일반물리학 2 — Gauss' Law: Problem 25

25 Two charged concentric spherical shells have radii 10.0 cm and 15.0 cm. The charge on the inner shell is $7.50 \times 10^{-8}$ C, and that on the outer shell is $6.33 \times 10^{-8}$ C. Find the electric field (a) at $r = 12.0$ cm and (b) at $r = 20.0$ cm.