7. The earth has a net electric charge that causes a field at points near the su

Question

7. The earth has a net electric charge that causes a field at points near the surface equal to 150 NIC and directed towards the center of the earth. ~?

(a) What is the netelectric.flux at the surface of the earth?

(b) What is the magnitude of the net electric charge of the earth? Is it positive or negative?

8. EXTRA CREDIT Consider an infinitely long cylinder of radius R that is uniformly charged throughout its volume. The charge density per volume is p (C/m What is the electric field outside the cylinder at a distance r > R from the axis?

Explanation / Answer

7. elelctric flux = EA cos theta

Area here A = 4pir^2 = 4*3.14* 6400000^2

A = 2.57 *10^14 m^2

so flux =     150 * 2.57 e14

flux = 3.855*10^15 Nm^2/C
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Apply E = Kq/r^2

charge q = Er^2/K

q = 150 * 6400000^2/9e9

q = 6.85 *(10^5 ) C
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electric field E due to cylidrical symmetry is definedby

E = (rho) r/(2e0)

where eo is permittivity constant = 8.85e-12
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