Power lines from an electrically charged ball

[Karol]

Homework Statement

A conductive ball of diameter 0.4 [m] is charged equally with a concentration of [itex]\sigma=8 [micro-coulon/m^2][/itex].
What's the total number of electric field power lines, N, that extrude from the ball

Homework Equations

The electric field near a conductor is like in a capacitor:
##E=\frac{\sigma}{\varepsilon_0}##
Definition of power lines:
##\frac{N}{A}=\varepsilon_0 E##

The Attempt at a Solution

##N=A\cdot \varepsilon_0 \cdot E=\frac{A\cdot\varepsilon_0\cdot\sigma}{\varepsilon_0}=A\cdot \sigma##
##N=4\pi\cdot 0.4[m]^2\cdot 8E-6[Coulon]=1.6E-5[lines]##
It should be N=4E-6[lines]

 

[andrevdh]

R = 0.2 m