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NATURE.M
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Homework Statement
Two line charges, of length L/2 and carrying equal and opposite charge density ±λ, are placed on the x-axis so that their ends just touch at the origin, as shown in Figure 1. They are separated by an insulating material with negligible width.
a. Find the magnitude and the direction of the electric fields at points P and P′. P is a point on the y-axis at (0, b), and P′ is a point on the x-axis: (a, 0). Assume b>>L/2
b.Find the electric dipole moment of this line charge system.
The Attempt at a Solution
a. So basically I solved the problem but was a bit confused about the signs.
At point P: For the line charge on the left of the origin, taking differential elements of charge we have dq = -λdx. If my understanding is correct, then the electric field vector at P would be directed towards the line charge, and so the x and y components of electric force point in the negative direction. And so the x and y components of dE are positive. Now, I am considering one to many negative signs? So really I'm just a bit confused about how to treat [itex]\pm[/itex][itex]\lambda[/itex].
Intuitively, if you consider the other line charge on the right of the origin the electric field vector it generates at P should be directed away from the line charge.
But after taking the integral from -L/2 to 0 for the electric field generated by the first line charge, and then taking the integral from 0 to L/2 for the electric field generated by the second line charge, and using b>>L/2, the x component of electric field reduced to ≈0 and the y component is given by: [itex]\frac{λL}{4\pi\epsilon_{0}b^{2}}[/itex]. This seems reasonable, but I'm unsure If I got all the signs right as expressed in my previous mark.
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