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What is charge and what are the reality of fields?

  1. Mar 20, 2008 #1
    please what is the charge and is there anything else except +ve -ve and neutral and what is the electric field?
    I don't want to know on what it depends but i want to know what is it matter or what and then comes my question why a force of magnetic field moves a wire from the high magnetic flux to the low magnetic one density can one reverse it ????
    Don't tell me that charge is a property i know i want to know why as an example an electron takes it's -ve charge ? many questions also why is the nucleus sphered and why electrons revolve in circular orbits not any other shape and can we change the charge of electron????or reverse it's path or stop it ?????????
    Please i am still newbie but i am enthusiast to think.........
  2. jcsd
  3. Mar 20, 2008 #2


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    Gold Member

    Hi Ahmed,
    There is only +ve and -ve electric charge. Electrodynamics does not say what an electric field actually is, and I doubt if anyone knows for sure.

    Please rethink that question - it's garbled.

    Again this is not answered by our current theories. We know from observation that electrons and positrons are charged. It is a property !

    Keep studying and you will find out more. Electrons don't orbit nuclei, as you will see when you study quantum mechanics.

    It's natural to ask what something really 'is', or what it is made of, but these questions are not always answerable right now.
  4. Mar 21, 2008 #3
    why is heat transfered from high one to the low same in pressure,can one reverse the operation to move things from high pressure to low pressure ????
    Please,tell me are my questions silly people tell me that but i just think that there are always things to know what is your opinion??
  5. Mar 21, 2008 #4
    When either a rubber rod or a glass rod is rubbed with a particular material it will become “electrified” in that it will attract small bits of paper or cloth. The process of rubbing the rod is called charging the rod and the physical change on the rod is that the amount of something on the rod either increases or decreases. This “something” is now referred to as charge. In the days of Benjamin Franklin it was thought that charge was a type of invisible fluid present in all matter. Franklin showed that charge comes in both positive and negative quantities. In fact it was Franklin who coined the terms negative charge and positive charge and hence the term charge was coined. The terms negative and positive refer to whether the charges attract or repel each other. Like charges attract while unlike charges repel. In the years following Franklin it was shown that what was either leaving or gaining charge was the change in the number of charged particles we call electrons. (From the Greek word for elektron which means amber).
    Its an intrinsic property of certain particles/bodies. It is not matter itself just as mass is not matter but merely a property of matter.
    A magnetic field exerts a force on a current carrying wire regardless of the magnetic flux density. In fact if you placed a current carrying wire in a uniform magnetic field such that the direction of the current is perpendicular to the direction of the magnetic field then the magnetic field exerts a force on the wire. As to why; It is an experimental fact that a charged particle moving through a magnetic field will have a force exerted on it by the magnetic field when there is a component of the velocity which is perpendicular to the field direction. Since this is taken as a basic law of physics and not something which can be derived from something more basic, i.e. it is a postulate/axiom/law.
    Sorry. No can do since that is what it is. I'[m not one for lying and since this is the truth then this is what I'm posting. Feel free to ignore this post if this is not what you want to read.
    What is "ve" charge?? What do you mean by "takes it's -ve charge"? The charge of a particle is usually denoted using the letter "q." The charge on an electron is usually denoted by "e."
    The nucleus for large number of nucleons is spherical because the shape of the sphere will given the lowest energy state of the nucleus. However when a nucleus is bombarded by other particles, such as neutrons, it will undergo changes in shape and it some cases will break apart into two or more nuclei.
    Electrons move in circular orbits only in special cases. One such case is a charged particle moving through a uniform magnetic field (in this case the electric field is chosen to be zero) and whose initial velocity is in the a plane whose normal vector is parallel to the magnetic field. Since the magnetic field cannot do work on a charged particle (since the force is always perpendicular to the velocity and tus F*dr = 0 an therefore the kinetic energy remains constant. The potential energy is constant since there is no electric field and thus the total energy is constant. The proper mass of the electron doesn't change). Since the force is perpendicular to the velocity it follows that the angular momentum is constant. Since the force on an electron moving in a uniform magnetic field is not a function of position it can be shown that the radial velocity is zero and the angular velocity is constant. This is the description of a particle moving in a circle. If the particle has a velocity which is parallel to the magnetic field then it won't move in a cirlel but in a helical trajectory.
    Nothing like this has evern been observed under an enormous variety of situations. That's about all that can be said.
    No, not in a puer magnetic field (i.e. electric field is zero). If it did then the energy would change and thus the law of conservation of energy would would be broken.

