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How do I reduce the amount of voltage in a circuit?

  1. Mar 13, 2015 #1

    I'm having a difficult time understanding how voltage is reduced in a circuit. I know the relationship of V= IR, but I still don't understand. I think part of the reason I do not understand is the wording used, and the other part is from experience. For example if I have a fan that only works properly at 5 volts applying more than 5 volts could damage the component, right? Would I use resistors to reduce the voltage? I thought that resistors only changed the current in the circuit. When I have measured the voltage by placing one lead of a multimeter on a resistor and one lead on the power output I didn't see a change in voltage, only current. By changing the current in a circuit do you simultaneously effect the voltage as well? Also I'm quite puzzled over the analogy of water going through a pipe being used to describe voltage, current, and resistance. It seems to me that it is more like water going through a filter in a straw being blown on by a person's mouth. In this case the harder you blow is like the voltage or pressure and the amount being blown by a point is like the amps and the resistance is like the size of the filter. Is this a good analogy?

    Thanks in advance for helping me answer these puzzling questions.
  2. jcsd
  3. Mar 13, 2015 #2

    Doug Huffman

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    Resistors drop voltage E=IR
  4. Mar 13, 2015 #3


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    that's only part of the story

    the real problem using a resistor to drop voltage is that it will limit the current. And it may limit it to less than what is required by the load

    So @Broly tell us more specifically about what you are trying to achieve, so we don't have to keep guessing :wink:

    You have a 5V fan, and Im assuming ( till you explain otherwise) that you only have a higher voltage PSU ?
    Voltage regulator chips are the best way to overcome this problem

  5. Mar 13, 2015 #4
    Water in a closed system of pipes is an excellent analogy for current in a circuit. The pressure between two points in the pipe is equivalent to voltage. It's the relative pressure between two points that matters, just as it's the voltage between two points in a circit that matters. Pressure goes up across a pump, just as voltage does across a battery or generator. And pressure goes down across a thin section of pipe, just as voltage is dropped across a resistor.

    The flow rate, in say gallons per minute, is equivalent to current, in coulombs per second (amps).

    I used to be embarrassed that even after decades of work, I still think in terms of water in a pipe to keep it all straight. But recently I read that none other than James Maxwell thought of electric fields as whirling vortices to help him keep things straight.
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