Why does WATER change the speed of electricity?

in my last video about electricity the thumbnail asked the question does electricity travel at the speed of light and i got a lot of comments that said no of course not because electrons have mass and wires have resistance so electricity can't travel at the speed of light now the conclusion that i arrive at in that video is that electricity does travel at the speed of light or it's at least so close to the speed of light that for all intents and purposes you can just use c to calculate it but based on all those questions about resistance of wire today i'm gonna test that so in my effort to be like the strangest neighbor possible i have spent the last few days well i set it up the first time like six months ago but i have set up a huge loop of wire in my front yard and the same electronic setup that i used in my last video to time how long it takes electricity to go around this loop but i don't just have one loop of wire i have three loops of wire with different resistances different thicknesses of wire we're gonna see if there's a difference [Music] this is almost the same setup that i used in the previous video the obvious difference being that there's only one loop of wire in the previous video i had a loop going out from the battery and switch in both directions and then approaching the resistor or the light bulb that was the load and one of those loops really didn't matter so i've removed it the other really big change i guess really small change i don't know is that the loop isn't 500 meters anymore it's only 12 meters because it needs to fit in my front yard the whole timing setup and how it looks on the oscilloscope should be exactly the same the way this is wired actually didn't have to make it exactly the same i could have used a simpler setup but for the sake of comparison it's identical and we can still see the delays very clearly on the oscilloscope so let me show you how that works so the big loop of wire that extends all the way out there through the front yard comes back to this circuit so i have this electronic switch here and when this switch is open as in before we have flipped the switch and started to flow current through the loop it's basically holding the entire loop at about one volt potential now the actual amount of charge in a wire is in my mind the best analog for voltage that you can come up with it's not perfect because it changes with the local capacitance of the wires and stuff like that but basically when this circuit applies a volt to the whole wire it's depleting that wire of electrons i actually made an attempt to measure how many electrons i was removing from the wire and got an answer somewhere in the realm of two or three hundred million electrons now that sounds like a lot of electrons it's a lot of particles but if you look at the number of free electrons that are in the wire that's actually less than a quadrillionth of the free electrons in the wire so it doesn't really seem like very much but it actually is and i'll talk more about that later when this switch closes it launches a whole bunch of electrons all at once into this alligator clip which then start that wave propagation thing and when that wave goes all the way around the loop and comes back then current starts flowing through this resistor and we can measure that on the scope if you saw the last video this graph is not going to surprise you the x-axis here is time and the y-axis is voltage and we're looking at a variety of signals within the circuit the yellow trace is the switch so when this trace goes from low to high that is when we've actually flipped the switch we've launched our pulse of electricity into the circuit the white trace is the voltage at the other end of the loop so this is the signal that has gone all the way through the loop and come back that we have to wait for and if you actually go look and see how far this is we can measure in time that's uh let's get it right there yeah that's almost 100 nanoseconds that's 98 nanoseconds so it takes electricity 98 nanoseconds to go through that loop when we send this pulse into the loop 98 nanoseconds we get this pulse back out the other end so i know that the loop of wire out there is exactly 28 meters long because i measured it earlier but before you actually get to the scope probes where the measurement is made there's an alligator clip on both sides so that will add 40 centimeters on each end so if i take 28.8 meters and divide it by 98 nanoseconds we get 2.939 meters per second that is almost c 98 the speed of light so in the last video i guess i didn't know exactly how long the wire was so i couldn't make this calculation but here i can say that the speed of electricity is 98 of c in this configuration that i've got right now using the 2.4 ohm magnet wire now i also have a thinner magnet wire with a total resistance of 6.3 ohms across the entire loop and that wire has the exact same enamel coating on it as the wire that i just tested so it should have the same dielectric properties and we should get the exact same speed despite the fact that it's a significantly different resistance so with the new wire hooked up that cursor is still right on the money we have not changed the propagation speed one bit 98 nanoseconds it is fun when physics works cool but wait there's more i also have thicker wire so it's some of this stuff soldered together into you know a big 28 meter loop and this is actually multi-stranded wire and because it's so much larger across the entire loop it only has a resistance of 0.9 ohms so it's a much lower resistance case i would expect that as bare wire this would propagate the electric signal at exactly the same speed as the magnet wire that i just tested the only thing that could throw a wrench in that is that this is not enameled wire it's got this thick like rubber insulation on the outside which is going to have a slightly different dielectric effect and could end up slowing the signal down just a tiny little bit we'll see i'm very curious i also want to point out that although it shouldn't matter one bit i am actually only hanging one of these wires at a time i'm suspending it off the ground in order to keep it away from the wires that i'm not using i just have the other ones laying out here you know a solid half a meter away so they should have no impact on the experiment but i knew that if i didn't say that people would ask as i'm tripping through one of the smaller wires thick wire is all hooked up moment of truth is it still going through the loop at the same speed maybe i might call that a little bit longer maybe 99 nanoseconds or maybe maybe 100 nanoseconds it didn't change very much but all for the for the sake of argument here i'll call this a hundred i need six percent the speed of light three wires three different resistances the exact same propagation speed really within measurement error on all of them