Electromagnetism - Part 1 - A Level Physics
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- เผยแพร่เมื่อ 9 มี.ค. 2012
- Continuing the A Level Physics revision series, this video looks at Electromagnetism covering the magnetic field, the force when a current moves along a wire in a magnetic field and electromagnetic induction. The full playlist of A Level Physics revision videos is at • A Level Physics Revision
- วิทยาศาสตร์และเทคโนโลยี
even after 10 years sir, these videos are legendary, I still don't find any better teacher than you. It would be great if you can catch up again on youtube with students.
8 years later, still the greateeessst videos ... all his videos!
th-cam.com/video/5Y0bDLdyr84/w-d-xo.html Ready? GO!
*9 years later now
@@polycentric6726 THE ULTIMATE, TOP DOWN, AND CLEAR MATHEMATICAL PROOF REGARDING THE FACT THAT E=MC2 IS F=MA:
Time dilation ultimately proves ON BALANCE that E=mc2 IS F=ma, AS ELECTROMAGNETISM/ENERGY IS GRAVITY. Time is NECESSARILY possible/potential AND actual IN BALANCE, AS E=MC2 IS F=ma; AS ELECTROMAGNETISM/energy is gravity ON BALANCE. Gravity is ELECTROMAGNETISM/energy.
Great !!!! QUANTUM GRAVITY !!!! E=MC2 IS F=ma. This NECESSARILY represents, INVOLVES, AND DESCRIBES what is possible/potential AND actual IN BALANCE. What are the EARTH/ground AND the SUN are CLEARLY E=MC2 AND F=ma IN BALANCE. Very importantly, outer "space" involves full inertia; AND it is fully invisible AND black. The stars AND PLANETS are POINTS in the night sky. GRAVITATIONAL force/ENERGY IS proportional to (or BALANCED with/as) inertia/INERTIAL RESISTANCE, AS E=MC2 IS F=ma; AS ELECTROMAGNETISM/energy is gravity. Gravity/acceleration involves BALANCED inertia/INERTIAL RESISTANCE, AS E=MC2 IS F=ma; AS ELECTROMAGNETISM/energy is gravity. BALANCE AND completeness go hand in hand. It does ALL CLEARLY make perfect sense. GOT IT !!!! THE SKY is BLUE, AND THE EARTH is ALSO BLUE. Great !!! Now, think about the man who IS standing on what is THE EARTH/ground. Perfect !!!!
By Frank DiMeglio
==============================
@@daemazeemdean6803 10* years later now
Thanks for this video.
Can you let me know the time on the video of the point you are asking about. I cant find a ref to that formula on this video. I suspect you might be referring to 19:34 on part 2. The reason that the induced voltage reaches a peak at theta = 90 is that it is 90 degrees out of phase with flux linkage. But let me know if that doesn't answer the question.
Gosh, its been 9 years, but I need to say: nobody gave me such a great explanation of electromagnetism! I'm a big fan!
Yes part 2 is in the A level physics revision playlist, the link to which is now included in the description above.
You are right. I didn't want to get too complex. But of course if the north pole of a magnet points north, then since unlike poles attract it must be pointing to a "south" pole. So the earth's geographic north pole in the Arctic is in fact a magnetic south pole.
What a gifted Teacher. I hope you are the top of the education profession else this world is criminal. I'm sure many students have benefited immensely from your videos and for that you should be very proud.
Hi Mr.DrPhysics A....i just felt the urge that i had a burden on me for over 3 years now.
THANK YOU Sir.
Thank you for making my life easier from O levels upto now.You are simply great and I have yet to find someone equivalent to you from among the tutors i have had.
There are great people who are far more knowledgeable than you but you Sir...you know how to teach and make it much more easier for students like me.Thank you
12:58: OUT of the paper - a moving electron is a current flowing in the OPPOSITE direction (remember the conventional direction...)
