Electric field strength between two points.

1. The problem statement, all variables and given/known data
Find the electric field strength at point P, which is located midway between charges A and B. The charges are separated by 20 cm. The first charge has a charge of 20 micro coulombs. The second charge has a charge of -30 micro coulombs.

2. Relevant equations
Electric field strength E=Kq/r K is coulomb's constant 9x10 raised to the ninth power. Q is charge. Ris distance from charge.

3. The attempt at a solution
I'm not sure where to start. You need the charge at point P to use Coulomb's law.
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 Hi. You don't need the charge at the point P. As you well said, the formula for electric Field is E=kQ/R. Only one charge appears there and it is the charge that produces the field. You are probably confused with Coulomb's law that says the force excerted by a charge Q on a charge q is F=kqQ/R. Since F=q E then E=kQ/R. So you don't need to know the charge at the point P.
 Ok so then what do i plug into the equation?

Electric field strength between two points.

You have two sources of the field. You can determine the field generated by each one. But you need to know the combined field at a given point. How could you do that?
 So i get the field of both and combine them?
 Yes, but the field is directional. You need to take this into account when you combine!
 Thank you!

 Tags elecrostatics, electric fields

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