# Two point charges

I was wondering if someone could help me with my posted problem. All the necessary details from the template are included in the screenshot on the right.

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gneill
Mentor
From the second attachment (the one on the right) it looks as though you need only cross multiply and solve for x to finish.

I don't know how to do so mathematically...

rude man
Homework Helper
Gold Member

Draw a picture of the two charges along a line, then equate Coulomb attraction of a unit (positive) test charge to qB to repulsion of that test charge from qA.

Hint: the zero-field point might be between qA and qB, or it might not ...

Coulomb's law is not used. My professor said to only use the E=k[q]/rsquared formula...

I know that the order of the point charges goes as followed

qb -------------------qa--------------------P

rude man
Homework Helper
Gold Member
I know that the order of the point charges goes as followed

qb -------------------qa--------------------P

Never mind, you called x the distance from p to qB and d the distance between qA and qB, so what you wrote is fine.

gneill
Mentor
I don't know how to do so mathematically...

Really?

If ##\frac{a}{b} = \frac{c}{d}## then ##a \cdot d = b \cdot c##

You've never seen this?