Net electric field by two curved rods

AI Thread Summary
The discussion revolves around determining the direction of the electric field at the midpoint between two positively charged curved rods. Initially, it was believed that the electric field would point upward due to the extra length of the lower rod. However, the consensus is that the electric field actually points downward. This is because the electric field contributions from the top sections of the rods cancel each other out, leaving only the lower segments to influence the field direction. The reasoning highlights the importance of considering the geometry and distribution of charge in electric field calculations.
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Homework Statement



http://online.physics.uiuc.edu/cgi/courses/shell/common/showme.pl?courses/phys212/oldexams/exam1/sp08/fig4.gif

Two curved rods each have charge +Q uniformly distributed over their length. Which statement best describes the electric field due to these two rods at the midpoint between the two rods marked by an X ?

(a) E points up.
(b) E points down.
(c) E = 0.

Homework Equations



It's more like geometry I think.

The Attempt at a Solution



I definitely thought E would point up since the rod at the bottom has extra length that has positive charge, which would affect electric field to the radially outward direction. But the answer is b, E points down. Could anyone explain the reason? Thanks in advance.
 
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E should point up. If your problem statement and diagram are accurate, then the answer is wrong. The top section should cancel out exactly with the segment of the bottom rod that is directly opposite. This leaves two portions of the bottom rod to contribute to the direction of the field.
 
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