in resister current reduses or voltage?

Discussion in 'General Electronics Chat' started by sabbi, Feb 25, 2010.

  1. sabbi

    Thread Starter New Member

    Feb 2, 2010
    in resister current reduses or voltage.
    1)if voltage drops how current remains constant.according to ohm's law current and voltage are directly proportionl to each other.And if both of them reduses then in series combination of resisters current through each resister remains same.:)
  2. Robert.Adams

    Active Member

    Feb 16, 2010
    Resistors have voltage drops across them. They essentially convert this voltage to current.

    Current remains constant because the voltage applied across the entire circuit does not change. For example, if you have a 9V connected to a 3k-ohm resistor and a 1k-ohm resistor in series, there is a total of 4k-ohm in the circuit with 9V across it. There is only one branch for the current to go through and that current can be found with ohms law: I=E/R=9/4k=2.25mA

    Each resistor drops a different fraction of the total voltage. Since E=IR, and I=2.25mA and you know the resistances, you can find:
    E(across 3k) = 2.25mA*3k=6.75V
    E(across 1k) = 2.25mA*1k=2.25V

    The resistors dissipate the energy as heat. I hope I covered your questions, but I'm not sure if I'm even reading half of your post right. Please be more precise in your questions.
  3. leewillz


    Jan 11, 2009
    just to add to roberts post, with resistors in series you can pick specific values to give a ratio of the voltage for example if you have a 12v supply and you want maybe 9v out then you would put a 10k and a 20k resistor in series because they are at a ratio of 2:1 there will be double the voltage across the 20k than the 10 so in between both resistors you will have 9v, because the resistors share the load out equally. not really in the context of the question but still useful to know about resistors.
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
    Perhaps a picture will help. Look at the simulation. R2 is fixed at 99Ω. It is in series with a varying resistance. The plots show the current, the voltage across R1 and R2 as R1 is varied from 1Ω to 999Ω. Note that the sum of the voltage across R1 and the voltage across R2 must add up to 10V, the battery voltage. Note that the voltage across both R1 and R2 is proportional to the Loop Current. Note the algebraic solution in the schematic...
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  5. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    Think of Current as Flow, like flow of water.

    A resistor restricts flow, like a partly-closed tap does water.

    If there is no current, the voltage is the same at both ends of the resistor.
    If you double the resistance of the overall circuit, the current is halved for that supply voltage. If you then double the supply voltage, you get back to the same current.

    And one of the most basic rules; in a series circuit at steady state, the current is the same at all points. (If a certain flow goes in one end, it must be the same all the way through and come out the other end.)