Electromagnetic Induction | 'Cutting Field Lines' (Faraday's Law) | A-level Physics

[@ForestLearn]

I forgot to mention that Fleming's right-hand rule (the 'dynamo rule') is sometimes presented as a way to find the direction of the induced current when a conductor cuts magnetic field lines. In my opinion, the right-hand rule is completely unnecessary - everything you want to find out can be answered with the left-hand rule (as discussed in the video). The left-hand rule is just a visualisation of the magnetic force F = Bqv, which explains everything that goes on. Why complicate matters with two hand-rules when one is enough?! Not to mention, you then run the risk of getting the hand-rules mixed up, and then having to memorise even more unnecessary stuff to stop that happening etc.

[@aphysicist9558]

I tried using both Flemming's left hand and right hand rule. Did you draw the diagram so that if you use the RH rule it would be very painful and uncomfortable but using the LH is not? Jokes aside this is a good approach if the understanding is there

[@ForestLearn]

@@aphysicist9558 No, my level of planning/thinking is not that deep :) I was not thinking about the RH rule at all, because as I explained above, it's unnecessary. I agree - using the LH rule to understand what's going on here does require a solid understanding of it.

[@niccybeth572]

Extremely helpful! Thank you very much for this video.

[@ForestLearn]

You're welcome, glad you found it useful :)

[@uvindusahan947]

You are a hero bro ❤ thank you for saving my day brother

[@ForestLearn]

Thanks, you are too kind :)

[@lakipalaniappan]

0:59 - 3:45 is incredibly useful. Thank you

[@ForestLearn]

My pleasure, really glad to hear that :)

[@d_i_a_v_l_o3827]

saving my a levels fr durham here we come 🔥🔥🔥

[@ForestLearn]

Good luck - you can do it!

[@charliecooper7458]

Im going durham too, DURHAM HERE WE COME

[@ForestLearn]

​@@charliecooper7458 Is the Durham physics dept ready for this many people with such a firm grasp of induction? 😂

[@peronazoro]

Hi, great video. I have a query though, when you say that by moving the wire up, the electrons are moving up so conventional current is downwards, why do you say it is just the electrons that are moving up? Aren't both electrons and protons moving up together, so wouldn't you be able to say that conventional current is also upwards since protons are moving upwards?

[@ForestLearn]

Hi, thanks for the interesting qn and apologies for the late response! Yes, if you focus on a proton, there is an associated upward conventional current, so in principle it experiences a magnetic force too. However, this is feeble in comparison to the strong nuclear force responsible for nuclear binding. Which is why we don't talk about it!

[@sadkayyy]

I've read that when the electrons in the wire accumlulate as shown in 2:50, they form an electric field which eventually becomes large enough to provide an electric force that balances the magnetic force, causing the electrons to stop moving, which in turn forms a potential difference. Apparently, by using magnetic force = electric force, magnetic force = BQv and electric force = QE = QV/d, the equation in 4:23 can be derived. What does this electric field look like, and how does it provide an electric force that acts opposite to the magnetic force? Also, is all of this just a really roundabout way of phrasing what you've mentioned in 2:50?

[@ForestLearn]

Thanks for your question! The derivation you mention is covered by me in this vid (and addresses your queries): kzbin.info/www/bejne/bn3Fh3ltnbh2jck Hopefully, this should clear things up - if not, let me know and I'll be happy to help :)

[@mujtabaalikhan8701]

Thank you so much, you have all qualities to teach any topic

[@ForestLearn]

Thanks for the kind words :)

[@444unknownuser]

youre acc the best

[@ForestLearn]

You're way too kind :)

[@phoebeli4999]

Thanks for separating the induction into three types! That is really helpful for understanding.☺️ btw is that means the hall voltage is actually an induced voltage of type I(the ‘cutting field lines’)?

[@ForestLearn]

My pleasure :) The Hall effect/voltage appears similar to type I induced emfs (both involve the magnetic or Lorentz force for their explanation), but try not to mix them up. In the Hall effect, the conductor is stationary and doesn't 'cut field lines' - we don't refer to the Hall voltage as an induced emf. Induced emfs are reserved for induction phenomena. Hope this helps!

[@beanbean9019]

Dude, your videos are so good keep up the great work!! :D

[@ForestLearn]

Thanks for watching and the kind comment :)

[@aphysicist9558]

The way I understand it is that from the perspective of the wire the flux changes as it moves through. The number of magnetic flux lines the wire 'counts' would vary as the wire cuts through. The closer to 90° the wire is the more this varies. When the wire is parallel to the field lines there would be no change in the number of field lines the wire 'counts'. Hence the emf induced is zero.

