diff --git a/docs/1b/ece140.md b/docs/1b/ece140.md
index 73d2a5a..9decd5d 100644
--- a/docs/1b/ece140.md
+++ b/docs/1b/ece140.md
@@ -149,3 +149,14 @@ $$\text{output}\propto\text{input}+C$$
 
 !!! example
     Halving voltage must halve current (or at least halve it relative to a base current / voltage).
+
+### Superposition
+
+In linear circuits, the superposition principle states that the voltage/current through an element is equal to the sum of the voltages/currents from each independent source alone.
+
+$$
+v=\sum v_x \\
+i=\sum i_x
+$$
+
+To do so, each unused independent source should be replaced with a short circuit (voltage) or an open circuit (current).