Question

 Two small metal spheres are 30.0 cm apart. The spheres have equal amount of negative charges and repel from each other with a force of 40.0 N. What is the charge on each sphere?

Answer 1

We have,

$d= 30cm = 0.3m$

$F = 40N$

$q_1 = q_2 = -q$

We know,

$F = \dfrac{1}{4\pi \epsilon_0} \dfrac{q_1q_2}{d^2}$

After putting values we get,

$40 = \dfrac{1}{4\pi\epsilon_0} \dfrac{q^2}{0.3\times 0.3}$

$q^2 = 40\times 4\pi\epsilon_0\times 0.3 \times 0.3$

We get,

$q = 0.632\times 10^{-3} C$