Physics 45 Electromagnetic Induction: Faraday's Law and Lenz's Law (1 of 2) Introduction
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- čas přidán 26. 03. 2013
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In this first of the two part series I will introduce Faraday's Law and Lenz's Law so you can better understand the concepts and equations.
8 years later since the video was posted! I watch this now and it helps so much, as I was confused how to decide the induced current’s direction. Thank you so much Professor!
Glad the video was helpful. Physics doesn't age. 🙂
Keep up the good work professor! If you could see all the people you've helped with your lectures in one area, you would need a whole stadium!
Stephen,
In Lenz's words: "The direction of any magnetic induction effect is such as to oppose the cause of the effect"
In other words: "the induced magnetic field will oppose the effect that caused it in the first place", or: " the induced magnetic field will oppose the change".
Thus if the magnetic flux through the loop is decreasing the induced magnetic field will be in the SAME direction as the diminishing field (to try and keep it from decreasing). If the magnetic flux through the loop is increasing, then the induced magnetic field will be in the OPPOSITE direction (to try and keep it from increasing).
Amazing explanation.
what if I have coil and permanent magnet and moving them to a conductive object. why dont they joint ?
Summary of this video (:
Thank you sir
@@mikehawwke
Lenzs law Based on
Conservation of Energy
I was really not understanding Lenz's law until I watched this lecture. This made a difference in not getting overstressed before the finals. Thank you very much for saving my sleep!
You are welcome. Try not to stress over the final. 🙂
Dr Van Biezen, you are a life saver! This is the cleanest explanation of the concept of Lenz's Law!
Sir, you did it again !! From helping me understand lenses in optics in my first year of university, to helping me understand Lenz in my 3rd year of university! Thank you Professor!
Great! Glad you came back for your next semester in physics. 🙂
Sreya Panda,
Remember that the induced magnetic field opposed the CHANGE in the magnetic field that caused it in the first place.
If the existing magnetic field is INCREASING, then the induced magnetic field will be in the OPPOSITE direction.
If the existing magnetic field is DECREASING, then the induced magnetic field will be in the SAME direction.
why is it that sir?
sreya panda
Sreya Panda,
The why questions are the most difficult to explain and comprehend and often require advanced science and mathematics to answer,
If you are interested, the playlist on Maxwell's equations explains the answer to your question, but it requires some level of understanding of mathematics
Michel van Biezen thank you so much! ill definitely check it out sir. :)
I did not understand the direction of induced current
thanks dr. for that clarification,you're the best
Hi this video is probably the best video i have seen on this topic, very clear and well structured. I was however confused by your second example where the B field is in the same direction as the induced B, this made me confused as to the link with Lenz's law which states that it would be in the opposite direction. Could you please tell me why you did that?
this is the best explaination of lenz's law on YT
Thank you. Glad you found our videos.
My goodness you made it so easy, I was totally lost in the class. Thanks
+Farzad Jalali Hehe, mee too! :) All the standard textbooks I've seen have made every effort to blur this simple point miserably, by using totally confusing, dry, non-expressive language and lame examples, as if this was a patented idea or if the nice & simple explanation costed a fortune. ;)
This is the simplest explanation to determine the direction of the induced current I found on CZcams.
Thank you, professor.
Glad you found our videos. Welcome to the channel! 🙂
Thank you so much for this...I go to Stanford and our professor for Electricity and Magnetism is terrible. You are so much clearer and easier to understand!!!!
This is a crystal clear explanation of Lenz's law. Many thanks!
You have helped me understand some important concepts in physics. I need this to continue my studies in engineering at the university so that I can get out out the clutches of poverty. Thank you. Your work and talent will never be forgotten.
Glad we could help!
Thank you this is so great! I take IB Physics and there's a lot of material to cover, so our teacher rushes over it (with terrible handwriting and diagrams) and assumes that we'll figure it all out from the book, but I just learn this stuff so much better from hearing and visualizing than reading... Thanks again!
That is why I keep making these videos.
Thanks for the comment.
I was very much confused in this topic. Your video helped me clear my doubts.
Thanks a lot Sir!!
thank you so much for all your help. ive been watching your videos through college phys 1 and 2 and they have saved me so many times!
The best video i have saw to understand this law. Excelent! Thank you!
Glad it was helpful!
don't know why pay like $1000 for Physics class if my teacher can't give a coherent explanation.
after many hours studying i can understand what is all about Faraday's Law and Lenz's Law. Thank you for sharing this video
first class lesson, best i've ever seen or heard. clever choice of examples too.
