How Does Changing Distance Affect Force Between Charges?

[dummie90]

Homework Statement

By what factor must you change the distance between two point charges to change the force between them by a factor of ten?

Homework Equations

F1=kq1/r^2
F2=kq2/r^2

The Attempt at a Solution

F1:F2= 10
r1/r2=sq.root(F2/F1)= 1/sqroot10

I do not understand how to get to r1/r2=sq.root(F2/F1)= 1/sqroot10
I do understand that you square root F2/F1 to get rid of the square of r. but why is F2 on top of the fraction instead of F1 (i.e. sqroot F1/F2) and how does that become 1/sqroot 10? And how did that equation even come about?

Sorry I'm very confused I've tried to make sense of this worked example many times,
Thank you so much for the help

 

[tiny-tim]

Welcome to PF!

F1=kq1/r^2
F2=kq2/r^2
…
Sorry I'm very confused …

Hi dummie90! Welcome to PF!

(have a square-root: √ )

You're very confused because your equations are wrong.

They should be:

F₁=kqQ/r₁^2
F₂=kqQ/r₂^2

now can you see how it comes out as √(F₂/F₁)?