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pivoxa15
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A current will produce a magnetic field but I don't think an electric field will be produced. Why is that? Why is a test charge affected by a static charge but not a moving charge?
Because a current-carrying wire (I assume that's what you are referring to) has no net charge (nor is there a changing magnetic field, assuming a constant current).pivoxa15 said:A current will produce a magnetic field but I don't think an electric field will be produced. Why is that?
Why do you think that?Why is a test charge affected by a static charge but not a moving charge?
Doc Al said:Because a current-carrying wire (I assume that's what you are referring to) has no net charge (nor is there a changing magnetic field, assuming a constant current).
If it were a current of just charge carriers without a wire--a beam of electrons in a vacuum chamber, for instance--then there would certainly be an associated electric field.
Doc A said:Why do you think that?
pivoxa15 said:Is it because the wire acts as an insulator
Realize that by definition an insulator is something that cannot conduct an electric current; the wire, of course, is a conductor not an insulator. But if you look at a section of the wire, what's the net charge on it? Zero! So the net electric field is also zero.pivoxa15 said:Why is this the case? Is it because the wire acts as an insulator so charges inside the wire will not show up on the outside of the material so anything outside will not know of any electric charges anywhere.
Right.pivoxa15 said:Maybe I was wrong. A test charge should be affected by a moving charge just as much as it is affected by a static charge.
In an ordinary metal wire, the only charges that are moving are the negative electrons. The positive charges are fixed in a lattice and are not free to move. (This is not the case in many other kinds of materials that can conduct a current.)borisleprof said:So remember that, there is always the two kinds of charges moving in the wire.
I think you mean the net electric field contributed by that section of wire is zero. Of course, there must be an electric field in the wire if current is flowing.Doc Al said:But if you look at a section of the wire, what's the net charge on it? Zero! So the net electric field is also zero.
Doc Al said:(Regarding the current-carrying wire)
Realize that by definition an insulator is something that cannot conduct an electric current; the wire, of course, is a conductor not an insulator. But if you look at a section of the wire, what's the net charge on it? Zero! So the net electric field is also zero.
Perhaps you are thinking that the current is "extra" charge added to the wire? Not so. It's just a forced movement of the electrons that already exist in the wire. (Any electrons added at one end are being removed at the other end.)
(Regarding the test charge)
Right.
You seem to be forgetting that the wire contains as many protons as electrons. The protons are fixed and don't move. The electrons move but for any given volume, the number leaving is equal to the number entering, so there is no change. The ratio of electrons and protons always remains at 1.00000000000...pivoxa15 said:But we are considering a plain wire so I will stick to that. If we have a circuit with charges flowing, let's consider the whole circuit by enclosing a surface over it. The charges may be moving inside this surface but they will always be inside it hence a net charge exists and electric field lines will extend outside and a test charge will feel it. But this contradicts your explanation. Maybe your explanation works only when the wire is infinitely long?
An electric field (created by the potential difference between cathode and anode) is required in order for electrons to leave the cathode and create a current. The electron flow does not affect the electric field between the anode and cathode. That field depends only on the potential difference that is applied.Why is it that a current of just charge carriers without a wire--a beam of electrons in a vacuum chamber, then there would be an associated electric field? Is it because we are not measuring the electric field with respect to a portion of space such as wire but always to the charges themselves. Hence the Electricfield is moving with the charge carriers?
Andrew Mason said:You seem to be forgetting that the wire contains as many protons as electrons. The protons are fixed and don't move. The electrons move but for any given volume, the number leaving is equal to the number entering, so there is no change. The ratio of electrons and protons always remains at 1.00000000000...
An electric field (created by the potential difference between cathode and anode) is required in order for electrons to leave the cathode and create a current. The electron flow does not affect the electric field between the anode and cathode. That field depends only on the potential difference that is applied.
AM
It doesn't have to be electrically neutral. You can easily create a charged conductor. An airplane frame is often a charged conductor as it flies, so all of the electrical circuits connected to the frame will have a static charge. But that static electric charge that does not change when current flows or stops flowing in those circuits.pivoxa15 said:So you are saying that copper when in a block of solid must be electrically neutral? How can you tell?
And that is why a cathode ray oscilloscope works: the electron beam is deflected by electric charge on plates placed horizontally and vertically around the electron beam.However, charges moving in a vacuum will have an electric field because there are no protons to cancel their charges.
A current, or the flow of electric charge, produces an electric field around it due to the movement of charged particles. This means that any charged particle moving within the current will create its own electric field, and all of these individual fields combine to create the overall electric field produced by the current.
The relationship between a current and an electric field is that a current produces an electric field. The strength of the electric field is directly proportional to the magnitude of the current, meaning that a larger current will produce a stronger electric field.
No, a current cannot exist without producing an electric field. As mentioned earlier, the movement of charged particles within the current creates individual electric fields, and these fields combine to form the overall electric field produced by the current. Therefore, a current and an electric field are inseparable.
An electric field produced by a current can be measured using an instrument called an ammeter. An ammeter measures the strength of the current and can also indirectly measure the strength of the electric field by measuring the force experienced by a charged particle due to the field.
Yes, an electric field can be produced without a current. Electric fields can also be produced by stationary charged particles, such as an electron or a proton, or by changing magnetic fields. However, a current is one of the most common and easily producible sources of electric fields.