[@ForestLearn]

Try not to mix up the concepts of magnetic flux and magnetic field lines - they are different concepts. With a tricky topic like this it helps to be precise with terminology! People often talk about the 'number of field lines' etc., but this doesn't quite accurately reflect the true mathematical nature of the magnetic field. It's best to stick to simple, unambiguous physical reasoning as I've tried to present in this video.

[@AhmedKhaleelAhmedAhmed]

thank yoou

[@ForestLearn]

You are welcome :)

[@olegviatkin5674]

Great content👍

[@ForestLearn]

Thanks for the kind words :)

[@ramens]

thanks

[@ForestLearn]

My pleasure :)

[@KD_elctrcL_N_elctrnX]

Can the equation for this be derived from e=-dq/dt ?

[@ForestLearn]

Hi, thanks for your question and sorry for the extremely late reply. I'm not sure which equation you're referring to there, did you mean I = dq/dt where I is current? As I mentioned in video, the proof of Faraday's law can be found in this 'one marker' video: kzbin.info/www/bejne/bn3Fh3ltnbh2jck

[@antonferrara6605]

I remember reading about this in the chat physics article you wrote. An electron in the wire is moving upwards with the whole wire. This is effectively electron flow so conventional current can be considered in the opposite direction. Then using Flemming's LH law find the direction these electrons would experience a force in the wire itself. So is this the magnetic or Lorentz force you wrote about? As a result of the EMF induced by this force wouldn't it result in the flow of electrons in the opposite direction to the direction it originally moved or am I over thinking this?

[@ForestLearn]

Yes, Fleming's LH law/rule enables one to find the magnetic/Lorentz force acting on a charged particle (electrons in our example). This force is what moves the electrons along the length of the wire, and so the induced EMF develops across the length of the wire, not in the vertical direction as you seem to suggest.

[@nickstoebe2226]

Does cutting lines of flux induce voltage across normally not current producing magnets?

[@ForestLearn]

Thanks for your question! Moving a conductor (pink rod in video) so that it 'cuts across' magnetic field lines will induce an emf across the ends of the conductor (avoid talking about induced voltage in EM induction). Not sure if this answers your question? I don't quite get what you mean by 'normally not current producing magnets'. All that the magnets are doing here (labelled with north and south poles) is providing a magnetic field. At no point is there any current being induced or 'produced' in the magnets. Let me know if you want further clarification.

[@bharatankushe4271]

Sir in DC generator in which rectangular coil rotates in uniform magnetic field this is which type of induction cutting flux or change in flux I am confused because some one says coil cuts the flux and some one says flux linked with coil changes which one is true

[@ForestLearn]

Great question: both statements are true. We can analyse what's going on by either thinking of the coil 'cutting the field lines' or the flux changing in the coil/loop. Both points of view lead to the same conclusion (i.e. it is possible to derive the induced emf formula from either point of view). If you have seen the intro to induction video in the playlist, you will know that I talk of 3 different types of induction. What we are discussing here is an example of Type 3 ('the overlap') - situations which can be interpreted as either Type 1 or Type 2. I will be making videos on Type 3 in the near future.

[@ashe.8590]

Many thanks

[@ForestLearn]

Thanks for watching, hope you found it useful :)

[@tahabashir9405]

damn the british. They ruled us till 1947, take valuable foreign exchange amouting to Rs 42 billion (120052506 pound sterling) every year for the CIE exams, and even their explanations are better.

[@ForestLearn]

:|

[@bharatankushe4271]

Sir in alternator their is cutting filed or change in flux

[@ForestLearn]

I think this is a question? Alternators (AC generators) come in different varieties, and depending on the exact nature, can be an instance of 'cutting field lines' or 'flux changes'. I'll be putting up videos on alternators soon. Thanks for watching.

[@kashingngai5587]

Thank you

[@ForestLearn]

You're welcome :)

[@waelabdalmola9323]

Very useful 👌 Correct me if i am wrong The moment wire cuts field ,magnate made the wire to be temporarily magnetic too, when wire finishes passing the field , it goes normal again by moving e + in both the circuit or in the same wire itself.

[@ForestLearn]

Thanks for watching and your question! No, the wire does not become magnetic (or magnetised) at any point due to it 'cutting across field lines'. The key idea is that the wire's motion in the magnetic field results in a magnetic force acting on the electrons in the wire. This force is what's responsible for the induced emf that develops. I suggest you go through the video carefully again and try to follow the reasoning step by step (eg using Fleming's left hand rule). Hope this helps, but let me know if you have any further questions.

[@showdoctors]

Which metal is best for cutting the fileld lines.

[@ForestLearn]

I guess you mean in which metal would we get the highest induced current? That would depend on the properties of the conductor such as its resistivity.