Calculate the ratio q1/q2 of the two charges

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Homework Help Overview

The problem involves calculating the ratio of two electric charges, q1 and q2, based on their distances from a point where the electric potential is zero. The context is within electrostatics, specifically dealing with electric potential and charge interactions.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to relate the charges and their distances using the formula for electric potential. Some participants question the sign of the charges and the conditions for the potentials to cancel at point A.

Discussion Status

Participants are exploring the implications of the potential being zero at point A and discussing the need for one charge to be negative to achieve this condition. Guidance has been offered regarding the correct formulation of the potential equations.

Contextual Notes

There is an assumption that the charges may have different signs, which is under discussion. The original poster's calculations led to a positive ratio, but the context suggests a need for a negative value, indicating a potential misunderstanding of charge signs.

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Homework Statement


Charge q1 is 0.16 m from point A. Charge q2 is 0.40 m from point A. The electric potential at A is zero. Calculate the ratio q1/q2 of the two charges.


Homework Equations


V= kq/r


The Attempt at a Solution


I did
kq1/r1 = kq2/r2
q1/q2 = r1/r2
q1/q2 = 0.16/0.40
q1/q2 = 0.40
My magnitude is right, but the answer is a negative, -0.40. What am i doing wrong?
 
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You need the potentials to cancel out at A. Since potential is a scalar, you want the potential from one to be positive at A, ad the potential from the other at A to be the negative of the first at A, so they will add to zero. So, assume one charge is negative and put the negative sign in there. That is why your sign is off.

Your initial equation should read:

[tex]\frac{KQ_1}{r_1}=-\frac{KQ_2}{r_2}[/tex]Does this help?
 
So does that mean that my initial equation is:
Vt=V1 + V2? So that when i make the Vt=0, the equation will read V1=-V2?
 
Yes,
[tex]V_A = V_1+V_2[/tex]

But we want the potential at A equal to zero so:

[tex]V_A = V_1+V_2=0[/tex]

[tex]V_1=-V_2[/tex]
 
that helps a lot! thank you very much! :D
 
No Problem!
 

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