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Homework Statement
Using Dirac delta function in the appropriate coordinates, express the following charge distributions as three-dimensional charge densities p(x).
(a) In spherical coordinates, a charge Q uniformly distributed over a spherical shell of radius a.
(b) In cylindrical coordinates, a charge [itex]\lambda[/itex] per unit length uniformly distributed over a cylindrical surface of radius b.
(c) In cylindrical coordinates, a charge Q spread uniformly over a flat circular disc of negligible thickness and radius R.
(d) The same as in (c), but using spherical coordinates.
Note that
[tex] \delta(x-x')= \frac{1}{|J(x_i, \zeta_i)|} \delta( \zeta_1 - \zeta_1')\delta( \zeta_2 - \zeta_2')\delta( \zeta_3 - \zeta_3')[/tex]
where [itex]J(x_i, \zeta_i)[/itex] is the Jacobian relating cartesian coordinates [itex](x_1,x_2,x_3)[/itex] to new coordinates [itex](\zeta_1,\zeta_2,\zeta_3)[/itex].
Homework Equations
[tex]\int_{- \infty}^{+ \infty} f(x) \delta(x-a) dx = f(a) [/tex]
The Attempt at a Solution
For some reason I can't wrap my head around how to methodically do this problem. Let's start by discussing part (a). Here is what I have:
(a)
The definition of charge density is: [tex] \rho = \frac{TotCharge}{TotArea}[/tex]
In this case then, we get: [tex] \rho = \frac{Q}{4 \pi a^2}[/tex].
However, this charge is localized to the surface of the sphere where r=a, so:
[tex] \rho(r)=\frac{Q}{4 \pi a^2} \delta(r-a)[/tex]
is this a correct answer? it doesn't seem to be three dimensional, but then again [itex]\theta[/itex] and [itex]\phi[/itex] seem like irrelevant values since the charge is localized to the surface where r=a. Doing a check integration of the charge density in 3d space produces the total charge Q, so I have reason to believe it is correct..
As far as the rest of them go, I could use some help as to how to get started/use that jacobian equation.