Voltage and Current

Discussion in 'Homework Help' started by iflabs, Sep 14, 2006.

  1. iflabs

    Thread Starter New Member

    Sep 14, 2006
    6
    0
    I'm taking a course in circuit analysis and the terms "voltage" and "current" is really holding me back. I know definition of the terms but get easily confused when I try to imagine what actually is happening in a circuit.

    So lets get this staright, within a voltage source charges are seperated giving you the "+" and "-" terminals--which I would imagine to be a big electric field. What motivates the electrons to flow around the circuit? Is it the "-" terminal of the voltage source that the electrons want to reach when they are released from the "+" terminal? Will the electrons always be released from the "+" terminal of the voltage source?

    How exactly does a battery lose it's power? My guess is that the energy or electrons is lost through resistance and converted into heat, whilist a few electrons make it back to the battery. Does this mean that the voltage or electric field gets weaker in the battery when it gets drained, up to a point where there is none?
     
  2. slartybardfast

    New Member

    Aug 2, 2006
    2
    0
    The level you appear to be studying at would allow the old Water analogy.
    Have you ever watched the "Currrent" in a river?
    River current is measured by how many litres of water pass you a second. Electrical current is effectively how many electrons are passing some point in the cable a second.
    (strickly it is the number of Coulombs of charge per second)

    Voltage can be loosely related to water pressure. You can have all the pressure you like but the water wont flow until there is a path.
    Once you have a path for the water then you will get flow (current). The more pressure (voltage ) you maintain on the water the more flow (current ) you will get.

    Conventional current flows from positive to negative. Actual current flow (with electrons in a metal wire) flows from negative to positive.

    Cells and batteries generate electricity chemically. Once all the chemistry has occured then there can be no more electricity.

    Follow this for batteries.
    http://home.howstuffworks.com/battery.htm
     
  3. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    143
    slartybardfast's water analogy is by the far the easiest way of envisaging what is happening with respect to voltage and current in an electrical circuit. Remember that voltage is the potential force available to motivate electrons to flow as current.

    You may find it helpful to look at: http://www.allaboutcircuits.com/vol_1/chpt_1/4.html

    Dave
     
  4. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    I was taught that electrons flow from - to +. The - of the battery or ther power source supplies electrons and the + side draws them in.

    "Current" is defined as a flow of charge carriers. If the charge carriers are electrons, then current flow is from - to +. If the charge carriers are "holes," then current flows from + to -. Both are present in every circuit at the same time. Which one we choose to study is arbitrary; teacher and textbook usually decide on one or the other.

    A battery does not loose power (power being measured in Watts) but instead looses energy (energy being measured in Watt-hours). The energy is indeed converted from chemical energy into either heat, light, magnetism, motion, or some such.



    Metaphores:

    Voltage is a big kid (or two) pushing or pulling.

    Current is a big dog (or two) on a skate-board.

    Resistance is the surface over which the skate-board must move, whether ice (negligable resistance) or sucking mud (very high resistance) or something in-between.
     
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