Question

Two identical metallic spheres are suspended as bobs of a simple pendulum as shown in the figure. The spheres come to equilibrium when given a charge of +7.5 x 10^-9 C, with each string making an angle 5⁰ with the vertical. The string is 0.5 m long. Find the electric force between the spheres.

Answer 1

Answer

Given

q=q'=$+7.5 \times 10^{-9 }C,$

l=0.5m

$\theta=5°$

According to given data electric force is given by

$F_e=\frac{kqq'}{(2lsin\theta)^2 }\\=\frac{9\times10^9\times7.5 \times 10^{-9 }\times 7.5 \times 10^{-9 } }{(2\times0.5sin5°)^2 }\\=\frac{506.25\times10^{-9}}{0.759}\\=6.67\times10^{-9}N$