- #1
Kernul
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Homework Statement
A point charge ##q = 30 mC## is located in the center of a conductor spherical shell with an internal radius of ##a = 10 cm## and an external radius of ##b = 20 cm## and total charge null.
Find the surface density charge of both the internal surface and external surface of the conductor and draw a graph of the module of the electric field as a function of the distance from the center of the sphere.
Homework Equations
Gauss Theorem
##\Phi_S(\vec E_0) = \int_S \vec E_0 \cdot d\vec S = \frac{Q_{TOT}^{int}}{\epsilon_0}##
The Attempt at a Solution
I started this way and applied the Gauss Theorem on the internal surface and external surface, so
##E 4 \pi r^2 = \frac{Q_{TOT}^{int}}{\epsilon_0} = \frac{\sigma 4 \pi a^2}{\epsilon_0}##
##E 4 \pi r^2 = \frac{\sigma 4 \pi b^2}{\epsilon_0}##
which become
##\sigma_{int} = \frac{E r^2 \epsilon_0}{a^2}##
##\sigma_{ext} = \frac{E r^2 \epsilon_0}{b^2}##
and I thought I did it right, but when the exercise asks me to draw a graph of the electric field as a function of the distance form the center I noticed that the exercise says "total charge null" in the conductor. This means that ##Q_{TOT}^{int} = 0##, right? So the two surface density charges I found are wrong? And how should I draw the graph?