easiest..

Discussion in 'General Electronics Chat' started by speeed_777, Feb 20, 2009.

  1. speeed_777

    Thread Starter Active Member

    Oct 5, 2008
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    I think question ,I am going to ask is very easiest,yet I don't know:
    why there is a sparkling when we directly connect two wires of any supply (i.e. positive,negative for D.C. battery)?
     
  2. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    2,039
    287

    Greetings:

    Sparking is caused by ionization of the air when the conductors are very close. The voltage GRADIENT increases dramatically JUST before contact.

    Contacts that do not spark have large radius geometry, avoiding sharp points. This distributes the charge evenly so there is no sudden voltage gradient at any point.

    Switches operated in a high vacuum don't arc because there's no air to ionize.

    eric
     
  3. speeed_777

    Thread Starter Active Member

    Oct 5, 2008
    54
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    yes that's right. In case of A.C. voltage there is a blast with such a connection or breaking of fuses. why?
     
  4. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    2,039
    287
    Because once air ionizes, it suddenly changes from a good insulator to a good conductor! You have to break the air "wire" once an arc starts!

    eric
     
  5. speeed_777

    Thread Starter Active Member

    Oct 5, 2008
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    thanx,But I am still confused..
    yesterday,by mistake i directly shorted out two main A.C. supply wires and unfortunatley, I have not join any fuses also,and I lost my mobile charger..which is ON at that time .why?
     
    Last edited: Feb 20, 2009
  6. b.shahvir

    Active Member

    Jan 6, 2009
    444
    0
    Dear Alex, :)


    The question posed by you may be easiest….. but answering it can be a tedious affair!.... still I will give it a go.

    The conducting wires of any supply is supposed to have a much lower resistance than the load on the wires. Current thru the wires is inversely proportional to resistance, voltage remaining the same. In other words, theoretically if the wire resistances become ‘zero’ the current thru the wire becomes ‘infinite’. This however can never happen in real life as the current is always limited by supply wire resistance…. but is still very large.

    Coming to your sparking question; as both wires directly come very close together, while attempting to short ckt. them….. heavy short circuit current flows thru the contact resistance between the 2 supply wires which, as yet, are not properly electrically connected! This large current thru contact resistance causes heating of air molecules surrounding the contact area between the 2 supply wires causing it to ionize. This ionized air conducts electrical current driven by the voltage drop across the contact resistance….. this ‘ionic’ current passing thru ionised air is nothing but the sparking you see while connecting the 2 supply wires directly (or short circuiting them)
    I hope this explanation is sufficient. If you need a more detailed explanation, please let me know.
     
  7. speeed_777

    Thread Starter Active Member

    Oct 5, 2008
    54
    0
    YOUR ANSWER IS EXCELLENT......;)THERE IS NO MORE CONFUSION NOW..
    THANX FOR READING ME...:D
     
  8. b.shahvir

    Active Member

    Jan 6, 2009
    444
    0
    :) Glad to be of help buddy
     
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