# Homework Help: Current Density

1. May 15, 2004

### oggrol

Let E=Eo (err...free space, not sure how to represent the symbols)
V=90z^(4/3) in the region z=0(Potential)
a) Find expressions for E,D and pv (volume charge density) as functions of z

My work:
E=-div V=0+0)120z^(1/3)az=120z^(1/3)az V/m
D=Eo E=1.062z^(1/3)az nC/m^2
pv=div D=.354/z^(2/3) nC/m^3

b)If the velocity of the charge density is given as vx=5x10^6 *z^(2/3) m/s, find Jz (current density) at z=0 and z=.1m

My work:
Now this is where I am confused because J=pv*v (volume charge density*velocity vector). And the book only gives the x component of the velocity vector and asks for the z component of the current density. If you ask me, that means the z component of the current density is 0, but I have no way of checking my answer.

Is this correct?

Last edited: May 16, 2004
2. May 16, 2004

### oggrol

Still not sure about part b of this one, and running into more problems with the stuff

3. May 18, 2004

### oggrol

Teacher posted solutions today....