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Know the total resistance of the whole circuit

  1. May 12, 2005 #1
    please feel free to move this thread as i cannot find the correct place.

    in a series (dc), when two bulb of the same resistance is used, the two bulbs lighted up as bright. when one bulb is used instead of two, the bulb ligth up brighter.

    if again, two bulb arrange in circuit, why not the bulb nearrer to the negative end light up brighter then the next one. it seems that the electron already know the total resistance of the whole circuit at the first bulb to decide the amount of energy relesed at the bulb.

    am i messing up some where???
  2. jcsd
  3. May 12, 2005 #2


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    Staff: Mentor

    A circuit can only have one amperage just as a river can only have one flowrate. Tossing a massive rock into a river doesn't make the rest of the river instantly "know" the flowrate has changed, there is a short delay as the flow through the entire river adjusts to the change, starting at the point where the change was made. Same goes for electricity: if you suddenly attached a second light, the circuit would not react instantly to the change.
  4. May 12, 2005 #3
    It would react pretty quick though!!!
  5. May 14, 2005 #4
    by using water, for example the brightness of the lamp is equal to the erosion of rock.

    in the first place, when there is a boulder at the high land, it slows down current after the river or decreasing it's volume. and so when there is another boulder at the low land, it wont be eroded as much as the high land as it already lost it's energy.

    a bad example actuallly, but i couldnt find a better one.
  6. May 14, 2005 #5
    If the river flows at the same rate all the way along (as current does in a circuit) the rock erosion would be identical everywhere!!
  7. May 18, 2005 #6
    no, i meant that it flow slower down stream as the energy had been used upstream
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