| Electronics > Beginners |
| Some noob questions |
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| Terry01:
I think you've got it the paddy way round buddy. Volts=power current=flow of volts. Current is the flow of volts and volts is the potential energy between 2 points. Think about filling a sink with a hose(current) the water(volts) then filling a paddling pool with the same hose(current). You'd crank the tap up more when filling the pool compared to the sink but the hose/"current" stays the same but the water(volts) is more powerful. It'll click soon :) |
| bsudbrink:
Absolutely, the analogy is very rough. But it is a starting point. To go to a real world example, you have probably seen a Van De Graaff generator. It can make sparks that "jump" through several centimeters of air. If you have ever "taken a hit" from one, you know it hurts but generally it won't kill you. They let kids play with them in science museums (with supervision). On the other hand, most vacuum tube (valve) devices have voltages and currents inside them that can easily kill but they are constructed inside of grounded metal cases with small clearances and no sparks fly. The Van De Graaff generator is very high voltage and almost no amperage. The valve device is much lower voltage but much higher current. |
| Mr D:
@Terry: i've read quite a few times that voltage absolutely doesn't flow. But you're talking a flow of volts. ??? |
| PA4TIM:
You forget the resistance of the load. There are voltage sources and current sources. If you feed a lamp with 1A from a current source the voltage will be as high as needed to "push" one amp through the resistance of the lamp. If the lamp is 10 ohm the voltage will be 10V. If the lamp is 20 ohm the voltage will be 20V. The source runs out of steam (voltage) if the resistance becomes so high it needs more volt as the source can deliver the current drops. Just Ohms law. If you use a voltage source and you set the voltage at 50V, the current through the 10 ohm lamp will be 5A and through the 20 ohm amp it will be 2,5A The wall wart thing is a voltage source. The load (the lamp, a resistor, motor, circuit) will draw the amount of current it needs and as the source it can deliver things are fine. 'If the load draws more current as the voltage source can deliver the voltage drops. Again Ohms law. And then there is power. The current times the voltage. Don't get to attached to the flowing electrons story. ;) |
| rstofer:
--- Quote from: Mr D on July 16, 2018, 08:52:12 pm --- Also, does the analogy break down in the sense that in the water example, the diameter of the pipe is also key, but in the metal wire, this i less important? --- End quote --- If I want to push a lot of current through a wire, it will need to be larger than if I want to just push a few milliamps. Wire has a property of Ohms per 1000 feet (usually). So, I divide the resistance by 1000 to get Ohms per foot and maybe again by 12 to get Ohms per inch. Now that I know the resistance, I can calculate the voltage drop for any current I want. There are standards like 1000 amps per square inch of cross section for substation bus bar but that's a side issue. Voltage dropped in wire is usually a waste of voltage and creates heat (voltage drop times current given in watts). I don't want heating (usually) so I use a bigger conductor if this gets out of hand. --- Quote --- I'm not trying to be argumentative, just trying trying to understand. I've heard a few different variations of the water analogy, but it only gets me so far! And how would you describe "power" in the water analogy? --- End quote --- If we take power as volts (pressure) times amps (gallons per minute) I suppose we can find some units that will ultimately make sense and it will be "Fluid Power" measured in HP after applying a constant. http://web.applied.com/assets/attachments/779D4407-D2AE-6FAA-7DA1CEDE2268977B.pdf 3rd table entry... Where the water analogy comes unglued is with inductance. It sort of works ok for capacitance but, basically, we only use the analogy for voltage, resistance and amps. It is just a crutch to give people an intuitive sense of what is happening. It is talked about for the first half hour of the first lecture on DC circuits and never mentioned again. |
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