- #1

member 392791

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?