Question

5. Two identical conducting spheres hang from a light-weight string carry 10 nC of charges each maintain equilibrium state at a distance of 5 mm from each other while making 0-10o from the vertical line. Find the weight of the spheres.

Answer 1

drawing an fbd and doing force balance we get

vertical force balance

T*cos($\theta$) = W {W is the weight}

horizontal force balance

F= T*sin($\theta$)

and also

F= kq²/r² = 9*10⁹*(10*10^-9)²/ (0.005)²

F = 0.036 N

dividing both equations

tan($\theta$) = F/W

W = F/(tan($\theta$))

putting the values

W=0.2041 N