| Electronics > Beginners |
| On a 250V capacitor or a CRT, is the negative terminal -250V? |
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| Brumby:
--- Quote from: Starglider on May 31, 2019, 05:52:35 am --- --- Quote from: Ysjoelfir on May 31, 2019, 05:49:46 am ---(Noticed that you guys were much faster than me.... but hey, never the less this could be another way to see it :) ) If you short circuit any charge holding device, let it be a capacitor, a battery or your CRT, you basically introduce a second element into the equation: A resistor. If you use a screwdriver to short out the energy container, like it is often done with CRTs, or if you just use a plain piece of wire, this resistor is very, very small. Never the less it is there and closes the circuit. Since - as you/the 10-year-old already noted - energy can't escape (=can't evaporate into nothing), we have to find a way for the energy to "get out" of the energy container and to the surrounding world, leaving the container empty. This is where said resistor comes into the game. Energy can't be destroyed but it can be changed into another form of energy, in this example the energy is converted by the resistor into heat. If you use a smaller resistor you can absolutely feel it heating up. If you use the screwdriver or a jumper wire you can't feel it - just because the thermal mass of those "resistors" are so massively huge that the converted energy just doesn't affect your "resistor" in any noticeable way - except to the points where you touched the capacitor: you will most likely see and hear some sparks while touching (because of the high resistance of the insulating air, potential dirt, grease,... on the "resistor" in the moment very very close to the point of it making contact) and see some black burnmarks = produced heat. And that is, where your stored energy went :) --- End quote --- Funny, I asked someone else that and they said that the Sparks were just a side effects. I specifically asked if the 250 volts was being converted into heat and light and dissipating into The ether and was told no. So I guess that is correct after all? does the full 250 volts disappear as a spark? This assumes that there was 250 volts sitting inside the CRT to begin with, which I know is unlikely after you hit the power especially if it's there is a discharge resistor on the flyback transformer. --- End quote --- The energy held by that charge will get dissipated into heat energy, some electromagnetic radiation - which includes the light from the spark - and some mechanical deformation which is the pit created by the spark. The end result of all this will eventually turn into heat. |
| Starglider:
Alright guys that's all great. Let the lesson begin! |
| radiolistener:
--- Quote from: Starglider on May 31, 2019, 02:48:36 am ---• +250V on the positive plate/terminal • -250V on the negative Or is it 0V on the negative? --- End quote --- Voltage exists between two leads. This is electric potential difference. So, if there is 250V on the capacitor, the right way to say 250V. In order to say 0V, there is need two leads and electric potential difference 0V between these leads. |
| radiolistener:
--- Quote from: Starglider on May 31, 2019, 04:13:32 am ---"if the capacitor is like a bucket, when the bucket is full why does touching metal across both handles make the bucket empty?" --- End quote --- water will be a bad analogy because it almost cannot be compressed. Technicaly electricity is like gas (for example air). The difference between gas and electricity is that gas consists of molecules and electricity consists of charged particles (for example electrons). This electron-gas can circulate inside metal, but almost cannot leave it. In order to leave metal, there is need very high pressure for electron-gas, because air or empty space are isolators - they like glass for usual gas. When electron gas leaves metal you can see it as electric lightning. Then you can imagine two glass vessels connected by a hose. When air pressure in both vessels are equals, there is no gas movement in the hose and this is equivalent for 0V voltage between two leads. Then attach the pump into the hose break and pump air from one vessel to another. You will have pressure difference between two vessels. This is equivalent for electric potential between two leads. Higher pressure difference between vessels is equivalent for higher voltage between leads. Now your capacitor equivalent is charged. You can replace pump on the hose with air valve. If you open valve, gas will starts to move from vessel with high pressure into vessel with low pressure. This is equivalent for electric current flow. Electric current in the metals is represented by free electrons (negative charged particle). These electrons moving from "-" lead to "+" lead. It happens because there is excess electrons on the "-" lead and lack of electrons on the "+" lead. When count of electrons on "-" lead and "+" lead will be equal, the electric current will be stopped. It means that your capacitor is discharged and now has 0V potential difference between leads. Vessels volume is equivalent for capacitor capacitance. Higher volume vessels can accumulate more air molecules. Higher capacitance capacitor can accumulate more electrons. This is how electricity works in classic metal. In salt water electric current flow works in a little different way, it consist of positive particles - ions. Ion is an atom or molecule with missing electron. Since it consists of proton which has positive charge and this proton charge is not balanced with electron pair, it has total positive charge. The difference between metal and salt water is that metal has free electrons, which can flow between atoms, but cannot leave metal. And water has ions (proton charge is NOT balanced with electrons), which can flow between normal atoms (proton charge is balanced with electrons), but cannot leave water. When electrons moving in the metal, it can randomly crash into atom, so the atom starts to moving, it leads to thermal loss. This is why metal is heating when electric current flows through it. The same thing happens in the air hose when it has some kind of air obstruction, when high pressure air flows through this air obstruction, it heating it. In some cases it is possible to make condition for ordered motion of electrons with no collide with atoms. This is known as superconductor effect. There is no thermal loss in such case. AC electric current is equivalent to rapid pumping of air from one vessel to another and back with high speed. It leads to cyclic air flow through hose back and forth. This air flow can be used for some useful work. :) |
| Starglider:
Would you guys say the simplified layman's explanation given at 4 minutes into this video is a good one for giving a basic understanding to non engineers? https://youtu.be/a6FMpvs71pc The video owns that it is a simplified explanation. The energy being converted into the light and heat of a spark, so going into the atmosphere and therefore not needing to go into a ground cable? Makes sense but is it correct? |
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