Respostas

2013-12-28T13:11:51-02:00
Lei de Coulomb:

F = K.Q1.Q2 / d²
F = Força
K = constante ~> 9.10⁹
Q1 Q 2 são as cargas
d = distancia

a) Se Q1 = 4/3Q2

5cm = 0,05 m

F = K.Q1.Q2 / d²
12.10⁻⁵ = 9.10⁹ . 4/3Q2 . Q2 / (0,05)²
12 . 10⁻⁵ . 25 . 10⁻⁴ = 9 . 10⁹ . 4/3 Q2²
300 . 10⁻⁹ = 12.10⁹ Q2²

Q2² = 300 . 10⁻⁹ / 12.10⁹
Q2² = 25 .10⁻¹⁸

Q2 = 5 .10 ⁻⁹ C

Voltando :  Q1 = 4/3Q2
Q1 = 4/3 . 5 .10 ⁻⁹
Q1 = 20/3 .10⁻⁹ C

{ Q1 = 20/3.10⁻⁹ C  e Q2 = 5 .10 ⁻⁹ C }


B)  Se Q1 =  Q2 /3

F = K.Q1.Q2 / d²

12.10⁻⁵ = 9.10⁹ . Q2 /3 . Q2  / (0,05)²

12 .10⁻⁵ . 25 .10⁻⁴ = 3 . 10 ⁹ . Q2²
300 . 10⁻⁹ = 3.10⁹ . Q2²
100 .10⁻¹⁸ = Q2²

Q2 = 10.10⁻⁹ ~> 1.10⁻⁸

Voltando : Q1 =  Q2 /3

Q1 = 1.10⁻⁸ / 3  C

{ Q1 = 1/3 . 10⁻⁸  C e Q2 =
1.10⁻⁸ C}