Intro to Electromagnetic Waves (how EM waves are created, Poynting vector)

How electromagnetic (EM) waves are produced, and the relationship between their electric and magnetic components. Plus how to find the direction of propagation using the Poynting vector.
0:00 - Intro, quick review of mechanical waves
0:39 - How EM waves are created in an antenna
2:14 - Magnetic field component
4:44 - The whole picture
5:21 - The Poynting vector (finding direction of wave travel)
7:02 - EM Waves from antenna simulation

[@gamelord5798]

Excellent simple explanation of what is usually presented in a convoluted complex manner. This is the essence of good teaching.

[@livehopeskul1157]

Excellent explanation. I really understand electromagnetic wave now

[@tech-savant]

Explaining EM waves with gang signs, great video

[@sanjayrshinde]

Excellent explanation. Thank you. Keep up the good work.

[@Pedritox0953]

Great explanation !

[@shaker1144]

Great explanation. Thank you

[@Pratim_Ganguly]

Now after going through your channel my expression is like why didn't i find this channel earlier? Please keep uploading topicwise physics videos.

[@mehdimoussavi]

you answered some of my important que, thank you master

[@aaditya7547]

Thank you for the video, it was a great explanation.

[@IntelR]

That's a pretty cool video man!

[@akhilaravind3741]

Thank you..nice video

[@nickharrison3748]

Good explanation

[@aprfff1]

Fantastic!

[@spandana5326]

beautiful!

[@bitmineern6322]

Are you kidding me!? Thats was the best drawing!

[@LucasRenanTech]

awesome 10/10

[@williamwalker39]

A recent radio experiment showing light propagates instantaneously in the nearfield and reduces to the speed of light in the farfield, after one wavelength is also another discovery that will radically change our understanding of science, in particular all of modern physics. In this experiment,the time delay of signals was measured between 2 dipole antennas as the antennas were separated from the nearfield to the farfield. The results showed that the radio waves (light) propagates instantaneously in the nearfield and reduces to the speed of light in the farfield after one wavelength. This corresponds to not only the phase speed and group speed, but also the information speed. These results are completely incompatible with Special Relativity, which is based on the speed of light being a constant c. Inserting c=infinity into the Lorentz transformation yields Galilean transformations, where space and time are absolute. This shows that if an inertial moving object is observed using instantaneous nearfield light, then no time dilation , length contraction, or simultaneity Relativistic effects will be observed. So if Relativistic effects are observed using farfield speed c light, then by simply flicking a switch, one can change the frequency of the light, such that instantaneous light used instead, and the effects of Relativity would go away. This shows that the effects of Relativity are just an optical illusion and that Galilean Relativity is the correct form of Relativity. Here is another very powerful argument that shows Relativity is based on a logical fallacy. According to Relativity, observers on a moving train and on a stationary train platform will disagree on the size of the ""Train"" and the passage of time on the ""Train"". This is a complete logical contradiction if the size and the passage of time of the train are real. If the size of the train is real, then the ""Train"" can not be both contracted and not contracted. The same goes for the observed passage of time on the ""Train"". If these effects are observed, then the only possible conclusion is that it is an optical illusion. Things that are real must appear to be same from all frames of reference. If not, then by definition it is an illusion. Again the argument is very simple and it is the argument Einstein used to derive Relativity, and no acceleration is used in the argument. A train with length (L) traveling at constant velocity (v) relative a stationary observer on a station platform. According to Relativity, the stationary observer will see the train contracted (L/r, where r is the Relativistic gamma), whereas an observer on the train will see it not contracted (L). So the train is both contracted (L/r) and not contracted (L) depending on the observer. This is a complete contradiction (L not equal L/r) and can not be true if length is real. The same argument applies to passage of time on the Train, where both observers will disagree on the passage of time. If time is real, it can not be both dilated and not dilated (T not equal rT). If space and time are observed to be both large and small simultaneously for one inertial reference frame, such as the ""Train"", then it must be an optical illusion. It should be noted that experiments proving Relativity can only give evidence that the theory may be true, but an experiment disproving Relativity, or a logical proof showing a logical fallacy in the theory can absolutely disprove the theory. I have provided both. Since General Relativity is based on Special Relativity, General Relativity must also be an optical illusion. Spacetime is flat and gravity must be a propagating field. Researchers have shown that in the weak field limit, which is what we only observe, General Relativity reduces to Gravitoelectromagnetism, which shows gravity can be modeled as 4 Maxwell equations similar in form to those for electromagnetic fields, yielding Electric and Magnetic components of gravity. This theory explains all gravitational effects as well as the instantaneous nearfield and speed of light farfield propagating fields. So gravity is a propagating field that can finally be quantized enabling the unification of gravity and quantum mechanics. The current interpretation of quantum mechanics makes no sense, involving particles that are not real until measured, and in a fuzzy superposition of states. On the other hand, the Pilot Wave interpretation of Quantum Mechanics makes makes much more sense, which says particles are always real with real positions and velocities. The particles also interact with an energetic quantum field that permeates all of space, forming a pilot wave that guides the particle. This simpler deterministic explanation explains all known quantum phenomena. The only problem is that the Pilot Wave is known to interact instantaneously with all other particles, and this is completely incompatible with Relativity, but is compatible with Galilean Relativity. But because of the evidence presented here, this is no longer a problem, and elevates the Pilot Interpretation to our best explanation of Quantum Mechanics. *KZbin presentation of above argument: kzbin.info/www/bejne/qZazlX1tq7iErLM *Paper it is based on: William D. Walker and Dag Stranneby, A New Interpretation of Relativity, 2023: vixra.org/abs/2309.0145