Professor van Biezen,thanks again,suppose a solenoid with length L, z symeric axis,z(0,0,L)
coil length L, at z=0,stopper and mag. field N ans reversing, plunger ferrite magnetization
partial as per hysteresis remannecence, plunger legth =h,what is relative TD and BDC of plunger inside the solenoid, z coordinate from 0, and ha stroke end of plunger? x(t) and Dx(t)/dt, and d2x(t)/dt2, Bsol-Bemf=B? Thanks and Regards
I WISH you were my phyII professor! You're very clear and organized.
Dear Mr.Michel van Biezen, Nice lecture and many thanks for you.God bless you!
Kubra,
Any time the magnetic flux changes (increases or decreases), the will be an induced Emf.
I really appreciate all the videos, always so helpful and informative!!!!
nice one. I am having my physics O levels tomorrow. I guess this helps me clear doubts. You nice man
Thank you so much for the youtube channel name (met you on the southwest flight from LA) really helped me out! (:
Jennifer,
Glad these videos are helping. Thanks for letting me know.
Good luck with your exams. Keep up the hard work.
An easy way to understand the 'decreasing' case is this: assume the South pole of the magnet is moving downward, below and away from the loop. That means the space in that region is declining in South pole flux lines, or equivalently, could be seen as taking on more North pole conditions - it's becoming 'Less South, so relatively more North'. That explains why an 'approaching North pole magnet' and a 'decreasing South pole magnet' require (Lenz's Law) a North pole manifesting in the loop to counter the increasing North pole conditions. In essence, the 'decreasing or moving-away South pole' is like a growing North pole.
It's akin to thinking of the South and North magnetic field density on a continuum - like on a number line - as it is along the length of a bar magnet.
A good way to look at it.
Sir, You explained it so simply, so clear and well. Sir, you just gave me hope I might pass the class. I really have trouble grasping the concepts in class. if I had You as my professor, I wouldn't have to worry about passing.
Thank you. Glad you found our videos. Yes, not all professors are good at teaching, unfortunately. We had our share of them when we went to university, although we also had some very excellent professors as well. We do remember the frustration we felt when we couldn't understand the lectures and we were desperate to find a source that could help us. That inspired us to make these videos. All the best on your studies. 🙂
Thanks a lot. Your way of teaching is wonderful.
Very clear!!! Congratulations!!!
Change in Magnetic Flux - lines through the coil will INDUCE emf in the coil,
that INDUCED emf will cause an INDUCED current in the coil,
that INDUCED current will set-up it's own Magnetic Field which opposes the change that causes in the first place.
This video is a lifesaver.
5:27, I don't get it. why is it in the same direction..
The magnetic field cutting throw the wires is decreasing as the magnet is pulled(away) from the loop. Therefore, the current produced in the loop has to oppose decrease in magnetic field(lenz law)...and thus vectors will add up if current is clockwise....
Magnet pulls away(less magnetic lines)....emf induced in loop to oppose the decrease......current is clockwise to add vector fields to the magnetic pulled away from the wire.....If it doesnt oppose then we have created energy outmof nothing, you pull a magnt in, and even more magnetic force keeps adding infinetly.
Very helpful, your videos are greatly appreciated! Thank you!
the interactive force is the magnetic force of repulsion(b/w induced mag field and pre existing), that said as opposing flux change. isnt ?
Great! I had not understood this topic until your explanation
good job!! iSo clear for me to understand the Lenz law.. #Keepitup
Besides the great job helping me understand Lenz's Law, I dig the bow-tie.
Youre such an amazing teacher ! Thank you :)
Oh my God, I understand now. Thank you and God bless you
Now I understand sir, thanks a lot,no words to say
thanks a lot.... extremely helpful!!!! loved ur way of teaching... :)
sir,
how do we find out the direction of the magnetic field when you know it has to increase or decrease. in the fist example it had to be the opposite direction but in the second its the same direction of as that of the decreasing magnetic field. please help!
Thank you. :)
Thank you!! This was absolutely perfect.
Very clear and so helpful. Thank you!
Sir thank you very much for ur videos, they have been a great helt for me
many thanks for your videos!
When you talk about induced current flow direction, are you talking about "conventional" current flow or actual electron flow/
Kevin,
Not sure what you mean by "conventional" current.
But the induced current is a REAL current.
The convention in physics is that a current is the flow of positive charges.
(in reality the charges that flow are of course electrons)
i'm your old student sir
you are a gift for students specially in this pandamic situation where every student is struggling
Thanks!
@@MichelvanBiezen oh sir happy to see your reply, I mean at least I was not expecting that beacuse the uploaded video is 6 years ago.
Stay safe and happy sir,
Love from PAKISTAN STUDENTS.
