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Thread: Another stupid question..

  1. #1 Another stupid question.. 
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    Can electric sparks occur in the absence of another object with opposite polarity? i.e. can a negatively charged object start an electric spark even though there are no nearby objects that are positively charged. Just wondering.


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    Brassica oleracea Strange's Avatar
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    I guess you could have sparks between two objects with different levels of negative charge; voltage difference is relative.


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    ei incumbit probatio qui dicit, non qui negat
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    Quote Originally Posted by molecool View Post
    Can electric sparks occur in the absence of another object with opposite polarity? i.e. can a negatively charged object start an electric spark even though there are no nearby objects that are positively charged. Just wondering.
    Actually, I think I recall reading that often a highly charged object can induce a mirror image charge, i.e. of opposite polarity, in another object that is brought close to it. For example, a charged thundercloud can induce a mirror image charge on the surface of the Earth. This makes intuitive sense, in that the electric field it produces will tend to polarise objects in that field.
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    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by molecool View Post
    Can electric sparks occur in the absence of another object with opposite polarity? i.e. can a negatively charged object start an electric spark even though there are no nearby objects that are positively charged. Just wondering.
    Actually, I think I recall reading that often a highly charged object can induce a mirror image charge, i.e. of opposite polarity, in another object that is brought close to it. For example, a charged thundercloud can induce a mirror image charge on the surface of the Earth. This makes intuitive sense, in that the electric field it produces will tend to polarise objects in that field.
    You mean electrostatic induction?
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  6. #5  
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    Quote Originally Posted by molecool View Post
    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by molecool View Post
    Can electric sparks occur in the absence of another object with opposite polarity? i.e. can a negatively charged object start an electric spark even though there are no nearby objects that are positively charged. Just wondering.
    Actually, I think I recall reading that often a highly charged object can induce a mirror image charge, i.e. of opposite polarity, in another object that is brought close to it. For example, a charged thundercloud can induce a mirror image charge on the surface of the Earth. This makes intuitive sense, in that the electric field it produces will tend to polarise objects in that field.
    You mean electrostatic induction?
    Yes.
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    Quote Originally Posted by molecool View Post
    Yep that's good example of ionisation taking place with no other conductor close by at all.
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    Quote Originally Posted by molecool View Post
    Can electric sparks occur in the absence of another object with opposite polarity? i.e. can a negatively charged object start an electric spark even though there are no nearby objects that are positively charged. Just wondering.
    An object cannot spark on its own.

    If two objects are not equally charged, you need 10,000 volts per centimetre of air to create a spark.
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  10. #9  
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    Quote Originally Posted by Unununium View Post
    Quote Originally Posted by molecool View Post
    Can electric sparks occur in the absence of another object with opposite polarity? i.e. can a negatively charged object start an electric spark even though there are no nearby objects that are positively charged. Just wondering.
    An object cannot spark on its own.

    If two objects are not equally charged, you need 10,000 volts per centimetre of air to create a spark.
    Not equally charged but of opposite polarity?
    And what about the corona discharge I posted earlier?
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    Whadt
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