hi like i said in my previous video i'll test the longest loop of wire in the history of mankind on youtube longer than the potassium's loop longer than alpha phoenix's lu to achieve greatness when you see it you go long long oh you don't know what this is about don't you watch my channel well the test case is from veritasium's video basically in his imaginary case we have a switch and battery connected to a bulb through zero resistance wires so long that it would take one second for electricity to travel the length of the loops at the speed of light but wires are one meter apart how long does it take for the light bulb to turn on after we close the switch his answer was since the wires are 1 meter apart only after 1 meter over c speed of light or around 3.3 nanoseconds there will be enough energy radiated to the other side to turn some lamps on which is right the electricity doesn't need to travel the full length of the loop before the lamp receives some energy right at the beginning so here i am with a thousand feet or almost 305 meters of cat5 ethernet cable and i'll test the theory with over 2.4 kilometers or 8 thousand feet of lube and i'll do it as ease in my room why should i stretch it straight over a vast field when i can do it as is in the comfort of my room you might say but maybe in derek's question the wires were spaced one meter apart chat five wires are like one millimeter apart it doesn't matter his wires were 300 000 kilometers long it doesn't matter chat five wires are twisted pair his wires were straight doesn't matter these wires were going in a straight line yours is looked like a transformer it doesn't matter well it seems my claims may have caused you to feel aroused then i bet you'll also enjoy my sponsor brilliant who with their highly interactive and well-designed courses in math computing and science are guaranteed to tickle your brain juice more at the end back to the test case let's try something so i have the thousand foot cable with four twisted pairs let's pick only one of the twisted pairs say the blue one and my test setup will be a little bit different see instead of two large loops like this i short one side and have one large loop on one side only but that's different it doesn't matter the reason it doesn't matter is if in the original setup it would take say one second for the electricity to travel through two loops to get to the load now it still takes one second but through one loop the load experiences a similar delay and the setup is simpler i'm using an led as the lamp connected to the loop of wire and i also have a dc power supply on one side connected to the led and on the other side i'll connect it to the twisted pair so how long do you think it will take from when i connect the power to when the led turns on well too quick and we won't be able to see so instead of shorting the end of the loop i'll leave it open now you're just changing everything it doesn't matter and the reason it doesn't matter is the entire theory here was that the electric fields from the sweet side take pico to nanoseconds to reach the led to turn it on long before the electric fields reach the end of the loop to discover if it is short or not so it doesn't matter at the beginning if the end is short or open now if i leave the loop open the led should stay off if our wave theory is wrong but if it blinks on and off the thor is right as we predicted the energy reaches the led before the waves reflect from the open circuit bringing the information back that the circuit is open and the led turns off with the end of the loop open let's see if it blinks just pay attention it might be too quick ready oh i think i saw it blink and it's not blinking anymore instead of a switch i'll connect a function generator with a pulse train to constantly turn it on and off maybe we can see it better now it'll shine nothing oh i know here i have a 10 kilo ohm resistor and i'll put it across the led and it turns on isn't it funny that adding a load across the led actually helps it okay the reason is simple an led is a diode and two wires being closed are acting like capacitors capacitors are how we model electric fields from one side affecting the other side so when we have a positive pulse current runs through the led turning it on and charging the voltage of the capacitance between the wires so when the pulse drops the diode is reversed bios and is off so there is no reverse current to discharge the capacitor and in the next pulse there is not enough voltage across the led to turn it on but we add a resistor across the led and the capacitor can discharge through the resistor when the pulse is low and in the next cycle the led can again turn on in any case again in veritasium setup the reason the lamp receives energy in 3.3 nanoseconds is that as current travels through the bottom wire and it becomes charged electric fields travel the gap and attract and pull opposite charges on the top wire creating current as i explained in my previous video we modeled this effect by placing capacitors between wires and also wire inductors as a transmission line charging these line capacitors is what sends current through the load and the line is seen as a resistor to the traveling waves now why do i claim my setup behaves the same as veritasium's test setup well of course some basic parameters would be different but the overall theory is the same veritasium wires were one meter apart and mine are like one millimeter apart it was an arbitrary number anyway so in my case the energy reaches the lamp faster the pairs being twisted doesn't change the coupling between them much so what instead of straight capacitors they turn like a string of dna which makes you ask in a straight line the capacitance is between two wires only but in a bundle like this all the loops are side by side and capacitively coupled or in terms of electric fields they don't need to travel like two kilometers anymore they just need to travel the length of this box for the energy to distribute over the wire no see this is why we have a twisted pair as we discussed as current flows one way in one wire it travels in the opposite direction in the other so we have what we call a differential pair where the signals are opposite when a twisted pair is placed close to another conductor the conductor distances alternate back and forth the positive wire sucks electrons and the negative wire repels them so the local currents in the adjacent conductor