Why are resistors useful?

  1. I don't understand why we use resistors at all. I've read that they cause a voltage drop and decrease the flow of electrons (current). Why is this useful? If we want to decrease the current, why not just lower the voltage? Don't resistors just waste energy?
     
  2. jcsd
  3. And how will you lower the voltage at different points in a circuit?.
     
  4. So it's only because the same voltage supply is used for different "things" (that require different currents to flow through them)?

    Do you mean if R<1? So.. a resistor can increase the current?
     
  5. Yes the main use of resistors is voltage control and current control.
    http://en.wikipedia.org/wiki/Current_divider
    http://en.wikipedia.org/wiki/Voltage_divider

    The current always decreases with increasing R. What I meant was that it would be very hard to adjust the current in a low resistance circuit just by adjusting the voltage. I edited that out because It might be confusing and maybe not a very useful way to think about it.
     
  6. rock.freak667

    rock.freak667 6,228
    Homework Helper

    Resistors are also useful in generating heat. For a current I through a resistance R, the powerloss is P = I2R which manifests itself through heat (this is how circuits overheat and stop working or burn). Using this idea, you can use this heat in applications such as light bulbs, electric stoves, soldering irons and so on.
     
  7. A perfect circuit would encounter zero resistance. Love to see somebody build it. You would be a trillionaire. Power my AC with no resistance LOL
     
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