Can a Third Charge Achieve Zero Potential Between Two Unequal Charges?

[jaejoon89]

Homework Statement

If you bring 2 charges, Q_1 (=+6 micro Coulombs) and Q_2 (= -2 micro Coulombs), from infinity to positions on the x-axis of x = -4 cm and 4 cm, respectively, is it possible to bring a 3rd charge Q_3 ( = +3 micro Coulombs) from infinity to a point on the x-axis between the charges where the potential is 0? If it is possible, where would this be on the x axis?
a) It is not possible.
b) x = 0 cm
c) x = +2 cm
d) x = +6 cm
e) x = +1.5 cm

Homework Equations

V = kq/r

The Attempt at a Solution

Is it asking to find the null V point btwn the 2 charges (regardless of the 3rd charge)? Or the 3-point null?

 

[granpa]

we know there is a point between them with zero potential. what does it mean 'bring from infinity'? is it asking whether there is a line of zero potential extending from the point between them to infinity? or am I making it more complicated than it is?

 

[jaejoon89]

I'm not sure. That's just what the question says... Does it depend at all on the third charge?

 

[granpa]

no. the potential seen and felt by the third charge is the same as the potential without the third charge.

the third charge would change the overall potential but if it is a point charge then the potential becomes infinite at the position where the charge is at so it can't be asking that.

 

[granpa]

r1+r2=8

 

[granpa]

if the charges were equal it would be