## Charge and current density

Can we make a mathematical (equation) relationship between Current Density and Charge Q.
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 hmm... it seems to me that without any additional information it is only possible to connect dQ/dt with j.
 I am trying to find Q using a relationship in which there is no area A. Knows are electric potential U Total flux density D Total Field Intensity E Current Density Inductance.

## Charge and current density

There is a relationship between charge density and current density; the charge continuity equation.
 Oscar6330, could you please be more specific? What is the physical system you are trying to describe? For instance, A is area of what? U is electric potential between what points? and so forth...
 In a relativistic theory charge density and spatial current density form a four vector current density j_\mu. In the non relativistic limit they are related by the continuity equation.
 I am trying to find out the capacitance of a system. Now C=Q/V. I am using a Simulation software. The only output parameters available are electric potential U Total flux density D Total Field Intensity E Current Density J Inductance. I am really stuck with it and need help as I am not a Physics guy. Pl tell me some equation
 I don't quite understand... What is total field intensity? at what point? and what is flux density? If field intensity E is known on the surface S of the conductor you can integrate it over the surface to get total charge Q (Gauss's law) $$Q = \varepsilon_0 \int_{S} E_n dA$$. Capacitance C is then C = Q/U. I have a feeling that flux density is just $$\textbf{D} = \varepsilon_0 \textbf{E}$$ so $$Q = \int_{S} D_n dA$$ But I'm not sure... May be capacitance of your system has already been calculated by someone? =)
 LOL....well since this is not an assignment, so no one has solved it. So the problem still remains unsolved

 Quote by naturale In a relativistic theory charge density and spatial current density form a four vector current density j_\mu. In the non relativistic limit they are related by the continuity equation.
It's a relativistic equation as well. The charge continuity equation is Lorentz invariant, and more, is covariant without connections on a curved spacetime.
 Ok. what i mean is that in the non relativistic limit the charge density is give by j_0 \propto |\phi^2| and it can be associate to a quantum probability but in the relativistic limit the charge density it is not positively defined and thus it is not consistent with a probability interpretation. J_0 \propto \phi* (d_t \phi) - (d_t \phi*) \phi.
 I don't know what a relativistic limit is. Usually you want to keep things at v
 To be honest, I cannot understand where its going. Can you guys please redirect to my topic
 you are right. the relativistic interpretation of the charge density as a probability can be the object of another topic.

 Quote by Oscar6330 To be honest, I cannot understand where its going. Can you guys please redirect to my topic
Sure, Oscar. Without a little more to go on, we don't know what to go on. You need to explain your system.

 Quote by naturale you are right. the relativistic interpretation of the charge density as a probability can be the object of another topic.
That sounds interesting. Why don't you start a thread?
 Well it is very simple. I want to compute capacitance C. Now from my simulation software i can only get the following outputs, which are electric potential V Total flux density B Total Field Intensity H Current Density J Inductance. So I just want an equation, which has these variables only to calculate Capacitance (and some constants)