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Basic Circuit Flow

  1. Aug 26, 2009 #1
    Hey guys, i'm having a little trouble understanding the flow of electricity on PCB's and basic circuits. I understand what capacitors and resistors are intended for, but I don't understand thier application. On most designes, there are multiple paths electricity can flow after it leaves a capacitor or resistor. How do you know where the current goes when it has multiple paths to choose?

    Is it possible someone can walk me through a very basic circuit design with a capacitor or resistor and maybe a LED light or something. I've looked for tutorials and books at borders on this stuff and can't seem to find anything basic. I've decided just to try and reverse engineer what others have designed instead :)

    Any help is much appreciated!
     
  2. jcsd
  3. Aug 26, 2009 #2
    I don`t know if this may help but if you think of a circuit the same way as you think of a water piping system it may help.

    Basically current is lazy and it always wants to flow through the path of least resistant. That is why if you have a load in parallel with a shortciruit all the current flows through the short circuit ( because of the theoretical 0 resistant).

    I don`t know if this help in anyway or even provides any type of incite into your question. However, i hope it does.
     
  4. Aug 26, 2009 #3

    negitron

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    Current follows all possible paths with more of the current following paths with low impedance and less following paths with higher impedance. Consider three resistors in parallel, 1 ohm, 10 ohms and 100 ohms with 10 volts applied across them. Through the 1-ohm resistor, a current of 10/1=10 amps flows; through the 10-ohm resistor, a current of 10/10=1 amp flows and through the 100-ohm, you have 10/100 = .1 amps. The total current is therefore 10+1+.1=11.1 amps. Of course, this is a simplistic example, but you apply these same basic principles to any circuit.
     
  5. Aug 26, 2009 #4

    negitron

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    People need to stop saying this because it's not an accurate statement and ends up confusing the issue. Current follows ALL possible paths. How much current flows through a given path depends on its impedance and the voltage across it.
     
  6. Aug 26, 2009 #5
    Well this is the theoretical explanation given in most textbooks. Do you agree with the example i gave in my previous post ?

    You yourself pointed out that... `more of the current following paths with low impedance and less following paths with higher impedance. `` which is analogous to what i said.

    I agree with you that current flows through all possible path... that is why we have current flowing through resistors regardless of their magnitude.

    When i said current flows through the path of least resistant i didn`t imply that it doesn`t flow through other paths. :)
     
  7. Aug 26, 2009 #6

    berkeman

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    Staff: Mentor

    I'm glad that you clarified what you said, it can be confusing to folks just learning about circuits. The all-paths statement is a better teaching device, IMO.

    Welcome to the PF, BTW.
     
  8. Aug 26, 2009 #7
    Yportne,

    In my opinon, you should lay off the capacitance for a while and chill out with Ohm's law and Kirchoff's circuit laws until you feel better.
     
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