and all of them are just about the speed of light in a vacuum which is just about the speed of light in air which just so happens to be the thing that's surrounding these wires so if the resistance of the wire doesn't change the speed at which electricity moves through that wire what does to answer that question we really need to understand how electrons push on each other through a wire as a quick refresher let's think about what's happening in this wire at the subatomic scale when the switch is flipped the electron density in the wire is a little bit below average earlier i mentioned that we only actually removed a half of the quadrillion of the electrons that are able to move in the wire but for the sake of clarity in this diagram i've removed a quarter of the electrons when we flip the switch all of a sudden we dump a bunch of electrons into one end of the wire these electrons want to spread out and make the whole wire neutral again but they don't spread out like this they spread out like this where each electron just moves a tiny bit until they're all evenly spaced again now in actuality if you want a steady state current to flow in the wire you can't actually let the wire reach equilibrium the electrons want to spread out and make the whole wire neutral but if the battery keeps pumping electrons into one end of the wire then they never have time to fully spread out this means that in steady state electrons are actually slightly denser right in front of the negative end of the battery and slightly less dense right in front of the positive end of the battery because electrons are charged particles every single electron emanates from it an electric field this is something that is inherent to the particle like you can't have an electron and not have it make an electric field other charged particles are acted upon by this field however the moment we flip the switch and dump all these extra electrons into the end of the wire the next electrons in the wire don't start moving right away they need to sense the field of the electrons inside the switch and this field doesn't travel instantly it travels at the speed of light once this electron scoots forward a bit it's now emitting its own field from a slightly different place but the next electron again doesn't know that yet and has to wait for the field to update at the speed of light before it scoots forward updates its field and so on the signal we just measured the speed of electricity is not the speed that an electron moves through the wire it's the time that it takes for an electric field to reach an electron and for that electron to respond by twitching imperceptibly forward in the wire so that it can in turn apply a tiny force to the next and this wave of motion happens very quickly so if you want to slow down electricity you want to slow down the propagation the rate at which electrons can shove each other through a wire you have to limit the electrons ability to interact the fields that they use to talk to each other you've got to find a way to slow that down and because most of that field is moving outside of the metal wire you've got to actually change the speed at which fields propagate outside of the conductor now maxwell has something to say about this the actual equation that defines the classical speed of light depends on two variables that describe how whatever substance that light is passing through responds to both electric and magnetic fields which means that if we surround the wire with a material that strongly interacts with electric fields we should be able to slow down light and therefore electricity so i am about to try to change the speed of electricity i'm not 100 sure that it's going to work i'm hoping that this big pipe once i fill it with water is actually going to slow down the propagation of electricity in the wire that's running through the middle of that pipe i think this is going to work because water is a very strong dielectric now dielectrics are substances which are insulating meaning that they can't have electric currents passed through them you're not going to get electrons to flow all the way through like a brick of plastic but dielectrics are polarizable meaning that they can actually generate a small electric field specifically when you put a dielectric in an electric field that dielectric material will create its own opposite electric field that partially cancels out the original electric field and this decrease in intensity of the field comes along with a decrease in propagation speed which means that the signal that has to go through that loop should take longer to go through that loop after i fill that tube with water what am i looking at yes it moved it a tiny little bit check that out it worked okay so we went from 45.6 nanoseconds to about 50.6 calculating the slowdown here is surprisingly non-trivial because only a portion of the signal should be slower plus my initial timing without the water already showed a slightly slower result than the bare wire but i didn't know that yet because i actually filmed this experiment first but whatever okay so i just rechecked my math and the actual slowdown of the electricity passing through that pipe was between 1.4 and 1.5 x that means that the speed of electricity flowing through that pipe was approximately two-thirds the speed of light in a vacuum we would expect that the speed of propagation of an electric field through a large body of water would be about nine times slower than the speed of propagation of an electric field in air or vacuum but that's not what we saw when i ran electricity through that pipe full of water it actually only slowed down the propagation of electricity through that wire by about 1.45 times that's not nine all matter is going to interact with an electric field just because it has an electron cloud around a nucleus if you had a water molecule and you all of a sudden applied an electric field to that molecule the electron clouds around each nucleus would sort of shift just the tiniest little bit in order to cancel out part of that electric field this has the effect of decreasing the amplitude of the electric field and slowing down the propagation of the electric field if you let that water molecule sit in the electric field and cook for a while it will eventually orient itself like literally rotate the entire molecule to align with the electric field so now let me come at this from the other end of the spectrum quite literally the index of refraction of water is about 1.33 that is the expected slowdown of light like optical frequency radiation passing through water so if we just predicted that water was going to slow down the propagation of electric field by 9x but light which is just an oscillating electric field is only slowed down by 1.33 x what gives turns out that the slowdown you expect is frequency dependent so if you have that water molecule and you apply an electric field that