diff --git a/Grade 9/Science/SNC1DZ/Unit_4_Physics_Study_Sheet.md b/Grade 9/Science/SNC1DZ/Unit_4_Physics_Study_Sheet.md
index d88b0c1..4192a49 100644
--- a/Grade 9/Science/SNC1DZ/Unit_4_Physics_Study_Sheet.md	
+++ b/Grade 9/Science/SNC1DZ/Unit_4_Physics_Study_Sheet.md	
@@ -144,6 +144,8 @@
 - The negative charges go to the cloud and the postiive charges move to the top.
 - When the charges reunite, lightning will strike.
 
+<img src="http://www.physics-and-radio-electronics.com/blog/wp-content/uploads/2016/10/lightningbetweenuppercloudandground.png" width="500">
+
 ## Dangers / Applications of Electrostatics
 - **Dangers**:
     - Any sparks are small inginitions in places such as gas stations or oil refineries can cause fires and expolsions.
@@ -188,9 +190,17 @@
 
 ## Batteries
 - `Electrochemical Cell`: A package of chemicals that converts `chemical energy into electrical energy`.
-- `Battery`: More than 1 cell.
+- `Battery`: More than 1 cell / two or more electric cells in combination.
 - Types of cell: `dry` (paste, like a AA battery), `wet` (liquid, like a Car battery).
 
+### Electrical Cells
+- Device that converts chemical energy into electrical energy
+    - i.e. **portable devices (cameras, cellphones, flashlights)**
+- Consists of:
+    - 2 electrodes in a conducting solution (electrolyte)
+    - **Electrodes** = conductors (1 easily postively charged and the other easily negatively charged)
+- Electrons in the electrolyte are repelled by the negative electrode and attracted to the positive electrode
+
 ### 1. Wet Cell (Voltaic Cell)
 - <img src="https://files.catbox.moe/krm6sm.png" width="500">
 
@@ -200,8 +210,10 @@
 
 ### 3. Specialized Cells
 - **Fuel cell** 
-    - Generates using external fuel, works like an engine without a moing part, requires continous source of fuel and oxygen.
+    - Generates using external fuel, works like an engine without a moving part, requires continous source of fuel and oxygen.
+    - Operate far longer than a conventional electric cell
     - Generates `non-polluting` exhaust.
+    - I.e Hyrdogen fuel cell: produces electrical energy by converting hyrdogen and oxygen into water
     - **Uses**:
         - Primary and backup power for commerical industrial and residential buildings.
         - Power fuel-cell vehicles.