We will be changing one variable at a time to see how it affects the value of the forces. Set the variables listed in the table and document the force and determine if the charges are attracted to each other or repelled.

Answer:
Explanation:
The coulombs law is expressed as
F = kq1q2/r^2
where
F is the force
k is the coulomb constant and its value is 9 x 10^9 N/m^2C^2
q1 and q2 are the magnitude of the charges
r is the distance between them
From the information given,
r = 4 cm = 4/100 = 0.04m
For trial 1,
q1 = - 2μC
q2 = 8μC
Recall,
1 μC = 1 x 10^- 9 C
q1 = - 2 x 1 x 10^- 9 C
q2 = 8 x 1 x 10^- 9 C
F = (9 x 10^9 x 2 x 1 x 10^- 9 x 8 x 1 x 10^- 9)/0.04^2
F = 9 x 10^-5 N
There is an attraction
For trial 2,
q1 = - 4μC
q2 = 8μC
q1 = - 4 x 1 x 10^- 9 C
q2 = 8 x 1 x 10^- 9 C
F = (9 x 10^9 x 4 x 1 x 10^- 9 x 8 x 1 x 10^- 9)/0.04^2
F = 1.8 x 10^-4N
There is an attraction
For trial 3,
q1 = - 6μC
q2 = 8μC
q1 = - 6 x 1 x 10^- 9 C
q2 = 8 x 1 x 10^- 9 C
F = (9 x 10^9 x 6 x 1 x 10^- 9 x 8 x 1 x 10^- 9)/0.04^2
F = 2.7 x 10^-4N
There is an attraction
For trial 4,
q1 = - 8μC
q2 = 8μC
q1 = - 8 x 1 x 10^- 9 C
q2 = 8 x 1 x 10^- 9 C
F = (9 x 10^9 x 6 x 1 x 10^- 9 x 8 x 1 x 10^- 9)/0.04^2
F = 3.6 x 10^-4N
There is an attraction
The change in the value of the charge is proportional to the force