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exitwound
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Homework Statement
http://scitec.uwichill.edu.bb/cmp/online/P10D/Hunte/Electric%20fields_files/image122.jpg
Find the Electric Field at Point P at height z over a uniformly charged disc of radius a with uniform charge Q.
Homework Equations
The Attempt at a Solution
I'm looking at the solution online, on multiple sites, only to be stuck with the very first step.
Why on Earth is [tex]dA=2\pi*r*dr[/tex] and what exactly is dA?