# Homework Help: Determining Electric Flux for cylindrical surfaces

1. Sep 10, 2008

### euphtone06

1. The problem statement, all variables and given/known data
Cylin. surfaces $$\rho$$ = 1 , 2 , 3, cm have uniform surface charge density of 20, -8, 5 nC/m^2.

What is the total electric flux that passes through the closed surface $$rho$$ = 4 cm and z(from 0 to 1 m)?

And what is $$\vec{D}$$ at the point $$\rho$$= 4 cm , $$\phi$$= 0 , z = .5 cm

2. Relevant equations
$$\Phi$$= E2piRL=$$\lambda$$L/8.85x10-12
E = $$\rho$$/(2pi8.85x10^-12 $$\rho$$)

3. The attempt at a solution

So the closed surface from which to determine the flux is at $$\rho$$ = .04 m

I frankly am unsure how to use the equations to get the total flux.

$$\Phi$$1 = 20(.01)/8.85x10^-12
$$\Phi$$2= -8(.02)/8.85x10^-12
$$\Phi$$3= 5(.03)/8.85x10^-12

Is it as simple as adding them all up? Or does the center most cylindrical surface at 1 cm have an affect on 2 cm surface which then in turn affects the 3 cm? I have a feeling this is completely wrong so I attempted it a different way

$$\int$$.04*20
$$\int$$.04*-8
$$\int$$.04*5
total flux = sum of the integrals?

I obviously am struggling with this concept any help would be appreciated Thanks!