Difference between charge and charge density

  • Thread starter vysero
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vysero
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So I am studying Gauss's law and I am a bit confused about something. If I am asked to compute the volume or surface charge density of a solid perfectly conducing sphere with a charge Q and radius r, what is being asked of me? Am I just being asked to compute the volume of a sphere and multiply it by Q? I am not sure. Here is what I would do:

E = Q/(4(pi)(epsilon)(r^2) therefore Q = E/4(pi)(epsilon)(r^2)

Is this correct or is there a difference between charge Q and charge density?
 

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  • #2
As far as I understand what you are asking they are asking you to calculate charge density on a sphere in terms of Q and r. your awnser ought not to have anything to do with the electric field.
Much like mass density, charge density is the amount of charge/space The surface charge density is defined as amount of charge per unit area of the surface.
The question is how much charge is in a little shell on the surface between radius r and r+dr per unit area.
in other words: ##\frac{q_{surface}}{A_{sphere}}##. Think for a second: what would happen to a bunch of charges inside of a conducting sphere considering that like charges repel. How much of that charge would be on the surface?
 

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