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Need a few details ironed out(right section?)

  1. Nov 4, 2011 #1
    I was going to post this in the homework section, but I wasn't a hundred percent sure where it would fit. I'm writing a paper over the 1893 World's Fair and the battle between Edison and Tesla/Westinghouse after the fair. I'm doing my orienting before I delve into my thesis statement and I'm a bit hazy on the details of the inner workings of DC power.

    I've looked on the internet and I can't seem to find a straight answer as to how it goes from generator to home. I need to be as accurate as possible, as this is a history paper, and if anyone has a link, or even some useful input, I'd appreciate it!
     
    Last edited: Nov 5, 2011
  2. jcsd
  3. Nov 5, 2011 #2
    AC and DC (for grid power) each have advantages and disadvantages. The main ones are:

    Its easier to generate AC than it is to generate DC. AC comes directly off the coils of a generator. You need rectifiers or switches (brushes) to convert it to DC. Also, if you use only the voltage from one coil and convert it to DC, it will still be pulsing DC. So you need to use a lot of coils where the pulses from the coils come at different times. That way if you combine the pulses from all the coils you end up with an almost smooth DC signal. But it still isn't perfectly smooth. You can smooth it further with capacitors, but high power applications would need massive and extremely expensive capacitors.

    When (non-pulsing) DC is sent through power lines, far less electromagnetic energy is radiated from the lines, which means less energy is wasted.

    Both AC and DC suffer from energy wasted because of the electrical resistance of the lines.

    Electrical power is proportional to the product of the current (electron flow) and voltage (electron pressure). If you use high voltage and low current, the resistive losses in a long transmission line are less. So Ideally you convert the electricity to high voltage and low current before you send it a long distance through wires, then convert it back to a more reasonable (safe and easy to manage) voltage at the load end. Conversion of AC is done with transformers. Converting DC in this way is profoundly more problematic.

    The simple voltage/current conversion is also very useful within appliances.

    Many appliances need DC. So the AC must be converted to DC. However, they typically need a certain DC voltage. Since conversion of DC voltage is more complicated (and costly when large power is involved) this is still a pro-AC argument, because converting AC of one voltage to AC of another voltage is easy (with a transformer) and converting low power AC to DC (for a household appliance, for example) is easy with a rectifier and small cheap capacitor.
     
    Last edited: Nov 5, 2011
  4. Nov 5, 2011 #3
    Thanks, Fleem, I really appreciate it!
     
  5. Nov 6, 2011 #4

    berkeman

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    Staff: Mentor

    Yeah, it's nice to have somebody do your homework for you, isn't it? :grumpy:
     
  6. Nov 6, 2011 #5
    No, he wasn't doing my homework for me. I've done extensive research for this paper and couldn't find anything that could lay it out in layman's terms for me. Actually, this subject has very little to do with the paper itself and has helped me with the last half of a paragraph in an 11 page paper. I don't mean to sound defensive, but I don't appreciate someone belittling the work I've done based on the fact that I couldn't understand a subject unrelated to my field of study.
     
  7. Nov 6, 2011 #6

    berkeman

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    The upset face icon was directed at fleem, who should know better than to provide so much help on a schoowork project. Perhaps that wasn't clear with my multiquote. I've moved this thread now to the Homework Help forums -- if it had been posted here originally (per the PF rules), perhaps fleem would not have provided so much of a solution in his try to be helpful.
     
  8. Nov 6, 2011 #7
    Ah, it looks as though I'm the one who has jumped to conclusions this time. Sorry about the misunderstanding.
     
  9. Nov 6, 2011 #8

    berkeman

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    No worries. It sounds like you did a good job on your paper. BTW, this thread helps to explain why the PF Homework Help rules are the way they are:

    https://www.physicsforums.com/showthread.php?t=373889

    Welcome to the PF!
     
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