How to understand Kirchhoff's current law? For any node or closed surface in any lumped parameter circuit, at any time, the algebraic sum of all branch currents passing through the node or closed surface is equal to zero

How to understand Kirchhoff's current law? For any node or closed surface in any lumped parameter circuit, at any time, the algebraic sum of all branch currents passing through the node or closed surface is equal to zero

Just like multiple inlet and outlet pipes, inlet and outlet are equal to zero

On the problem of circuit analysis! Kirchhoff's current law
What is a closed surface?
Is there a definition of closed surface? Can it be a closed surface with electronic components?

It's OK to circle any one, including the circuit you want to include. Kirchhoff's current law is applicable

What is the content of Kirchhoff's law?

KCl Kirchhoff's current law: the algebraic sum of the current flowing into the node is equal to 0
KVL Kirchhoff's law of voltage: the algebraic sum of all voltages in any circuit is equal to 0