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darkpsi
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Homework Statement
Find the electric field a distance z above the midpoint of a straight line segment of length
2L, which carries a uniform line charge λ.
Homework Equations
1) my textbook says :
E(r) = 1/4πεo ∫V λ(r')/r2 r dl'
2) and this also works? :
E(r) = 1/4πεo ∫V λ(r')/r3 r dl'
both where r is the unit vector from the charge to the point we are caluclating the field at
The Attempt at a Solution
I can integrate once I get the setup down just fine. I just wanted to know when and why this two are the same. For example, in my book it says for the setup for this problem :
E(r) = 2 * 1/4πεo ∫V(λdx/r2)cosθz
For one thing, how did that cos appear and since it equals z/r couldn't 2) have just been used from the start? And if 2) can be used could I apply it to surface and volume integrals?