Also, the South Pole of the Earth is, as it happens, the magnetic North Pole. Trust
Yeah I was thinking the same
was looking for this comment
I was looking to see if anyone thought the same as me ahahha
Yes. The question is, why does this holder of a physics degree forget the difference between the direction of electron flow and that of conventional current? And why is this video still up? He does present the material effectively, but this is a different skill than being able to keep the facts straight.
everyone knows these facts
By the way, this is, by far, the best video I've ever watched which explains the fundamentals of physics concerning the EMF. I'd give this video 10,000 thumbs up if I could. Well done. Very admirable.
You are right. I had already added an annotation at 12:57 which explains the error.
Well spotted. You are quite right. The electron will indeed bend out of the paper. Many thanks for spotting this. I have place a correction note on the video.
Electrons are moving from left to right which means conventional current is moving from right to left. (Current flows + to -. Electrons flow - to +). The magnetic field is downwards - north to south. So using Flemings Left Hand rule the motion (thumb) points out of the paper. Good luck with exam.
Conventional current which is used in the left hand rule moves in the opposite direction to the flow of electrons (ie + to -). So it does matter whether the particles are positively or negatively charged.
Dr.PhysicsA your videoes are outstandingly amazing and worth watching again and again. I have a question, if it won't mind you.
Which theory proves the existence of magnetic monopole? Please make a video on that, if it suits you and please add the link to the research paper of the same.
I would be much grateful to you for your favour.
Thankyou for saving my life now I understood I'm from Nepal and here the teachers are not so good with the a levels teaching but you are so well experienced made it so easy to understand ♥️ Thankyou on behalf of all the Nepalese students ♥️
Yes you are right. I had put an annotation on the video to correct this but it appears to have somehow been deleted. I have put it back again.
Another way to work out which way the magnetic field lines go around a wire is by creating a c shape with all your fingers on your right hand and pointing your thumb (like a thumbs up) point your thumb in the direction of the current flow, the field lines will be the direction of your fingers.
Please watch this -th-cam.com/video/nIbnUMqLQ78/w-d-xo.html
Ghanta
13:05 So when we use Fleming's left hand rule we use the conventional current rather than the actual flow of electrons?
I don't know if you earn money for these videos or not, but you definitely should, they are so helpful much mor than my teacher and you are so actively answering people's questions and so on
Thanks a lot for these!
Even with the small misstatements from time to time, this is simply the most lucid description of physical processes I've seen in my many years of study and teaching. These are also the most fluid of what appear to be unscripted presentations. Simply superb.
what do you mean by misstatement?.
Yes. It is sine if you measure the angle between the plane of the loop and the magnetic field and cosine if you measure the angle between the normal to the plane and the mag field.
I was hoping to see some derivations of the formulas... Is there another video by DrPhysicsA that includes the derivation of these equations?
ojasvi jain: F=Bvq
So B=F/vq. So units of magnetism (Tesla) have units of newtons/ metres/sec * coulombs
That is N/ m/t * At (since current is charge per second)
That is N/ m * A
sir please explain how coulomb can be written as At ?
Pls send me telugu videos
as I=Q/t
which means
Q=IT..
so in terms of unit
coloumb=ampere.sec
as I=Q/t
which means
Q=IT..
so in terms of unit
coloumb=ampere.sec
I was always taught RHR for all of this, but I find your corkscrew example and the left hand rule make much more sense. Thank you very much for making this, Fleming's left-hand rule is much easier!
Very well explained every single bit.
I appreciate
I like the arrow analogy, it's helpful, thanks :)
For the first time on youtube I'm thankful for annotations.
Thank you so much, you're a life saver. I've missed a few lessons on magnetism, and reading up from a book just isn't the same in my opinion as having it told to you and shown :)
sad to say, better than my highly qualified physics teacher
My physics teacher has a PHD and this guy teaches physics way better
This guy has a PhD in Nuclear physics from kings college. That's why he's called Dr. physics, lol.
@Film Master none in your entire country?
