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Electric Circuits

  1. May 3, 2007 #1
    For a single resistor in a circuit all of the voltage is lost across that one resistor. But when there is more than one resistor in the circuit (in series or otherwise) the voltage is distributed according to the resistance of each resistor. Why is it that all of the voltage is not lost over the first resistor in this circumstance? How does it know not to lose all of its voltage across the first resistor and keep some for the other one?

    Thanks for any help.
     
  2. jcsd
  3. May 4, 2007 #2
    What makes the current circulate in a resistor is the voltage between its terminals. This current, as you know is V/R. As the current in all parts of a series circuit is the same, the voltages will be proportional to the resistances values.
     
  4. May 6, 2007 #3

    Claude Bile

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    The extra resistors result in less current. Because there is less current flowing through the initial resistor, there is a smaller voltage drop across it, as per Ohms Law.

    This is just a more circular way of saying what lpfr posted.

    Claude.
     
  5. May 8, 2007 #4

    chroot

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    The bottom line: it's the continuity equation that says that current must be constant everywhere in the circuit.

    - Warren
     
  6. May 13, 2007 #5
    Umm... Here's an easy way to devise this.

    You're right in the assumption that one resistor will take all voltage. So we have ways of changing 3 diff resistances into one resistance.

    Resistors in series (the current doesn't split) will simply be added (IE: 3 ohms + 6 ohms = 9 ohms total resistance).

    Resistors in parallel (the current gets SPLIT) will be added inversely (IE: 3 ohms, 6 ohms: 1/3 + 1/6 = 1/Rtotal... 3/6 = 1/Rtotal... 2 ohms total resistance.)

    After converting it all into one resistance, we simply use V = IRtotal, solve for I to determine the current across all resistors in series, for example.. Then the 'voltage drop' across each seperate resistor is simply Itotal*Resistor value (or Vdrop = IR),

    Wish I could draw this for you, but you get the idea.

    And chroot, I hate to admit, is wrong :-p Current is not constant for all circuts, only for series circuits containing just batteries and resistors.

    Capacitors, Inductors, and parallel circuits all affect current.
     
  7. May 13, 2007 #6

    chroot

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    You mean, current.

    This is only true if you've only taken one circuits class and don't know what a phasor is. Keep learning.

    - Warren
     
  8. May 13, 2007 #7
    For that, I did mean the voltage loss. He's right in his statement
    So what I was elaborating was that you can reduce almost any simple circuit diagram into a battery and a resistor and simply go on from there and work your way backwards.

    I'm not even in college yet, phasors aren't exactly delved into at an AP Physics C course, but at least we cover them ;-)

    I've done phasors... Somewhat fun, but the videos on them are very... 'intriguing' :-p

    You're talking about Z, impedance (sp?) right? Yeah, it's one of those real-world applications thing between imaginary and reality :-p While I've done them, I choose to reject that reality at the moment until I go more in depth on them.

    But I see your point on phasors and current.
     
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