- #1
Observer Two
- 25
- 0
I want to derive this equation:
[itex]V(r) = \frac{1}{\epsilon_0} [\frac{1}{r} \int_0^r \! r'^2 \rho(r') \, d r' + \int_r^{\infty} \! r' \rho(r') \, d r' ][/itex]
of a spherical charge distribution.
I can do it with the general integral definition of the electrostatic potential (which is basically the utilization of the Greens function). But isn't it also possible to derive it directly from the Poisson equation:
[itex]\nabla^2 V(r) = -\frac{\rho(r)}{\epsilon_0}[/itex]
Using spherical coordinates:
[itex]\frac{1}{r^2} \frac{\partial}{\partial r}(r^2 \frac{\partial V(r)}{\partial r}) = -\frac{\rho(r)}{\epsilon_0}[/itex]
[itex](r^2 \frac{\partial V(r)}{\partial r}) = -\int \! \frac{\rho(r)}{\epsilon_0} r^2 \, d r [/itex]
Here is the part where I'm stuck. I could maybe "split" the right hand side in the following way:
[itex](r^2 \frac{\partial V(r)}{\partial r}) = \frac{1}{\epsilon_0} [\int_r^{\infty} \! \rho(r') r'^2 \, d r' + \int_0^r \! \rho(r') r'^2 \, d r'][/itex]
But then I'm lost how to continue since there is another derivative on the left hand side.
[itex]V(r) = \frac{1}{\epsilon_0} [\frac{1}{r} \int_0^r \! r'^2 \rho(r') \, d r' + \int_r^{\infty} \! r' \rho(r') \, d r' ][/itex]
of a spherical charge distribution.
I can do it with the general integral definition of the electrostatic potential (which is basically the utilization of the Greens function). But isn't it also possible to derive it directly from the Poisson equation:
[itex]\nabla^2 V(r) = -\frac{\rho(r)}{\epsilon_0}[/itex]
Using spherical coordinates:
[itex]\frac{1}{r^2} \frac{\partial}{\partial r}(r^2 \frac{\partial V(r)}{\partial r}) = -\frac{\rho(r)}{\epsilon_0}[/itex]
[itex](r^2 \frac{\partial V(r)}{\partial r}) = -\int \! \frac{\rho(r)}{\epsilon_0} r^2 \, d r [/itex]
Here is the part where I'm stuck. I could maybe "split" the right hand side in the following way:
[itex](r^2 \frac{\partial V(r)}{\partial r}) = \frac{1}{\epsilon_0} [\int_r^{\infty} \! \rho(r') r'^2 \, d r' + \int_0^r \! \rho(r') r'^2 \, d r'][/itex]
But then I'm lost how to continue since there is another derivative on the left hand side.