You're welcome. You actually have a girl named Sarah in my class this past year to thank. She convinced (coerced) me to complete the AP Physics C series this past year!
Hello, I had a quick question. What happens if we flip the magnet so that the south pole was facing toward the loop in the diagram at 2:18? Would that make a difference in terms of the direction of induced current?
Yes. The induced current will be in the opposite direction. We have defined the north pole of the magnet as the part where the field lines point out of and the south pole of the magnet as the part where the field lines point into. So if you imagine a bar magnet over a flat loop of wire with the north pole facing the loop, the field lines will be pointing out of the north pole and into the loop. If the south pole was facing the loop, the field lines would be pointing out of the loop and into the south pole. As such if you push the magnet in with the north pole facing the loop, the field lines will be more into the page and if you push the magnet with the south pole facing the loop, the field lines will be pointing even more out of the page. Remember that only the magnitude changes as you move the magnet up and down (in proportion to 1/r^2 according to the magnetic equivalent of Coulomb's law). The direction will still be the same: into the page for north facing the loop and out of the page for south facing the loop. So with that in mind, we know from Lenz's law that the induced current will be counter clockwise for a downward moving magnet with north facing the loop and clockwise for a downward moving magnet with south facing the loop. It will be the opposite for each of those (clockwise for north facing the loop and counter clockwise for south facing the loop) if the magnet was moving upward as the flux would be less into the page for north facing the loop (aka more out of the page) and less out of the page for south facing the loop (aka more into the page).
B is a constant with respect to the variable you're integrating over, dA. It's not a constant with respect to the derivative. Does that help a little? Great point, and something I probably should have clarified as I ran through the math there.
I think you should be in great shape. Tips to handle it -- keep up with your homework, try your best to read the book BEFORE each lecture (I know, it's tough, but at least you'll have seen the material first), and hang out on the APlusPhysics site! Good luck...
So if magnetic field increases, the direction of the current is clockwise, and if magnetic flux decreases, the direction of the current is clockwise? Does an increase in magnetic field induce a magnetic flux in the opposite direction?
Hi Chris -- you can't just assume an increasing magnetic field create a clockwise current. You have to look at what the flux is doing inside your loop. The induced current will always produce a magnetic flux that opposes the change in flux.
Hello Mr. Fullerton! Thank you very much for your response. I have another question, if you don't mind. So an increase/decrease in magnetic flux depends on the original direction of the flux? So for example, if the flux was originally out of the page and the magnet was pulled further back into the page, then the flux decreases; if the flux was originally into the page and the magnet were pushed further back into the page in the same direction as the previous scenario, the flux increases? And a follow-up clarification question is if the flux were increased, then a magnetic field would be induced in the direction that decreases the flux, and to find the direction of the current, I would find how the current could flow to product the magnetic field in the opposite direction? Thank you for your time!
Hi Chris -- that's a lot of words, but I think I get the gist. In short, whenever there's a change in flux, the induced current tries to oppose that change and acts so as to keep the flux the way it was.
Hello Mr. Fullerton! Thank you for answering my questions! I just took my AP Physics C exam today, and your videos really helped me understand magnetism better.
Hey Im taking Calc BC next year and the courses my school will allow me take are only Physics C, not B. Do you think I will be able to handle it? Any advice helps but please nothing completely negative.
EMF is giving me a bit of headache. If I understand correctly, it is a voltage, or a voltage difference. Now, for a voltage difference one needs two points on the wire. But, without a say resistor, voltage difference between any two points on loop is zero. Is the EMF voltage difference between the beginning and the end of the loop? Can this voltage difference be measured with voltmeter? In other words, between which two points EMF is a voltage difference?
Excellent series of videos DAN!! thank you!!... what's the difference between a 21 year old and a 64 year old on a FRIDAY NIGHT? .. Us 64 year olds are at home relearning Physics and enjoying it........Oh and yes, it's Friday May 3rd, 2019. rather than being out at the bar or partying... (those days are so long ago!! lol) I see your video was Published in March of 2013.. WOW.. 6 years ago... I truly enjoy all your videos... you are very good at diagramming and explaining the concepts... Thank you for all that...
Am lost now seriously I don't know which formula for which problem, so many laws in magnetism can you please give us a road map for all this formulas. thanks
Hi! Thank you for making these videos. I haven't seen this stuff since school and the way you teach makes it super easy to stay fresh. Would you be interested in helping us figure this out? We're all volunteers and we're impartial there. It's a good place to collaborate. We need smart people like you really bad. forum.nasaspaceflight.com/index.php?topic=39772.3180
Hi Jeremiah -- so glad to hear you found the video useful. Looks like you've got some great discussion going on the EM Drive Development thread. My expertise / background is actually more in microelectronics than theoretical physics, but it'll be fun to see what you and your team come up with!
You're welcome. You actually have a girl named Sarah in my class this past year to thank. She convinced (coerced) me to complete the AP Physics C series this past year!
You're amazing
So are you!
This series is helping greatly on my first year physics course; can't thank you enough.
Thrilled to hear it's helping you out! Make it a great day.
Hello, I had a quick question. What happens if we flip the magnet so that the south pole was facing toward the loop in the diagram at 2:18? Would that make a difference in terms of the direction of induced current?
Yes. The induced current will be in the opposite direction. We have defined the north pole of the magnet as the part where the field lines point out of and the south pole of the magnet as the part where the field lines point into. So if you imagine a bar magnet over a flat loop of wire with the north pole facing the loop, the field lines will be pointing out of the north pole and into the loop. If the south pole was facing the loop, the field lines would be pointing out of the loop and into the south pole.
