@metaphoric99]

Ah I get it. Thanks!

[@Captain_Rhodes]

question : if magnetic fields always go from a north to a south pole, where are these poles around a wire?

[@DanFullerton]

geobruf123 Inside the magnet, the fields run from south to north, so you actually have a complete loop with any magnetic field. Around a wire, you also get a loop, with the direction of the field lines given by the right hand rule. In both cases, it's a complete loop.

[@Captain_Rhodes]

Dan Fullerton ok thanks. so are you saying that poles only exist for reference and are not actually there?

[@DanFullerton]

geobruf123 I think you've got the right idea, but I'm not quite saying that. In a physical magnet (like on the refrigerator), magnetic field lines make a complete loop inside and outside the magnet. However, because some of that field is internal, we can look at the physical boundaries of the object itself and call the ends 'poles,' which are the result of the magnetic field lines at those boundaries.

[@Captain_Rhodes]

Dan Fullerton thats great thanks so much. can i ask one more quick one please? when doing a cross product say Idt(V x B) , and because Vdt=dl then I notice you convert it to I(dl x B). that seems to imply that whatever is before the xB can be multiplied and cancelled without any effect on the final result. My instinct says that (V x B) would be an isolated result and that we should do it as a seperate calculation? i hope that makes sense. this is a big problem for me as cross product literature never covers these things. would love an answer is you have a minute. best wishes

[@DanFullerton]

geobruf123 You have to look at what variables are changing and dependent upon others to make those substitutions -- not a formal rule, but rather understanding what you're writing and using your background knowledge to adjust the equation.

[@Centaurship]

Thank you so much! This helps me a lot.

[@DanFullerton]

+Kersey Badocdoc You are very welcome!

[@firemichael]

This is great. Thank you!

[@DanFullerton]

You're very welcome!

[@DanFullerton]

You too!

[@MadelleCameros]

thank you so much..:) amazing...!!!!

[@DanFullerton]

+Madelle Cameros You are very welcome!

[@kevin7600ex]

You're awesome :D