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What is 'charge'

  1. Jul 27, 2005 #1


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    I was trying to explain a little bit about electricity to my friend and i came across a problem. What exactly is "charge". I know you can say that a proton has this charge or an electron has this charge and we know what they do... but what exactly IS a charge?
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  3. Jul 27, 2005 #2
    It's the intrinsic property of a particle that interacts with the electromagnetic field.

    How would you answer 'what is mass'?

    Most people would answer 'it's what makes things heavy'. What does heavy mean? a) resists acceleration (inertia); b) moves towards the source of a gravitational field (gravity).

    Similarly, 'charge' is what makes things resist acceleration (radiation force), and move towards or away from the source of an electric field, and move perpendicular to a magnetic field.

    Like Batman said, it's our actions that define what we are.
  4. Jul 27, 2005 #3


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    My friend is having a hard time understanding because he just "cant understand it without seeing it and thinking 'this is a charge'" (after picking up a case of cds and scissors) and i tried to explain it and i also realized I didn't know how to go beyond "its the properties of a particle that....". Sounds like i need to watch more Batman before i go into my next physics courses :D
  5. Jul 27, 2005 #4
    Show him some lightning. That's charge in motion.
  6. Jul 27, 2005 #5


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    Well what you see is light though so it doesnt really count as an instance where you literally "see" charges.
  7. Jul 27, 2005 #6


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    Maybe that is the problem. I recall reading a paper (in AJP?) on semantics in physics which suggests that "mass" and "charge" are properties (in accord with El Hombre Invisible) like "color" is a property. [I'm not completely sure... so don't quote me.] So, it's not "a charge" but "an object with charge", etc.

    While this alone might not help you explain "charge", maybe you need a demo.... like the "sticky-tape" demo (e.g. http://www.amasci.com/emotor/sticky.html .. it seems on that site, there is another page "WHAT IS "ELECTRIC CHARGE?" http://www.amasci.com/elect/charge1.html which I haven't read thoroughly).
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  8. Jul 28, 2005 #7
    Probably your best bet is to first undo his idea of what something more simple like 'mass' is. If you can convince him that you can really only define what mass is by what it does (inertia, gravity) then you'll get him into the right state of mind. After all - you can't 'see' mass either. Try undoing some of his preconceptions in this kind of area, such as that mass is resposible for contact forces (i.e. what stops us walking through walls). When you can get him to understand mass, then apply the same logic to charge, again by explaining how it behaves rather than where it comes from. I think I'd find that heplful at that level.
  9. Jul 28, 2005 #8


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    Well i coulnd't even explain special relativity to him without him doin the old 'no no thats wrong... look at the biological clocks in this situation'.
  10. Jul 30, 2005 #9
    I would also suggest that you go with El Hombre Invisible suggestion. And also you can be a little honest and simply say that nobody really knows what charge is! The truth is once we get down to really fundamental ideas then we can't explain what it is but instead how it behaves. I mean if you think about anything deep enough we will not know what it is because we will end with questions like what really is interia or mass. So it is futile to explain what it is sometimes until some breakthrough leads to an understanding of something else that causes charge and then we won't know what that is but just how it behaves. So tell your friend to snap out of his/her current state of not be able to grasp ideas simply because we don't know what they are.
  11. Jul 31, 2005 #10

    Claude Bile

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    We know a hell of a lot about charge, we know exactly how it behaves and what effect it exerts on other objects around it.

    You can't describe fundamental properties in terms of more fundamental properties (obviously since they wouldn't be fundamental otherwise). Point is, we know what how it behaves and how it influences the world around it, and that is all we really need to know.

    Of course, it could emerge in the future that charge is not fundamental, but rather a by product of a more fundamental property, in which case we could describe charge in terms of something more fundamental.

    But until then, I'm happy to describe charge as a fundamental property of elementary particles.

  12. Aug 16, 2005 #11
    I was having similar confusions about charge,but when i did Helmholtz experiment in lab which aims at finding e/m,all my confusions disappeared after seeing electrons in motion!!
  13. Aug 16, 2005 #12
    what is charge?
    what is mass?
    what is energy?
    that are questions that u cant answer. mass is thought to be answered by the higgs particle but thats a theory yet.
  14. Aug 16, 2005 #13


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    Well, you can start by asking your friend if he believes in the existence of air, even if he can't see it.

    If he doesn't believe in air, a few experiments come to mind, but unfortunately they are unsafe, so I won't post them.

    Assuming you get past the "beliving in air" problem, point out that you can detect charge with a variety of instruments, the gold-leaf electroscope would probably be the best choice as it is fairly simple and detects static charges.
  15. Aug 16, 2005 #14
    There all anthropic labels used to define characteristics :biggrin:
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