cancel each other and the twisted pair will have minimal effect on the adjacent conductors that's why having them in a bundle like this doesn't make a difference that's why we can communicate at high speeds over these cables no matter if they are straight or looped but then you might ask the looping wires create a transformer and the magnetic fields of one loop affects the other one no let's measure the inductance of one wire in a pair only these are the ends of a single thousand foot wire through all these loops and the measured inductance is 18.1 milli henry which is quite a lot and would easily filter high frequency now let's connect the end of the pair together basically we are putting two wires in series you would think two series inductances would mean double the total inductance or specially looped like this the total inductance could be closer to four times measuring the total inductance it's around 185 micro henry almost hundred times smaller than a single wire and this is the magic of a differential pair see self-inductance of a single wire is due to the fields formed around the wire in our setup though we are running two wires side by side with currents flowing in opposite directions so the fields that wrap around both wires run in opposite directions canceling each other which is great magnetic fields are killing each other and this reduces inductance same thing happens in veritasium's straight wires or a twisted pair that's why i can do the same veritasium test like this convinced then let's do it chat 5 has four pairs of twisted wire each wire is a thousand feet here so i have a total of eight thousand feet or over twenty four hundred meters of round trip but i have to connect them right every pair must connect in series to the next pair for the loop to work right if we randomly connect wires to create the loop we will get strange results because we will throw out everything i said about pairs the cat5 transmission line cable has a characteristic impedance of 100 ohms so to match it if instead of a lamp i place a 100 ohm resistor almost as soon as i close the switch the load will see half the supply voltage then after the waves travel the length of the wire hit the short circuit at the end and return the load voltage jumps to the supply voltage now i get to use my one gigahertz scope to see these fast transients and the longest loop of wire in existence in my room and instead of a switch i'll give it a 5 volt pulse train to turn the voltage on and off which i'll send through a driver circuit with almost zero ohm source resistance otherwise our function generator has a 50 ohm source resistance that can mess with our results we connect the supply to the loop and there we have it let's zoom in yellow is the supply voltage and green is the load voltage i was expecting a flat step at two and a half volt it does jump to two and a half volts but it drops and then it rises not even to the power supply it just sticks down there something broken oh i know see the 8 000 foot loop has around 220 something ohm resistance the model of the transmission line i showed was ignoring the wire resistance for shorter lines mine is long if we add those in these resistors will not let the line capacitances to charge easily and the voltage drops as the waves travel through the length of the line well we did test the longest loop and we can't get rid of the line resistance but let me show you something cool this spot is when the reflections of the waves from the end of the loop return to the load and make a change if i disconnect and reconnect the end of the loop you see the first 12 microseconds stays untouched i guess i could have used the one megahertz scope for this test so as we predicted the waves have to travel at the speed of light to the end of the loop and return to the load before the load knows that the end was shorted or open and with 12 microseconds over 8 000 feet we get the speed of light which is of course what they do got 203 million meters per second that's not 300 million meters per second that's two-thirds 66 percent of the speed of light what they do it is 8 000 pizzas right all right the speed of light is almost 300 million meters per second in vacuum it changes in different dielectric medium so here we see it drops to 66 percent in this cable good confirmation let's reduce the line resistance i'm gonna cut 40 meters of cable and only use a single pair for my loop the line resistance would be negligible and hopefully we can get a straight step 40 meters of twisted pair would be 80 meters of total loop length which would be 400 nanoseconds of wave round trip okay 40 meters of cable in a single pair i'm still using 100 ohm load resistance because the line characteristic impedance is not changed and the end of the loop is shorted and if we look at the load voltage we see it steps into two and a half volt middle of the five volt supply for around 400 nanoseconds and then steps to 5v supply well clearly my driver can't supply a sharp and clean input voltage to the circuit but you get the idea and again the load only knows if i've connected or disconnected the end of the loop after the waves travel the length of the loop at the speed of light through this medium beauty let's put a 50 ohm as the load let's see oh now it takes multiple steps for the load voltage to settle the waves keep reflecting from the ends of the loop you see the sharp edge of the step is getting wider as the pulse travels multiple times through the length of the cable and filters out and if we open the loop after the first step there are multiple steps before the voltage settles around zero let's try a 200 now the first step is more than half and the next steps overshoot and undershoot around the supply before they settle open close open close open well hopefully we learned a few things today such as my sponsor brilliant is a great place to learn from basic to professional level knowledge in math computing and science do i have to repeat myself you can sign up and start learning for free using my link brilliant.org electroboom then if you're not too late you might be among the first 200 people who'll get 20 off brilliant annual premium subscription and enjoy learning what you need for your job school or interview from some of the best interactive courses there i personally learn better when i can see how my actions change the outcome of something and that's how 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