[@mukhtaarjamaac4698]

I understand it All thank today is great day to me

[@amaellediop8260]

Exactly what I was looking for; I got lost in all the rules and formulas, just needed a logical explanation.

[@nomabey]

10/10

[@nikan4now]

Thanks for the video. I have a question: Through what mechanism do the waves propogate? I get how at one point you'd get the osculating fields but I don't see what maes the fields move forward. Is this predicted by the math?

[@mdrakibulislam8643]

You can think of it as feeding water in a pipe from a pump. Here the pipe is the medium(vacuum, air, water, etc..), and the RF transmitter is a motor. As the transmitter keeps feeding, the energy keeps radiating out. Notably, the free space (Vaccum) works exactly like a transmission line to the EM wave with a characteristic impedance of 377 ohms.

[@tonytea6279]

This is why KZbin is such a boon for education. Someone brought up the Poynting vector the other day and I told them to hit up YT. I teach electrical power system theory, and in every lesson I source random explanations to inject variety into my delivery. Tell me, does the Poynting vector, etc. invalidate the water analogy of pressure/flow/opposition?

[@PhysicsOMG]

It depends on what level of physics you're teaching. The water analogy works when students are starting out learning about DC circuits because it gives them something they can relate to, but once you start talking about AC circuits and the fields in a circuit you can't really use it anymore. But at that point they will have some experience hopefully and understand what is happening without having to use analogies.

[@ismagine]

This is a hot topic due to the latest Veritasium video!

[@ifrazali3052]

I wish you also had add self sustaining quality of EM waves

[@kwadwonyaledzigbor4778]

What carries this electromagnetic field away from the generating current to far distances?

[@hamidtehrani9919]

Do you have a large LED acrylic board to write on? Your technique for teaching is interesting

[@PhysicsOMG]

yep, it's an acrylic sheet with LED edge lighting

[@numbr6]

This explanation is very close to answering my original question: How does AC power move from a generator 300mi away down a transmission line if the electrons are just "moving back and forth"? The answer lies in a moving charge creates an EM field that propagates down a wire to the transmission lines. An AC generator and a radio transmitter really are doing the same thing: creating EM fields. When a radio "wave" leaves the antenna, there is no "going back", that wave has left the antenna. Same for a generator and a transmission line. Nearly all explanations miss this point, or get bogged down in their original miseducation on this topic. A generator is really a "transmitter" operating at 60Hz. A 80m Ham rig is a transmitter operating in the 3.5MHz-ish range. No one questions where does the oscillating RF field go, clearly down the transmission line (coax ususally) to the antenna. Then that RF field is radiated into free space, possibly directionally, or omnidirectional. Clearly that "+/-, -/+, +/-, ..." charge is not just "going back and forth" in the coax. It seems all explanations about moving charges totally miss this key concept captured by this video.

[@DrDeuteron]

When the charge separation is maximum (peak |E|), the current is zero (B=0). When current is maximum (peak |B|), the charges have minimum separation (E=0). So, based on that, E and B are out of phase. The wave has E and B in-phase. Explain.

