所=小ar店6r 1-1 8π60 RR 1 92 32π2cr4 dx=4πr2dr ◆dW。=wdt∫ = dτ wW ee ∫ = 21 d 8π 2 0 2 R R r r q ε 4d π drr 2 τ = 2 e 0 2 1 = ε Ew dd τ = wW ee 4 0 2 2 32π r q ε = R2 R1 q −q r dr ⎟⎟⎠⎞ ⎜⎜⎝⎛ = − 210 2 11 8π RR qε