diff --git a/education/physics/PHYS2220/Electric Charge.md b/education/physics/PHYS2220/Electric Charge.md
index a6204c4..27464fe 100644
--- a/education/physics/PHYS2220/Electric Charge.md	
+++ b/education/physics/PHYS2220/Electric Charge.md	
@@ -30,3 +30,6 @@ An electric dipole consists of two point charges of equal magnitude but opposite
 - The dipole field at large distances decreases as the inverse *cube* of the distance. This is because the dipole has zero *net* charge.
 
 # Continuous Charge Distributions
+It's largely impossible to sum the electric field from every particle in a piece of matter, so the approximation is made that the charge is spread continuously over the distribution.
+- If the charge distribution extends throughout a 3d volume, we describe it in terms of the **volume charge density** $\rho$, with units of $\frac{C}{m^3}$. 
+- For charge distributions spread over surf
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