He actually made it a lot more complicated then it is. If you're approaching the conductor from the north side (negatively charged), the particles in the conductor will move in the opposite direction of the clock, if you do the inverse, if you move the magnet away from the conductor with the north side still facing the conductor, the flow will move in the direction of the clock. The opposite happens with the south or positively charged side.
Sir hats off ur explaination is excellent
Superbly explained. Thank you.
much love from ethiopia. the legend!
Thank you. Welcome to the channel! 🙂
Hello teachers, I have questions
The magnetic field shown in Figure P20.63 has a uni- form magnitude of 25.0 mT directed into the paper. The initial diameter of the kink is 2.00 cm. (a) The wire is quickly pulled taut, and the kink shrinks to a diameter of zero in 50.0 ms. Determine the average voltage induced between endpoints A and B. Include the polarity. (b) Suppose the kink is undisturbed, but the magnetic field increases to 100 mT in 4.00 3 1023 s. Determine the average voltage across terminals A and B, including polarity, during this period.
AB
Great review for me...I'm watching the series on Maxwell's Equations. Great background info.! 😊
Yes, this is part of it.
Thanks a lot for your lecture, you really made it so easy. I appreciate it a lot. I just want to understand the difference between figure 3 and 4, as i am confused about case3, i think it might be North going outwards the solenoid. Again thank you very much for your structured way of explaining.
Figure 3 and figure 4 are essentially the same in that the magnet approaches the loop with the south pole pointing to the loop, except that in figure 3 the magnet approaches the loop from below and in figure 4 the magnet approaches the loop from above.
I think there is something wrong in your diagrams between Figure 1 and Figure 4 - please look at these diagrams again, @Micheal van Biezen. I think it has to do with the magnet force you drew in Fig. 1 the magnetic flux is increasing but pointed in the wrong direction- according to your diagram. Since the magnetic flow is flowing into the North pole of the magnetic, and not out of it, as you picture it - if I'm correct. Thank you for all your hard work Dr. Biezen.
Thank you very much. Keep up the good work
have to be honest, this guy lectures better than my professor
thanks this helps a lot! i was struggling to find the current direction before watching it.
Glad it helped!
Very thoroughly explained, thank you so much!
Thanks! Now I finally understand! :)
I thought that the right hand rule was thumb for current or velocity, fingers for magnetic field then palm was force, or are there various ways for this?
Astraithious
Yes, there are several "right hand rules"
One of them is holding your hand light (a child imagining that their hand is a gun with the middle finger pointing to the left) The thumb represents the B (magnetic) field The forefinger represents the force. The middle finger represents the current. (I stopped using that since the students were having a hard time using it)
If I rotate the board upside down and then place a thumb in the direction of induced B field, then the direction of the induced current will change/opposite? why?
Regardless of how anything is turned, as long as you follow the rules as shown in the video, you'll find the correct solution.
Massive thanks from me to you Sir. You helped me again. God bless!!!
You are most welcome. Glad you find our videos helpful. 🙂
Thank you Sir this HAS helped me ALOT.
I FINALLY understand it! THANK YOU
Sir, in the 2 example the mag fd. is decreasing and the induced current will be in such a direction that it will oppose it from decreasing, then how the B induced will be in downward direction ? Couldn't understand clearly sir . Please help .
How do you keep something from decreasing? Answer: you add to it. And thus the induced magnetic field will be in the same direction as the original field to try and keep it from decreasing.
God bless u sir, for helping me understand this concept! You hv certainly helped alot of us.. :D ~ all the way frm australia...
Emi Stephen,
It is good to know that students from "down under" are watching these videos.
Thanks for letting me know.
Thank you so much. Nowadays I am using your videos a lot since I am teaching Physics online due to pandemic.
That's great Hang in there. We'll get through it.
that was so helpful!! thanks heaps
Perhaps I missed something, I am curious on why I found the induced current to be the opposite direction to the direction shown in the video when I performed the right hand rule?
The directions in the video are correct.
so eddy currents that is produced the emf will oppose any change to magnetic fields?
Yes, the same principles hold true with eddy currents
thank you very much for this video, its really helped me
Good explanation. Wanted to know & I found out.
A CZcamsversity student.
Dear,
Why does the second example contradict if we follow the way of writing N inside the loop , because the magnet is moving away ,then the loop will form North pole to attract the magnet , if we moved with N direction , it will be the other way a round , I understood your way, but it N way doesn't work ?
There is no contradiction here. Remember, the induced magnetic field opposed the CHANGE in the magnetic field. It adds when the existing field is being reduced. It subtracts when the existing field is increasing.
