Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Ohm's Law and series circuit

  1. Jan 28, 2004 #1
    In my physics lab we were asked a question for advanced studying. I read the chapter that it was supposed to be in, but I couldn't figure it out.

    Q: For a series circuit, what is the terminal voltage of a batter or power supply equal to in terms of the potential differences or voltage drops across circuit components?
  2. jcsd
  3. Jan 28, 2004 #2
    It's equal to the sum of the voltage drops.

    To rephrase the question: a battery of unknown voltage is connected to a series circuit containing three resistors. If the voltage drops across the resistors are 5 V, 2.5 V, and 1.5 V, what must the voltage of the battery be?

    The answer is 9 V.

    You can *kinda* create an anology between voltage for electric circuits and elevation for a water cycle: imagine the electrons in the circuit running 'downhill' through the various components. Resistors are like waterwheels mounted on vertical drops; they convert some of the 'height' (voltage) into heat energy.

    Batteries are like water towers; they come with one end full of electrons, and when all of those electrons have run 'down' to the other end, the battery is no good anymore. A DC transformer that you plug into the wall doesn't drain like a battery does cuz it's more of a vertical water pump than a tower. Of course, you can use a pump to refill a tower; that's a rechargable battery.

    Long explanation for a short answer. It's the sum of the voltages in the circuit.


    Attached Files:

  4. Jan 29, 2004 #3
    THanks, that makes a lot of sense. I guess I was just making the question harder than it actually was.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook