what if i connect wire to only one terminal?!

Discussion in 'General Electronics Chat' started by buffon2009, Sep 12, 2014.

  1. buffon2009

    Thread Starter New Member

    Dec 7, 2011
    28
    0
    hello everybody

    i get a lot confused about this problem

    if i have a wire not connected to anything and there's an varying electric field suppose this field of an radio channel

    there will be currrent through the wire

    if i connect one terminal of wire to the negative terminal of battery

    the current from elecrric field will stop or no effect on the current?!

    please answer me with a little physics explain as you can
     
  2. profbuxton

    Member

    Feb 21, 2014
    233
    68
    If you have an unconnected wire it will do nothing!
    If you connect the wire to a battery( one end only) it will do nothing!
    If you connect one end of the wire to Mother(or Daddy Earth or Ground or the soil under your feet) it may act as an aerial ( depending on what varying electric field are around) and a teeny current may flow. Depends on wire length and other factors. This is now a very basic radio aerial.

    If you connect the wire to the negative battery terminal ( or Positive, you choose) only NO current will flow through the wire. If you now connect the other end of the wire to the other terminal at the same time a current will flow because you will have completed a CIRCUIT and provided a current path from positive to negative(or vice versa).

    Depending on battery size,state of charge, wire size and length you may or may not experience a nice flash and melt the wire or just glow for a bit or it will just discharge the battery
     
  3. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    Minute curents will flow, as the charges are redistributed within the wire in response to the electric fields, but, as profbuxton says, we do not normally consider current in this situation as the currents are not sustained. No charge carriers will enter or leave the wire, so there will be no current into or out of the wire.

    This is really a potential (voltage) issue.

    A static electric field applied to the wire will cause redistribution (separation) of charge within the wire until the field due to the separated charge is exactly equal on oposite to the applied field.
    At this time the minute internal currents cease.
    If the applied field now changes then new charge residstribution occurs, so if the field is continually changing minute currents are continually flowing in response.

    The effect of connecting to a battery terminal will be no different from any other source of electric field. The battery has a constant field of V/d volts per metre where V is the battery voltage and d is the separation of the terminals.
    So this field will add to the other field. But it should be remembered that the electric field is a vector quantity so the addition is vectorial.
     
    Last edited: Sep 12, 2014
  4. buffon2009

    Thread Starter New Member

    Dec 7, 2011
    28
    0
    thanks profbuxton and studiot for your answer

    i asked this question because i tried to use a coaxial cable as antenna when i connect the shield to the negative terminal of battery the received signal is more perfect than make shield unconnected

    the shield is a conductor and there's an varying electrical fields and when leave it unconnected the received signal is bad , when connect it to the negative terminal of battery of the device the received signal is perfect why ?!!!! !

    i got confused please help me understand that
     
  5. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    You would need to describe you setup more fully.

    What battery are you talking about?
    Is it the battery in the receiver?

    How are you connecting the core of the coax to your receiver?

    What other connections/grounding do you have in place?
     
  6. profbuxton

    Member

    Feb 21, 2014
    233
    68
    Please clarify your statement re "connect it to the negative terminal of the device". What "device" are you talking about? How are you connecting the coax. You started by asking about a wire connected to a battery negative now you are talking about a coax cable connected to a "device".
    Please show details of just what it is you are connecting and how.
     
  7. buffon2009

    Thread Starter New Member

    Dec 7, 2011
    28
    0
    the coaxial cable consist of inner and sheild which both are conductors

    i put coaxial cable in a high level up the roof of the home

    at the other end onnthe receiver device there's a plug in which you connect antenna which consist of two terminals
    the first one i connect the inner and the second one i connect the shield

    the second already connected through device into negative terminal of the battery
     
  8. profbuxton

    Member

    Feb 21, 2014
    233
    68
    I think I understand what you mean. You are connecting a coax cable over some unknown distance to the terminals of a "receiver" which has the"second" terminal connected to the negative of the battery.
    If you do not connect the shield of the coax to the "second" terminal then you have length of "unshielded" coax which will act as a "aerial" for any stray fields along the its length and you will have a "noisy" signal.
    When you connect the shield to the negative terminal you provide "shielding" from EM "noise" and a path for any "noise" to conduct via the shield to a common ground on your "device".
    This is very a very basic concept of use of shielded cabling of any sort for audio or rf signals.
     
  9. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    Yes I agree
     
Loading...