@Film Master actually physics is not so difficult
I cant even understand what my professor is saying
Thank you .The video was very helpful,got an A+ plus without even studying for the Electromagnetism test
Thank you so much after watching this i understand enough to do my homework and exams :)
You use your right hand to wrap your fingers around the solenoid in the direction of the current flowing round the solenoid. Your thumb will point to the North Pole (ie in the opposite direction of the magnetic field). It depends whether the solenoid is wound clockwise or anticlockwise.
You are so clear in your teaching-thank you so much :)
This really helped me thanks
thanks a LOT. It really helped me!! You are an amazing teacher.
Thanks a lot sir for your brilliant explanation.Please keep uploading videos as videos are very profound.
Its the left hand rule for a current flowing in a magnetic field where 3 fingers represent FIELD, CURRENT and MOTION. Or you can use the right hand rule (I prefer corkscrew rule) as you indicate with the curled fingers.
Why not apply F=qvxB with my right hand? Reading the cross product from left to right it goes: The current of positive charges going out of the paper ( velocity v - using my thumb as 1. finger ) the field going from north to south (left to right - using my pointing finger as my 2. finger) then the force as a result is my middle finger. This way I always only use my right hand so not to be confused about which hand (left or right) to use.
Correction at 12:54
The electron will move out of the paper instead of into the paper because the conventional current is opposite in direction to the negatively charged electron. It would be into the paper only if it were a positively charged particle, like an alpha particle.
And just to add that I have looked up the AQA syllabus and they define NΦ = BAN cosθ where θ is the angle between the normal to the plane of the coil and the
magnetic field. I define θ as the angle between the actual plane of the coil and the
magnetic field. So that explains the difference.
Sir, perhaps you have the direction of B switched at approx 8:00 ? Shouldn't it be clockwise, or did I misinterpret?
Excellent video, many thanks.
The electron is moving to the right but conventional current moves in the opposite direction to the electrons (ie to the left). Conventional current flows from + to - whereas electrons move the other way.
just simply outstanding , i have an exam within few days and your jobb has been quite helpful and effectiv
Tusen Tack
Doing the new GCSE and this is a great help, thanks.
Thanks. And yes you can equate the two equations if you choose the right experiment. This would be an expt where you have stream of electrons (charge q) moving from left to right through an electric field E going from top to bottom and a magnetic field going into the paper. The electric field will exert a force on the electrons causing them to move up. The magnetic force will cause the electrons to move down. If you match the forces then the electrons will go back to moving left to right.
Just a few notes that are mentioned in a later video:
-Where he says mu nought (Uo) is the permittivity of free space the notation in the given formula is epsilon naught (Eo). (sorry symbols aren't great)
-Also we use a capital letter Q for charge unless we refer to 2 charges interacting i.e. Q and q or more simply Q1 and Q2.
Other than that was very helpful.
+DrPhysicsA could you pls let me know where i can solve problems related to what you taught in this video as well as part two? Thanks in advance.
I am assuming you are talking about a coil of wire of N turns and cross-sectional area A rotating in a magnetic field B. The flux linkage = Φ = BAN sin Θ where Θ is the angle between the magnetic field lines and the coil. So when Θ=0 (ie the coil is parallel with the field and no flux passes thro the coil) there is no flux linkage. When Θ=90, ie the coil is perpendicular to the field, there will be maximum flux linkage. This is shown in part 2 of this video at 19:34
The strict answer to your question lies in quantum mechanics. The mag field isn't made of anything. It exists where some physical phenomenon causes it (eg between two separate magnets). The question which puzzled those who observed two north poles repelling each other was, how did one magnet know that the other was there. The QM answer is that virtual photons act as information carriers to determine the force applied by a mag field at any particular point.
Thankyou sir @drphysicsA. Received my Alevels result. Had A in physics. Bundle of thanks!
Thanks a lot..I finally got this rule!
