The cheap Chinese bulb that won't turn off

alright let's turn this bulb off what a friend of mine called Mark Warner showed me the really strange behavior of some bulbs that he bought they're not your typical screw in Edison type bulb but they are fairly common what's strange about these bulbs is you can't turn them off like he's in his house and he flicks the switch and it stays on you see it's still glowing my first feeling was that I Wallis there's just a capacitor in there or something and you know if you give it time it'll eventually discharge and just you know it'll stop or maybe it's no that's not what's happening this will glow indefinitely how can that be well obviously I've managed to recreate the effect here in the lab so I thought I'd run you through what's happening like what's happening between this wire in this one and and why you might find that kind of scenario in someone's house step one the direct connection turns on is the connection turns off again there's no glow so here's what that looks like as a circuit diagram you've got this red wire coming out from live it's going through the bulb into the black wire which goes to neutral very straightforward I can make it all a bit safer by adding a fitting for the bulb and using these terminal block thingies look there you go the same thing happens and if I unplug it it goes off completely now just for fun let's add loads and loads of wires this is 50 meters of wire and I'm just gonna add it to the circuit I'm not going to change anything about it I'm just gonna make the wiring longer okay so let's follow the wiring the livewire comes out of here goes round and round around around around around around around around around around till it comes out the other end it comes around here stupid let's go straight back into there and that's the black way it's going round and round around around around running around comes all way back and now it's out here he goes through the bulb and then out through this black wire and back to neutral remember I haven't changed the circuit diagram at all I've just added loads and loads of wire to it that loops back on itself and it just so happens that the the loop of wire is kind of housed in this single casing predictably the bulb turns on there it is some of the unplug it it turns off the thing hasn't happened yet the next step is to break the circuit at this point by the way this is very very dangerous do not do this don't do this just don't do it's very dangerous we can just check that again so red wire comes out of here ran around around around around around stops there's a gap black wire ran around around around comes out here goes through the Bob goes to the moocher why the black one comes back to the plug plug it in and there it is there's that glow look at that but the circuits broken so how is it doing it what actually this is the type of wiring you end up with when you want to add a switch to your bulbs so wide in a wall switch and all this cabling here you can imagine that being in the walls and the ceiling of your house connecting the light switch to the light and of course when you turn it off it breaks the circuit but in this case the bulb stays on but the question is why well it turns out that all this cabling here is acting like a capacitor this capacitor isn't just storing charge from when the bulb was turned on and then slowly releasing it once it's turned off it's actually enabling the bulb to stay on permanently drawing power from the mains and costing you money the capacitor is just a component in a circuit you can push charge into by applying a voltage it can store charge and it typically looks a little bit like that how can a coil of wire act like a capacitor because when you think about electricity flowing through a wire you're thinking about the flow of electrons right and it's a bit like water flowing through a pipe that's a useful metaphor and when you apply a voltage to the end of a wire it's pushing on the electrons it's a bit like when you've got water in a pipe like this you can push on the electrons at one end and electrons will pop out at the other end like that right so long as the wire is connected to something but when the wires not connected to something like this when the circuit is broken it's a bit like me holding my finger over the end of this syringe it doesn't matter how hard i press it doesn't matter what voltage I apply I can't get the water to move because water is essentially incompressible and actually that's where this metaphor breaks down a better analogy in this scenario would be gas flowing through pipes so look I can stop the end with my finger which is like this end has been stopped here I can still compress the gas because gas is compressible and so when I put this thing in the the voltage here at the live wire this red wire is pushing electrons into the wire it's increasing the density of electrons and now the electrons outnumber the metal ions so there's a net negative charge built up inside this red wire all the way through this coil and you probably know this already electrons repel each other because like charges repel so all the electrons inside this black wire that's sat next to the red wire all the way through this coil are being repelled by the negative charge inside this red wire so to summarise the the voltage here pushes electrons into the red wire you've got a buildup of negative charge that negative charge repels the electrons in the black wire they're pushed out of the wire eventually out of here from the bulb which lights up into the neutral wire and then into the the neutral line of the mains now if Edison had won this wouldn't work if we were all using a DC power supply for our homes direct cone this wouldn't happen because think about it if you've got a permanent positive voltage here it will push electrons into the wire and the electrons will build up and build up in density until the repulsion of those electrons matches the voltage and you reach equilibrium no more current flows but Edison didn't win Tesla won and we all have AC power supplies in the homes alternating current so the voltage here at the the live wire is going up and down positive negative positive negative it's pushing the electrons in and then pulling them back out again repeatedly in the UK 50 times a second in the US 60 times a second and that's how you can have a permanently glowing bulb even when it's switched off so here's what the diagram really looks like that big coil of wire is actually a capacitor and I've only just thought about this the symbol for a capacitor is really appropriate because it's a break in the circuit this is an accidental capacitor but it's the same working principle in deliberate capacitors except that instead of having two wires you have two metal sheets maybe made of aluminium own minimum interesting so basically like aluminium foil and they're separated not by this rubber but by maybe wax paper and then the whole assembly is rolled up into a cylinder which is how you get the classic shape of a capacitor one thing that I really don't understand is why this only seems to work with these cheap LED bulbs from China and not the bog-standard LED bulbs that you might buy from a supermarket or a hardware store I've taken this one apart and the LED bit looks really similar but that there's a lot more going on with these components than there is in this one so all this stuff somehow prevents the glow maybe deliberately maybe by accident I'm not really qualified to figure that out but don't worry I know someone who is so to get the answer to this final part of the mystery you need to head over to a YouTube channel called electro boom if you haven't heard of electro boom already it's amazing you should subscribe to that channel but anyway for now I'll leave a link to the companion video over on his channel where he explains the difference between those things I'll put it in the car there up there in the corner I also put a link in the description and on the end screen as well but for now that is the story of the capacitor hidden inside the walls of your home I've got a big update about my regular sponsor brilliant dot-org they're offline courses functionality is now available on Android as well as iPhone that Android is superior to iPhone that's not contentious but one issue with Android was always that you couldn't use brilliant dogs offline courses functionality on that platform but now you can I use the London Underground a lot so it's a big deal for me I've been working through the Computer Sciences essentials course which is super interactive really fun and the ability to do that without signal or Wi-Fi down on the tube is great if you're not sure what course you want to dive into you should check out the daily challenges they're quick and really fun and every challenge has a full blown course attached to it if you want to dig a bit deeper a subscription gives you access to the full archive of daily challenges and to every single course so why not check it out today go to brilliant org forward slash Steve mold the links also in the description there and the first 200 people to use that link will get 20% off annual membership I hope you enjoyed this video if you did don't forget to hit subscribe and I'll see next time [Music]

Channel: Steve Mould

Views: 1,400,672

Rating: 4.7820482 out of 5

Keywords: explained, understand, electricity, electrons, lamp, light, capacitor, AC, DC, alternating current, direct current, wiring

Id: 1uEmX5XClPY

Length: 10min 27sec (627 seconds)

Published: Fri Jul 05 2019

Reddit Comments

[u/Double_Minimum]

This is what the weird led bulbs in my kitchen do, and oddly enough, during a home inspection for sale the issue came up, andI need to fix it. Weird that me changing the $5 bulbs is an issue worth bringing up, but easy enough...