As such if you push the magnet in with the north pole facing the loop, the field lines will be more into the page and if you push the magnet with the south pole facing the loop, the field lines will be pointing even more out of the page. Remember that only the magnitude changes as you move the magnet up and down (in proportion to 1/r^2 according to the magnetic equivalent of Coulomb's law). The direction will still be the same: into the page for north facing the loop and out of the page for south facing the loop.
So with that in mind, we know from Lenz's law that the induced current will be counter clockwise for a downward moving magnet with north facing the loop and clockwise for a downward moving magnet with south facing the loop. It will be the opposite for each of those (clockwise for north facing the loop and counter clockwise for south facing the loop) if the magnet was moving upward as the flux would be less into the page for north facing the loop (aka more out of the page) and less out of the page for south facing the loop (aka more into the page).
B is a constant with respect to the variable you're integrating over, dA. It's not a constant with respect to the derivative. Does that help a little? Great point, and something I probably should have clarified as I ran through the math there.
this video is a lifesaver!!! thanks a bunch :DDD
You're very welcome!
Without you I would have never passed this exam.
the same question came up for me too. Thanks for the answer!
Thrilled to hear these videos have been of use! Good luck...
Thanks for putting all the hard work into these, Mr. Fullerton!
--Sarah :)
Glad you're finding 'em helpful. If you like these, you may like lots of the other resources on the APlusPhysics site. Make it a great day!
Thank you dude. These videos are damn helpful. Keep up the good work!
Thank you so much, Mr. Fullerton! I am taking a fast-paced summer electromagnetism course, and your videos have helped me immeasurably!
That L looks like a 1 in Rod on Rails Sample#2.
My pleasure Sarah!
I am the moth to your 100 ohm lamp
beautiful😍
Cracking me up. Good luck in your studies!
Great videos! Thanks as always!
I've got a question about sample 1, how can we assume B is constant when it is given as a function of time?
Good luck!
Thank you so much for making these videos:D
I think you should be in great shape. Tips to handle it -- keep up with your homework, try your best to read the book BEFORE each lecture (I know, it's tough, but at least you'll have seen the material first), and hang out on the APlusPhysics site! Good luck...
So if magnetic field increases, the direction of the current is clockwise, and if magnetic flux decreases, the direction of the current is clockwise? Does an increase in magnetic field induce a magnetic flux in the opposite direction?
Hi Chris -- you can't just assume an increasing magnetic field create a clockwise current. You have to look at what the flux is doing inside your loop. The induced current will always produce a magnetic flux that opposes the change in flux.
Hello Mr. Fullerton! Thank you very much for your response. I have another question, if you don't mind. So an increase/decrease in magnetic flux depends on the original direction of the flux? So for example, if the flux was originally out of the page and the magnet was pulled further back into the page, then the flux decreases; if the flux was originally into the page and the magnet were pushed further back into the page in the same direction as the previous scenario, the flux increases? And a follow-up clarification question is if the flux were increased, then a magnetic field would be induced in the direction that decreases the flux, and to find the direction of the current, I would find how the current could flow to product the magnetic field in the opposite direction? Thank you for your time!
Hi Chris -- that's a lot of words, but I think I get the gist. In short, whenever there's a change in flux, the induced current tries to oppose that change and acts so as to keep the flux the way it was.
Hello Mr. Fullerton! Thank you for answering my questions! I just took my AP Physics C exam today, and your videos really helped me understand magnetism better.
So glad to hear it Chris!
Hey Im taking Calc BC next year and the courses my school will allow me take are only Physics C, not B. Do you think I will be able to handle it? Any advice helps but please nothing completely negative.
EMF is giving me a bit of headache. If I understand correctly, it is a voltage, or a voltage difference. Now, for a voltage difference one needs two points on the wire. But, without a say resistor, voltage difference between any two points on loop is zero.
Is the EMF voltage difference between the beginning and the end of the loop?
Can this voltage difference be measured with voltmeter?
In other words, between which two points EMF is a voltage difference?
In sample 1, how come the magnetic field is constant? I had believed it was changing with time as a function.
Also, you said the derivative of a constant (area) is equal to that constant, but I thought the derivative of a constant is equal to 0
Excellent series of videos DAN!! thank you!!... what's the difference between a 21 year old and a 64 year old on a FRIDAY NIGHT? .. Us 64 year olds are at home relearning Physics and enjoying it........Oh and yes, it's Friday May 3rd, 2019. rather than being out at the bar or partying... (those days are so long ago!! lol) I see your video was Published in March of 2013.. WOW.. 6 years ago... I truly enjoy all your videos... you are very good at diagramming and explaining the concepts... Thank you for all that...
My pleasure sir. Make it a great day!
Am lost now seriously I don't know which formula for which problem, so many laws in magnetism can you please give us a road map for all this formulas. thanks
Hate to say it, but I think it's just your connection. Stays crisp here at 0:30 and beyond...
That's quite a compliment!
I don't know if its just me, but the vidoe gets blurry at 0:30
I want to become Mrs. Fullerton😳
oh!🤪
Dan.
Just wanted to wish you happy pi day... Need to find a physics holiday for you to celebrate with daughters. Love to you and your family. Pinky.
No, you are! (Thanks!)
i love Physics :)
Hi! Thank you for making these videos. I haven't seen this stuff since school and the way you teach makes it super easy to stay fresh. Would you be interested in helping us figure this out? We're all volunteers and we're impartial there. It's a good place to collaborate. We need smart people like you really bad. forum.nasaspaceflight.com/index.php?topic=39772.3180
Hi Jeremiah -- so glad to hear you found the video useful. Looks like you've got some great discussion going on the EM Drive Development thread. My expertise / background is actually more in microelectronics than theoretical physics, but it'll be fun to see what you and your team come up with!