Much appreciated! :)
Just a little bit of pedantry: the diagram drawn at ~1min depicts the earth with its magnetic North pole at the geographic North pole. But actually, the geographic North pole is the magnetic South pole. And vice-versa.
yea i just said a guy same thing its so amazing when you think about it
Please watch this -th-cam.com/video/nIbnUMqLQ78/w-d-xo.html
I think the drawing you did about a minute and a half in of the earth being a magnet is incorrect. I believe the south pole should actually be on top and the north pole should actually be on the bottom, because we named the "north" direction based on which direction a compass points. If the earth was a bar magnet like you drew, the north end of a compass would point towards the bottom of the earth instead of a top.
rotflmaopmpqxyz actually, in a compass, the south pole of the needle is named as the north pole so, soith pole of the needle will move to the north pole of the earth
brilliant! never actually knew WHY the wire is under the force. thanks a lot!
So given an electromagnetic field, there is the ability to transfer energy which effects the motion of charged particles. But in the action of affecting the charged particles, are photons required in this process? So are photons transmitted in some fashion to induce the effect on the other charged particle? At what point are photons required? How does an alternating electromagnetic field correlate to photons? So for example, when I spin a magnet on a table, it creates a measurable affect on a detector circuit measuring the field strength. That changing magnetic field, are photons transmitted to the detector circuit from the spinning magnet? When do you need photons? When does the field transmutate into a photon? And spinning magnet affects the detector but the sector also affects the magnet so does that mean there are photons also transmitted from the detector to the magnet and if that is true, then would there be a delay by twice the distance for the magnet to know there is a detector out there listening and stealing my energy, one times the distance, simultaneous?
Incredibly helpful, thank you.
It was Maxwell who showed that electric and magnetic fields are related but different. A current flows because there is an electric field and generates an associated magnetic field. A magnetic field around a magnet will, where there is a changing magnetic flux, cause an emf, hence an electric field and hence cause a current to flow. My vid on Maxwell's equations may help.
Could you please explain how charged particles with different charges and masses would act in Electric and Magnetic Fields Thanks
You're the best thing that has ever happened to humanity
Omg, thanks for the introducing the interesting way of remembering the fleming's left-hand rule !!! I always got it wrong !!!
I love his explanation it really helped me
Please keep uploading these elegant videos!
If only i found these earlier!!! Brilliant work.
So do I need a magnetic corkscrew to understand this? Does it matter what type of currants are in the field? Are the 2 pies made using the currants? Does it matter how many plates are in the field? Do you put currants on the plates? So arrows are magnetic? Is the stream of particles next to the field with the plates of currants?
Thank you sir! Very nice demonstration.
I find it really amazing that our hands were perfectly made for the flemmings hand rules, or is it the other way around the rules were made for the hand, but that can't be true, can it?
A remarkable coincidence.
Its not really that special when you think of it, all you need is 3 lines at right angles
Somerandomdude4.2526 That would be 3 dimensions
Matthew Martin 3 spacial dimensions
hahaha
What a good idea! I like it.
What the hell this is the best thing ever I understood everything for my test yesterday I'm a so grateful that I found u
Just to clarify, the magnetic field travels from north to south. The electron is not travelling inside the magnet. You can think of a bar magnet having been bent into the shape of a U with the North at the top of one arm and the south at the top of the other. The electrons travel between the two arms. As the annotation to the video shows, the electrons will in fact be bent out of the paper.
You are right. That is why there is also an induced current. The main current creates a magnetic field but that in turn creates and induced current in the opposite direction.
I had to watch this to kill my curiosity in understanding electromagnetism principles. And it was very helpful
A bar magnet has a magnetic field associated with it. If it falls thro a coil of wire then there will be a changing magnetic field as far as the wire is concerned. Faraday's law says that an Emf will be created which equals the rate of change of magnetic flux. If there is an induced Emf then a current will flow in the wire.
Your videos are really good.
You taught me in half an hour what my teachers couldn't teach me in weeks.
But, your video quality's a little poor. At least get it upto 480p whereas 720p would be perfect.
Keep up the good work.
Also when measuring the velocity and the charge of the particle what units do I put them in?
You use the righthand corkscrew rule. The corkscrew points in the direction of the current and the magnetic field goes clockwise.
first of all you are amazing :)
i have a quick question like you said we can put F=bqv with F=eq
my question is can we put F=eq with F=BIL?
if yes then why?
if no then why?
