일반물리학 2 — Gauss' Law: Problem 35

35 The electric field in a certain region of Earth’s atmosphere is directed vertically down. At an altitude of 300 m the field has magnitude 75.0 N/C; at an altitude of 200 m, the magnitude is 210 N/C. Find the net amount of charge contained in a cube 100 m on edge, with horizontal faces at altitudes of 200 and 300 m.