cepheid said:
I'm not sure what you mean by 'cancelling with.' I mean, your quoted statement said there was a NET charge on the sphere. Net means surplus. So there must be some unbalanced charge present. Otherwise the total charge would just be zero, not Q.
But then what is the point of charging it if the conductor is already going to have a net charge? Like I have a conducting sphere, inside has more electrons than protons and therefore the net charge is negative, if we already know that why are we charging it?
Of course free electrons can move in a conductor. That's why we call them "free" electrons. If there is no electric field present, all this means is that there are no forces acting on those electrons. It doesn't mean that they don't move. In any case, I don't see what this has to do with anything or how you arrived at it.
site question said:
They also distribute themselves so the electric field inside the conductor is zero. If the field wasn't zero, any electrons that are free to move would. There are plenty of free electrons inside the conductor (they're the ones that are canceling out the positive charge from all the protons) and they don't move, so the field must be zero.
You say that free electrons move, but this site say they don't. I don't even understand what they mean by distributing themselves so that the E-field is 0. This concept has been bothering me for weeks now. In my textbook, it says this occurs when an external field is applied to a conducting slab to create a field of 0
This is what my textbook did
[PLAIN]http://img651.imageshack.us/img651/9509/92678195.jpg
Now I am assuming that a zero field inside meant that this will happen, where there exist a field inside, there is also an external field outside therefore the net field is 0 and therefore there is no field inside.
[PLAIN]http://img403.imageshack.us/img403/6589/52447869.jpg
Now here is the thing, why can't the following scenario happen?
Scenario A
Since there is a E-field generating, that means a positive charged thing must be producing this E-field, so why can't the E-field terminate when it touches the negative charge? Or does it go further? But that is assuming the positive charge has a greater charge such that it can go pass through the slab
[PLAIN]http://img843.imageshack.us/img843/4670/76394506.jpg
Now my book also said this
book said:
As the electrons move, the surface charge densities on the left and right surfaces increase until the magnitude of the internal field equals that of the external field, resulting a net field of zero inside the conductor
What does that mean? What do they mean "increase", what if there is not enough electrons to make that happen?
Scenario B
In all my HW problems where they want you to say that the E-field is 0 for a conductor, they say it like this.
A spherical solid conductor has a net charge of -25uC (an excess of electrons) and has a radius of 10cm. What is the E-field at a) r = 5cm, b)r = 15cm
Okay so this is a conductor, a textbook method of answering would say this is zero because this is inside a conductor, almost just memorizing. But according to the book, this happens only if there is an external E-field to make that happen, but in problems like these it doesn't even say it. Perhaps when a conductor is charged, we immediately assume that it must be in
electrostatic equilibrium? But if the charges are "spread out" as we want to believe, that still doesn't mean the E-field is 0 since there is no external E-field to make the inside a zero net field
So perhaps something like this would happen. You got all the negative charges on the surface and some positive charges inside. Clearly there is field and notice the charges have been distributed uniformly (so it was once charged), but once the thing we used to charge is removed (the external field), the field inside wouldn't be zero anymore
[PLAIN]http://img834.imageshack.us/img834/9910/58991724.jpg