Having visited CERN, I was enthralled by the electromagnetic forces acting on charged particles which creates their circular path as a result of the centripetal force. The force is inwards for a particle travelling around magnetic field lines due to FLHR and so the particle subtends towards a central point. As it does this its direction of motion is constantly changing and so is its velocity. From this we can derive that its acceleration is constantly changing which essentially keeps it travelling in circular motion.
Thank you for this video now I have better understanding on electromagnetic force
outstanding explanation. thank you very much.
Wjec gcse exam for triple physics in less than a week, this has really helped revision for thzat.Thank you.
Thank you, now i will try to apply this on a crt tv to control the eletron beam
Can you perhaps talk a bit about wi-fi electromagnetism and how tit works. IE. your wi-fi modem.router and your electronic devices wusing this electromagnetic field? I am trying to understand. Your first 3 minutes taught me more about magnetism I have ever understood haha. Thank you.
Very well explained sir thank you...left hand rule is better way to understand behaviour of current flowing.
it would be kind if u provide a video of Charged particles revision class.......
One is used for motors and the other for generators and I always have to look up which is which. ie one is used when a current flows to turn the coil (motor) and the other when turning the coil causes a current to flow (generator)
Please watch this -th-cam.com/video/nIbnUMqLQ78/w-d-xo.html
I have many questions sir,
what happens when a mechanical wave collides with electromagnetic wave? I have a theory that I would like for you to analyze and give an opinion on.
But the magnetic north pole is located in the geographic southern hemisphere of the earth and vice versa, not the opposite as you claim...
Rebecka yup, you’re correct. He’s not
Just want to say thank your for taking the time in making these very insightful videos! you keep the subject exciting and explain it very well! cheers
Joseph Guzman Kind of you to say so. Thanks.
thanks! helped a lot with my assignments as well as exams!!!!!!! god bless you! DrPhysicsA
Great collection of videos; really logical, thankyou.
Quick question about the force on a beam of electrons, due to a magnetic field. I know the rule is F=Bqv, but for Fleming's left hand rule, do you point in the direction of electron flow? Or in the conventional direction? Bit confused. Thanks again
Very helpful for my exam. Thank you.
Amazing lectures... thanks
is it normal that wires cables or conductors exhibit a uniform directional force just by a 12v 2A source. all cables is insulated. I made even rigid nonflexible aluminium and it still moved in the arrangement I made, switching the current the other way makes the arrangement move the other direction, I don't know what this effect is, it cant be wire heating since the connecting wires are very short, insulated and the frame is a rigid alu frame that moves at command
Hello DrPhysicsA;
I am refering to the point Devaki is making, Would you explain what Magnetic south pole and north poles are and show the field lines for each please. Also at 16:20 would you show the direction of the current between the plates, I can not quite picture the direction of the force generated once the magnetic field is introduced. Your videos are great !
That was such a phenomenal lecture. Thank you so much, Dr Physics. Your delivery and the robustness of the topic covered in such a short period of time was amazing! Please ignore the critical comments, it's just a facade of pseudo-intelligence. Hugs from NZ!!!!! :-D
Thanks.
gp34 it just doesn’t though lmao.
sir i m not understanding what is the meaning of into and out of paper practically.......next is that how we can apply the left f rule for the partical which move in circle
yes i got it thank you very much, You helped me a lot
also i was a bit confused about flemmings left rule but now there is some people arguing to use right hand rule instead, but i totally ignored them except i just use right hand rule when there is a current flowing through the wire and i use my thumb in the direction of current and the curl fingers for the magnetic fields, does that sound alright?
Ur video was very informative and well explained.
I have a question, U know u said that we can't have a north or south pole on its own, so what pole is the magnetic field around a single wire when a current is flowing?
Thanks
Conventional current. All this was derived before anyone knew what an electron was. So current was assumed to travel from + to -.
@2:28 Where does the current in the wire originate from that we have placed within the magnetic field? I thought this was the origins of how current is created in the first place. I hope I'm making sense.