A hollow conducting spherical shell has radii of 0.80 m and 1.20 m,as shown in the figure.The sphere carries a net excess charge of -500 nC.A point charge of +300 nC is present at the center.
(k = 1/4πε₀ = 8.99 × 10⁹ N • m²/C) The radial component of the electric field at a point that is 1.50 m from the center is closest to

Question

Quizplus · Accepted Answer

Since the point charge is at the center, it does not contribute to the electric field at a point outside of the sphere. Therefore, the electric field at a point 1.50 m from the center is due entirely to the net charge on the spherical shell. 
Using Gauss's law, we know that the electric field at any point outside of a closed surface enclosing a net charge is proportional to the net charge and inversely proportional to the distance from the center of the charge. Therefore, the electric field at a point 1.50 m from the center of the spherical shell is given by:
E = (kQ/R^2) = (8.99 × 10^9 N • m^2/C^2)(-500×10^-9 C)/(1.50 m)^2
E = -800 N/C
Therefore, the radial component of the electric field at a point that is 1.50 m from the center is closest to -800 N/C, which is choice C.

A Hollow Conducting Spherical Shell Has Radii of 0