    Best wishes

    Last edited: Mar 22, 2008
  6. Mar 21, 2008 #5
    thanks very much pmb_phy please tell me a place where i can find a tutorial about the case of revolving of electrons in circular path (is the circular path you mean includes the electron cloud and what is a helical trajectory and why is the electron moving in it's one direction(clockwise or anticlockwise) and why it carries negative charge not positive is that something related to the nature of the nucleus(i mean why can't the protons carry negative and electrons carry positive or why can't we make them neutral i mean not assigned with a charge ) also can we reverse the force acting on the wire so at the same conditions of positioning the wire and the magnet and the current we can make the wire move from the low magnetic flux to the high one????
  7. Mar 21, 2008 #6
    This is a tricky point. Since this is a forum on classical physics, and since you were asking about classical trajectories, I negleted to mention quantum mechanics. To discuss electrons in an atom requires a discussion in quantum mechanics. The "clouds" you speak of refer to a quantum description of motion. When you speak of an electron traveling in a circle you're speaking of a classical trajectory. There are no classical trajectories in quantum mechanics. Regarding a tutorial please check your PM (private messages).
    Sorry but I'm exausted. I'll get to the rest tommorow.

  8. Mar 22, 2008 #7
    Re: what is charge and what are the reality of fields

    I hope you understand this is a controversial topic. A charge is an offensive foul, as you probably already know. I understand your frustration, as this concept even baffles the best of referees. The reality of fields is that they are not always accurate. Sometimes a garbage basketball team (e.g. UGA) makes it to the field of 64.
  9. Mar 22, 2008 #8
    I'm curious as to where you got the idea that this was a controversial subject?? I have met many professional physicists (friends and colleauges) and not one of them thought that there was a controversy regarding this topic. I myself can see nothing wrong with it. If you do then please state the problem and provide justification for it. A reference to a source in the physics literature whose author holds this to be controversial is highly desired.

  10. Mar 22, 2008 #9
    By following basketball.
  11. Mar 22, 2008 #10
    Nobody knows.

    Charge: I would call the charge a particular property of the electric and magnetic fields. By classical definition, it is exactly that.

    Electric field: These two rather famous guys, Kaluza and Klien thought that the electric and magnetic fields could be explained by the shape of space and time, like in relativity theory where space-time can be curved in shape.

    They proposed that there was a fifth dimension so small we weren't aware of it. Curvature in this fifth dimension, they said, could be what the electric and magnetic fields were made of.

    The basic unit of charge (actually the ratio between charge and mass) of an electron may even be determied by how large this dimension might be.
  12. Mar 22, 2008 #11
    Sorry but that is a comment without any meaning to this topic.
  13. Mar 22, 2008 #12
    You either lack a sense of humor, or you need to learn how to read an entire post.
  14. Mar 24, 2008 #13
    Charge is a property of a particle in the way that taste is a property of a soup.
  15. Mar 24, 2008 #14
    It's hard to read what someone has written when they don't put a period at the end of each sentence.
  16. Mar 24, 2008 #15
    Here is my guess, or over simplified explanation:

    A simple definition could be .. The potential for electrons to flow (negative charge) to an area that accepts free electrons (usually positive a charged area).

    The electrical force (that pushes charge) could be considered the total difference in 'force' between all the negitive ions (pushing force on electrons) and positive ions (pulling force on electrons) that attract through a dielectric (voltage). The actual force that moves electrons comes from protons, positrons maybe, and other electrons. Once a conductive path is available between the two charged areas ("vacuum" and "pressurized"), the charged areas try to equalize creating current.
  17. Mar 25, 2008 #16
    charge, like many other "properties" or "tendencies" are difficult to define by using anything other than operationalism and/or effects.


    alice: what is x?
    bob: x is a thing that does a_1 through a_n.
    alice: i didnt ask what it does, i asked what it is.
    bob: oh. x is a type of X that has the special properties y_1 though y_n.
    alice: but why does x have those properties?
    bob: go fish.
  18. Mar 26, 2008 #17
    x is a man made property or you define whatever you did with whatever property but a charge is a constant
    property for any particle in the universe and it is not like the taste of something as the taste of something has it's reasons for being as it is as containing some chemical compounds that reacts with the enzymes in your body to feel that it is sour or delicious by your nervous system so you can define what is taste with the molecular actions and atomic level and it is known now what taste really is........
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