dq =ρ(x)*dx = -eax*dx
q = ∫？(?eax)？dxx
0.5厘米
=-ea/2 *(x2–xm2/4)
= ea/8ε0 * (xm2
— 4x2)
由高斯定律:E = q/ε0 = ea/8ε0 * (xm2