ece140: add kirchhoff final

docs/1b/ece140.md

@@ -100,9 +100,17 @@ P &= IR^2 \\
 \end{align*}
 $$
 
-## Kirchoff's laws
+## Kirchhoff's laws
 
 !!! definition
     - A **node** is any point in the circuit to which 3+ elements are *directly* connected (i.e., all junctions).
     - A **supernode** is any connected group in the circuit to which 3+ elements are *directly* connected.
     - A **loop** is any closed path of elements.
+
+Kirchhoff's **current law** states that the sum of all current entering a node must be zero, where positive indicates current entrance.
+
+$$\sum i_\text{entering node}=0$$
+
+Kirchoff's **voltage law** states that the sum of all voltage in a **closed loop** must be zero.
+
+$$\sum v_\text{loop}=0$$