Find Zero Field Location of Two Charges of q1=4μC and q2=-1μC

[hacker804]

Homework Statement

Two charges of q1=4μC and q2=-1μC are separted by a distance of 3 m.Find and justify the zero field location.

Homework Equations

E=\frac{kQ}{r^{2}}

The Attempt at a Solution

Consider a point x to the right of charge q1 where the field is zero.The distance of x from q1 is x and from q2 is 3+x.
I solved the problem and the answer comes out as -6m.The answer given by the book is 3m.Is my answer correct??

Thanks

 

[voko]

You and the book should agree on how the charges are located and from which point the distance is measured.

 

[ehild]

Homework Statement

Two charges of q1=4μC and q2=-1μC are separted by a distance of 3 m.Find and justify the zero field location.

Homework Equations

E=\frac{kQ}{r^{2}}

The Attempt at a Solution

Consider a point x to the right of charge q1 where the field is zero.The distance of x from q1 is x and from q2 is 3+x.
I solved the problem and the answer comes out as -6m.The answer given by the book is 3m.Is my answer correct??

Thanks

No, your answer is not correct. If the point in question is at distance x to the right from q1, a negative value means that it is on the left, and it is impossible. Perhaps, you will show your work in detail.


ehild

 

[hacker804]

So it is 6m to the left from q1 which means it is not on the line between the two charges which is only 3m.

 

[LeonhardEu]

First of all there are two such positions, one between the charges and one outside from the side of the smallest. The two positions come from the dependence of E from x squared ( or only by physics as we like, as you go close to q2<q1 the field of q2 becomes stronger. In other cases the field of the bigger charge is bigger than that of q2. But you can go from both sides. So there are two such points). Just find the expression of E at any location in the line of the two charges and solve E = 0 for x. Your book finds the distance of the point from q2.