試題詳解

50. Charges are distributed non-uniformly in between the space of two infinitely long concentric cylinders of radius R and 2R,respectively, as shown in the figure on the right. There is no charge in the region r <  R and r > 2R. In the region R<r<2R， the charge density only depends on the radial distance p(r)= C/r, and C > 0. In addition, a metal shell is attached to the surface of the outer cylinder, and it is grounded with the electric potential set to 0. Which of the following statements is true? 
(A) The electric field in the region R < r < 2R decays with r.
(B) The electric potential in the region R <r < 2R decays linearly with r.
(C) There is a positive surface charge residing on the inner surface of the outer cylinder.
(D) The electric potential in the cavity region is 0.
(E) None of the above.