Question

Two small spheres spaced 20.0cm apart have equal charge. How many excess electrons must be present on each sphere if the magnitude of the force of repulsion betweenthem is 4.57x10^-21N?

Answer 1

F = kq1q2/r²

q1 = q2

4.57 x 10^-21 = 9 x 10⁹ x q²/(0.2)²

q² = 0.0203 x 10^-30

q = 0.143 x 10^-15 C

now,

ne = 0.143 x 10^-15

n = 0.89

hence, n must be a integer, hence, n can be 1 atleast.