Application of Gauss's Law to Charged Insulators

[EngineerHead]

Homework Statement

A cylindrical shell of radius 7.00 cm and length 240 cm has its charge uniformly distributed on its curved surface. The magnitude of the electric field at a point 19.0 cm ra- dially outward from its axis (measured from the midpoint of the shell) is 36.0 kN/C. Use approximate relationships to find (a) the net charge on the shell and (b) the electric field at a point 4.00 cm from the axis, measured radially outward from the midpoint of the shell.

Homework Equations

The Attempt at a Solution

Could someone please explain to me why this does not work:

Flux = Q/e = E*2pi*r*l

Where I am thinking of Q in terms of an average AREA charge density * the area, and not a line density * a length.
-- Is it because it lacks enough independent equations?

 

[Doc Al]

Why do you think that doesn't work?

 

[EngineerHead]

Because I am currently getting a different answer than that given by the book - which is:

+913 nC

 

[EngineerHead]

Okay it works... I've been using an incorrect value for e when solving from k - apologies.