الفيزياء العامة الجزء الثاني#موقع الفيزياء.كوم

Lectures in General Physics
A volume charge distribution
In figure 4.16 shows an insulating sphere of radius a has a uniform charge
density ρ and a total charge Q.
1) Find the electric field at point outside the sphere (r>a)
2) Find the electric field at point inside the sphere (r<a)
For r>a
Aa
Rr
E
Figure 4.16
We select a spherical gaussian surface of radius r, concentric with the
charge sphere where r>a. The electric field E is perpendicular to the
gaussian surface as shown in figure 4.16. Applying Gauss law we get
∫ E r
=
r q . dA in
ε ο
2 Q
∫ A = E(4πr
)
εο
E =
Q
∴ E = (for r>a) (4.10)
2
4πε ο
r
Note that the result is identical to appoint charge.
Dr. Hazem Falah Sakeek