1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Cell EMF

  1. Oct 2, 2007 #1
    just a simple question, why is it that in almost all circuits where a battery is the source of DC , the EMF is considered to be constant over time while in reality is it not ? The EMF is a decreasing function w.r.t time considering the battery is operating.
  2. jcsd
  3. Oct 2, 2007 #2


    User Avatar

    Staff: Mentor

    It's just a simplification that works for many purposes. It definitely does not work if you are doing the circuit design, though....

    Welcome to the PF, BTW.
  4. Oct 2, 2007 #3
    Also, residential AC voltage commonly varies some 20 volts (~6%) in most of the US depending on demand (not to mention fluctuations due to surges). What one can count on with the former is the accuracy of frequency.
  5. Oct 3, 2007 #4
    Thanks to both of you.

    berkeman, so I understand that this is for purely theoretical purposes. I ask because my purpose is building a battery and then testing it in a simple circuit. So the more accurate results, the better.

    Loren Booda, now that you've mentioned AC , I am curious about its multi-direction flow of electrons. I have read that somewhere, and I think it means electrons move forward or backward unlike in DC ciruits where electrons flow in one direction , correct ? If this is so , why does it occur ?

  6. Oct 3, 2007 #5
    Alternating current may be understood more accurately as an electric field alternating, i. e., moving back and forth, through a wire - although the alternating electron (particle) picture is mostly correct. The main advantage with AC is that it may be transformed down from high voltage, having fewer losses in transmission. The generator which creates AC inherently converts relatively circular motion between magnets and coils into alternating current.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook