What is the concept of closed boundary in Circuit theory ?
Lets take an example of KCL.A kcl also applies to a closed boundary.This may be regarded as a generalized case because a node may be regarded as a closed surface shrunk to a point.In two dimensions,a CLOSED boundary is the same as a closed path.The total current entering the closed surface is equal to the total current leaving the surface.You may refer to various videos available on YouTube to get your concept more cleared.