Resolução - Halliday - Volume 3 - Eletricidade E Magnetismo - P23 037

Transcript

37. When the drop is in equilibrium, the force of gravity is balanced by the force of the electric field: mg = qE, where m is the mass of the drop, q is the charge on the drop, and E is the magnitude of the electric field. The mass of the drop is given by m = (4π/3)r3 ρ, where r is its radius and ρ is its mass density. Thus, q = = 4πr3 ρg mg = E 3E 4π(1.64 × 10−6 m)3 (851 kg/m3 )(9.8 m/s2 ) = 8.0 × 10−19 C 3(1.92 × 105 N/C) and q/e = (8.0 × 10−19 C)/(1.60 × 10−19 C) = 5.