
#1
Feb813, 03:52 PM

P: 746

Hello,
I am looking at an example of finding the charge of a uniform disk with a continuous charge on the surface. They go about the problem by finding the infinitesimal charge of concentric rings dq = σdA = σ(2πr dr) The part I don't understand is that they use the area as 2πr dr? The area of a ring would be ∏(R2^2  R1^2), right? 



#2
Feb813, 04:05 PM

Mentor
P: 11,235





#3
Feb813, 04:14 PM

P: 746

Ok I just calculated it and now I see. The book didn't even bother to explain that approximation, which left me confused. Thank you for clearing that up so quickly =)



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