Great description thank you
Glad it was helpful!
Hello Professor Michel Van Biezen, the way you explained it was so clear, that I understood it, and I was thinking of an analogy of a BOXING MATCH of Manny Pakman Pacquiao exchanging blows with MARGARITO .... something like that .... hahahaha
A good analogy. 🙂
I like the three south fields and one north field...Doh ! what happened to the north out magnet
Thank you so much that was really helpful!
Glad it was helpful! 🙂
Is current and EMF in the same direction?? does the direction of emf changes if direction of current changed??
Think of the Emf like voltage. It "pushes" positive charges.
Therefore the Emf (or potential difference) pushes positive charges from high potential to low potential.
Thank you this was really helpful
I don't understand why Lenzs law states that the induced emf will cause a CURRENT to flow in such a direction as to oppose the change in flux linkage that caused it. Why a current? And how and where? Sorry if its a silly question..
Wardiya,
If you want to understand this in more detail, watch the playlist on Maxwell's equations. I made 30 videos that explain how this works very carefully.
Basically, a changing magnetic flux causes an electric field to exist in the conductor. This electric field caused a potential difference (Emf) in the conductor. This Emf will cause a current to flow. That current will cause a magnetic field which will oppose the changing magnetic flux that caused all this in the first place.
A best explanation ..👍❤️
Thank you 🙂
Can we make copper coin into a antimagnetic by applying ferromagnetic material like Cobalt to coin?
The repulsion is caused by magnetic fields and moving charges within them.
According to this two laws we can make antimagnetism is it possible? One doubt sir if needle is placed towards copper coin the needle is repelled by the copper coin is it possible
Never heard of "antimagnetism".
Push magnet through loop and you reverse thumb rule.
Pull magnet away from loop and you keep it same thumb rule.
Thank you for this very clear explanation
great explanation!!!
First of all i wanna thank you for the great and simple explanation.
my question is why would the magnetic field produced by the induced current oppose the change in flux ? why would it keep it from increasing ?
Mohamed,
That is a great question.
By moving the magnet towards (or away) from the circular conductor, you are changing the strength of the magnetic field at the location of the circular wire. Since the wire is filled with electrons, these electrons are subjected to a changing magnetic field. That causes the electrons to feel a force perpendicular to the field, which causes the electrons to move in the direction of the force. Moving electrons constitutes a current. A current causes a magnetic field.which is directed perpendicular to the current. The magnetic field will be directed in the same direction of the original field is decreasing in magnitude, and will be in the opposite direction if the original field is increasing.
Another way to think about it is to ask the following question: "What would happen if the induced field was in the same direction as the increasing field"? Answer: you would get free energy out of nowhere. Nature doesn't work that way. Nature works more like Newton's third law.
Michel van Biezen Thank you so much i appreciate your great effort in conveying the message as clear as day to non-native english speakers
Sir, can you please explain why does the induced EMF opposes the rate of change in the magnetic flux?
Thanks.
It is like trying to explain why to positive charges repel each other. That is the way nature is designed. We know it does because we have observed that it does.
@@MichelvanBiezen Thanks for the clarification sir.
Needles are not properly made of steel but it also contain zinc so can we make copper coin into a needle repellent?
The repulsion is caused by magnetic fields and moving charges within them.
My mother tongue is not english but I try to explain what I don't understand. If we have a relation between emf and flux I expect to see the graphic representation of the emf not of the current. Ok as intermediary step you can use whatever you want but at the end I want to know where is this emf and what is it's orientation. Or at least you have to explain why formula say one thing and you do another thing. Moreover are there 2 B? If I place there something to measure B what do I mesaure?
Traditionally, when these experiments were done, the effect of Faraday's Law and Lenz's law was measured by measuring the current in the loop. Since current needs a potential difference they surmised that there must be an induced voltage which was called "induced emf" where emf stands for "electromotive force". But the current is the measurable result.
Dear sir! I think I found what I was looking for =)) Thank you.
Glad you found ut.
So INCREASING flux is in the same direction as the B field and DECREASING flux is in the opposite direction of the B field. Then all we would need to take into account after this point is to know that B (induced) field opposes the direction of the changing flux. Right?
+Christopher Sanchez That is not the wording I would use.Let's try it this way:If the flux in the loop is increasing, the direction of the induced magnetic flux will be in the opposite direction. If the flux in the loop is decreasing, the direction of the induced magnetic flux will be in the same direction.
EXCELLENT, THANKS VERY MUCH
Very Helpful! Thank you so much :)
Couldn't you use something tighter to write on the board?
your best then my teacher
thanks a lot