Question

Two small conducting spheres of equal radius have charges +10microcoloumb and -20microcoloumb respectively and placed at a distance R from each other.They experience force F₁ if they are brought in contact and separated to the same distance, they experience force F₂ . Then the ratio of F₁ and F₂ will be?

Answer 1

as we know from coulomb law that the force acting between two bodies is proportional to the product of charges.

let the charges on the spheres initially be Q1 and Q2
and after the contact be Q3 and Q4
the distance will not matter in this case as it is same initially and finally and will get cancelled out in the ratio.

F1/F2 = (Q1 x Q2)/(Q3 x Q4)
Q1 = 10
Q2 = -20
after contact the charges on the spheres will become equal
from law of conservation of charge
Q3 + Q4 = Q1 + Q2
Q3 + Q4 = -10
but Q3 = Q4
so Q3 = Q4 = -5
we get F1/F2 = (10 x -20)/(-5 x -5) = -8