Thanks, that did help more.
My (again, layperson’s) understanding is that AC is required/preferred for electrical motors? What other applications is AC more useful than DC for (other than stepping up/down its current)?
Also, isn’t there a “no-current” moment in the waveform of DC as well? I’d probably do well to just do a class in physics than annoy you but… i’m in the office, so I’m gonna annoy you 
I’m not at all an electrician, but I don’t think DC has a waveform. It’s just a continuous flow, like water through a hose. AC is more like pushing the water a little way down the hose, then pulling it the same distance back up the hose again, 50 or 60 times a second.
PhasmaFelis is correct. We’re oversimplifying this, but the voltage of what we’re calling AC is typically a sine wave whereas DC would be a constant voltage – pushing and then pulling in alternation, versus just pushing, is a decent analogy.
The biggest advantage of AC is that, because its strength is continuously varying, running it through a coil produces a varying magnetic field… which can then produce a varying current in another coil. That’s the principle a transformer works on – by having more or fewer loops in one coil or the other you can step the voltage up or down (while stepping the available current down or up inversely). To step voltage up with DC, you would need a motor/generator pair, which is bulkier and less efficient and more prone to wear and so on… or you’d need to convert it to AC and then convert it back. AC is thus easier to distribute – you can use high-tension (high-voltage) lines for long runs at (relatively) low current, and then step it down to a more practical voltage when it reaches the neighborhood, then step it down again for consumer use, just by putting it through appropriate transformers.
(There are ways other than transformers to step DC down – switching power supplies do that – but that’s more complicated and hard to do for substantial amounts of power.)
Motors can be designed to run on either AC or DC; there are advantages and disadvantages to either design depending on what kinds of power/torque you need (and what electrical supplies you have available). It’s been long enough since I had much reason to look at that in detail that I’m going to refer you to the web.
See also Wikipedia’s description of the “War Of Currents” for additional descriptive information on advantages/disadvantages of each.
There are good reasons AC won for power distribution. There are good reasons most of your home electronics internally converts it to DC.
Cool cool, thanks. Wish I cared more about this stuff in school cause it would be handy to know now.
So, to put a final plug in my bathtub of lacking knowledge, when people graph DC like this:
what are they graphing?
This is actually sort of a tricky question. Could a computer be designed to operate with AC? Sure (for example, I could imagine making switches out of magamps). But the current designs that use MOSFETs wouldn’t allow it. I started to write a detailed explanation on how a transistor switch works, but I realized that it would be thousands of words and require a lot of drawings. But the short answer would be that when you operate a transistor as a switch, you need to have some base conditions for when the switch is ‘ON’ or ‘OFF’. For a MOSFET, you have some DC voltage rating that is guaranteed to turn the switch ‘ON’, some DC voltage rating that is guaranteed to turn the switch ‘OFF’, and an intermediate range that you can’t operate in (undefined behavior). And for the sake of not adding to confusion, be sure to note that the switch itself does not determine its output. It is how it is wired. For example, a light switch in the ‘ON’ position will not turn ‘ON’ a lamp if its input (the plug to the wall) is ‘OFF’, the breaker (another switch) is ‘OFF’, or your power line grounded. A microprocessor is built out of complicated switches, but the actual operation of a switch can come from the output of another switch. In this way, logical gates can be constructed. If you want to learn more, study transistor switches (not amplifiers). It is amazing how much complexity can exist in something as simple as a switch.
want.
matrix.
learning.
There’s too much friggin’ stuff to learn! Thanks for your help though, I do have a better grasp of these things now than I did this morning (but if the apocalypse comes, bags not reinventing electronics!)
That’s a graph of rectified AC. It can be put through a filter and/or regulator stage to average it out into a (reasonably) constant voltage, which would be more properly described as DC… but without that filter you’d have to qualify it as “pulsating DC”, which is not an uncommon term but it is a misleading one unless you ALWAYS use the qualifier.
In general, if it isn’t a reasonably constant voltage (modulo batteries running down), don’t call it DC.
Well, yeah, you could build a computer out of relays too, and those could operate off AC. Much less compactly, and much more slowly.
If you want ICs that pack as much logic onto a chip as humanly possible, a single-transistor NAND gate, and a flip-flop memory cell that needs only two or three transistors, is going to be Really Hard to beat until we get to practical quantum computing or something else that completely replaces our most basic designs.
(BTW, it’s nice to see someone ask a question and actually want an answer. Now if only we could make some of the nontechnical discussions work that way.)
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