[@PhysicsOMG]

Dipole antennas are not as simple as they seem, but thats the example our textbook uses. This example we use assumes you are looking at the waves after they have propagated far enough away from the antenna so that they are plane waves. Near the antenna they are out of phase, but from Maxwell's equations when you look at the relationship between E and B fields one is a time derivative and one is a spatial derivative, and when you solve for a plane wave they are in phase.

[@MasterBho]

Hi, this will probably clear your intuition: When E has its peak, the current is 0, from maxwell equations, this implies that the curl of B is 0. However, this does not always imply that B is zero, in this case it’s actually the other way around: curl of B being zero means that B does not change much when taking a tiny steps towards any direction Taking as an example the 2 dimensional case, you have ∂B/∂x=0, and that only happens when B does not depend on x (is costant everywhere in space) or, as in this case, when it is at its peak (when functions depend from x they hit their peak value when their derivative is zero, this is a common result shown in analysis), and that’s what actually happens in the case shown, where both E and B are in phase (As a sidenote, we already know B is not costant in space because of the propagation which happened beforehand) Similarly, when E=0 ∂E/∂x as its peak, which implies from maxwell equations that curl B has its peak, which in turn implies B changes a lot when taking a tiny step (∂B/∂x maximum value). That only happens when B changes completly orientation, when his value is B=0 so again, in phase

[@petevenuti7355]

Is that what is meant by near and far field? And if propagation is in every direction .mmm.. Photon?

[@peterszekely7490]

What you say is based on Ampere's law which has limitations and doesn't work in every scenario (for example this one). Try its extended version, the Ampere-Maxwell law and it will make sense.

[@josephdavis7487]

Can you explain how near field change into far field so that e and b fields are in phase, I have spent lot of my time to find answer to this question with out any sucess

[@akildoktoru]

I watched tens of videos on this topic, but I still cannot animate in my mind how E and B fields interact to form a self propogating wave. For example look at half of a wave at 3:14. I can see that the source charge (or current) going up and down creates the blue E lines. I also take for granted that each blue line creates a perpendicular pink magnetic line. But then when and how pink B lines create which blue E lines (as modelled in Maxwells equations) as a part of this self propogation?

[@rob7469]

Ampere's law says that whenever electrons move, a magnetic wave (B) is produced. Faraday's law says that whenever a magnetic wave is changing(such as the antennae example in the video), an electric field(E) that moves electrons is produced. These two laws of electrodynamics are the push-pull of what creates a self-propagating electromagnetic wave(in a vacuum).

[@rajeshchandrasekharan3436]

Can a square wave of high frequency creat EM waves?

[@MehrTV.]

What is the nature of the electromagnetic field?

[@simongross3122]

Thanks for the video. You said that electromagnetic waves don't require a medium. How do we know this is true? Is it simply the case that we have never detected the medium and therefore assume that it doesn't exist?

[@PhysicsOMG]

Scientists used to think there was an "ether" that was the medium for EM waves, but the Michelson-Morley experiment showed that there was no ether detected. I suppose that doesn't mean that it is disproved, but everything we know so far shows no sign of EM waves needing any medium.

[@youngtreebig1]

Thanks! But why the direction of current is opposite to the direction of electric field?

[@mohammedwajith1416]

conventional current is defined as the rate of flow of positive charge through a cross-section

[@PhysicsOMG]

Current is the flow of negatively charged electrons. Since field lines point in the direction that a positive charge would feel a force, they are opposite for electrons

[@gamelord5798]

Okay, now explain to me how dipoles and ions react in these fields. :-D

[@scientist23wannabe_23]

Can i ask something why does the electric field travel

[@PhysicsOMG]

It is similar to why a wave in water propagates out when you disturb a point on the waters surface, the change in the electric and magnetic fields at one point induce a change in the part next to it

[@scientist23wannabe_23]

@@PhysicsOMG thank you so much sir. They never tell us at school

[@geofferyromany4634]

Nice intro. Headache less now.

[@philoso377]

Nice video and presentation. A plate capacitor without permittivity between its plates cannot establish polarized electric field inside to store charge. Permittivity is provided by dielectric materials such as glass, ceramic, gas as well as vacuum. The permittivity in vacuum is responsible for polarized electric field inside, also responsible for alternating polarized electric field in vacuum and hence electromagnetic and light wave, in vacuum. That also explain why we can see distant stars millions light years away, through vacuum. Vacuum permittivity is provided by Aether, a light medium.

[@paulnothnagel2136]

Not flipping but more like a phasor e^jwt rotating