sort of slight rearrangement of the electron cloud that happens like instantly almost instantly because the distances are so tiny and the amount of stuff that has to move is so tiny that just happens next the whole molecule starts to rotate but that happens really really slowly now once that molecule rotates it has a really significant impact on the field because of this we can say that very very high frequency electric fields like light that you can see is going to interact with water molecules very weakly and very slow electric fields that are going to stay at one polarity for a really long time before flipping and gives the water molecule time to react and time to cancel that field those frequencies of electric fields are actually going to interact with water more strongly so the cool thing here is that we have shown that flipping a switch is actually closer in frequency space to light than it is to just having a steady state dc field which is weird because we're just flipping a switch it's dc that's what's happening right here this is the signal that i'm actually i'm this is literally the signal being fed into that wire right now and you can see that we're just you know at one voltage and then it changes to a different voltage also i want to point out that this equation i gave earlier for the speed of light in terms of the materials permeability and permittivity is very specific it's the equation for the phase velocity of electromagnetic waves derived as these perfect smooth planar sine waves and this does not look like this and the discrepancy here is very important imagine that this slope right here was actually part of a sine wave i want to say because that's literally what it is it's literally part of a sine wave but that's it feels sort of disingenuous but sort of not because the physics works with sine waves so you can take any signal and decompose it into sine waves it's called a fourier transform and there are oodles of fantastic fantastic videos about fourier transforms and how to take an fft computationally in order to see all the frequency components that make up a signal i'm not going to get into that in detail right now but i'll direct you there's probably i'll make a three blue one brown video i'm sure that there's a great three blue one brown video about ffts i've probably watched it but for right now imagine that this signal right here is actually made of a whole bunch of sine waves added together so the way that i have this scope configured right now it can actually show us all the frequencies that are making up this step the trick is that i have to show it a bunch of steps you have to flip that switch on and off and on and off and on and off a whole bunch of times in order to give the scope enough data to properly decompose this step into a whole bunch of sine waves so i'm just going to zoom out and you can see that we're turning it on and off and on and off all the time these are our frequency components this is an fft which means that on the x-axis you have frequency think of every point along the x-axis is a sine wave a signal that could exist in this wire with a slightly different frequency and anywhere that this graph peaks that means that that frequency is basically present that if you take a sine wave of this frequency and a sine wave of this frequency and a sine wave of this frequency and a sine wave of this frequency and you all of them all of these peaks and you add them all together then you'll get that shape that you'll get this switch on characteristic where we're flat and then we ramp really quick and then we're flat all of the equations that we use in physics to govern the propagation of fields are much simpler and rely on the fact that these fields are going to be like sinusoidally varying that you have some sort of regular oscillating signal it just makes the math work so a signal like this could be construed as the sum of a lot of independent signals that all by themselves are propagating through that wire and only when you add all of those signals together does it actually give you the shape and give you the reality of the situation that we're just flipping a switch when we're assuming that the field passing through the water is you know a nice sinusoidal continuously varying thing why can't we say that the water in that pipe is reacting to all of the individual frequencies that actually make up this signal that's the kicker so in the last video i had a lot of questions that were talking about ac versus dc like okay so you're flipping a switch on and you're using direct current to you know put us push a signal down the wire and then the signal comes back down the other wire the answer is that it's all ac the act of flipping a switch actually has frequency components all of these frequencies of signals are occurring at the same time and adding together but look at how many different frequencies we need in order to actually see this switch on characteristic the act of flipping a switch is ac like you are changing an electric field you're changing the current flowing through the wire these are really fast frequencies that electric field that is associated with like one of these spike sine waves is going really fast which is why it seems like we're closer to light than we are to a static electric field which is just so cool so after all of these tests we see that the speed of electricity has less to do with the wire and more to do with the speed at which electrons communicate with each other and since this happens at the speed of light in order to change the speed of electricity we have to locally change the speed of light by filling space with some material that interacts strongly with electromagnetic fields because the speed of light in that material is going to be different than speed of light in something like air or vacuum the really freaky thing is that light of different frequencies travels at different speeds in different media and the question that always really kicks around in my mind is whether or not reality is actually made of all of these simultaneously occurring waves that you know coalesce into something that looks like it makes sense to us or whether this set of waves everywhere is just how our very human mathematics makes sense of the world i really like the westworld line if you can't tell the difference does it really matter but in this case i think that a physicist might say if it produces the same observable it's an equally valid wave function that's way too corny of a line to end on so i guess in this video i talked about how resistance doesn't actually affect the speed of electricity but in the next video i'm going to talk about what resistance does affect and that's the speed of electrons so i'll see you then [Music] you

Channel: AlphaPhoenix

Views: 735,854

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Id: rQIg5XeIgQ0

Length: 24min 25sec (1465 seconds)

Published: Tue Sep 06 2022