Update Unit_4_Physics_Study_Sheet.md

Grade 9/Science/SNC1DZ/Unit_4_Physics_Study_Sheet.md

@@ -266,7 +266,7 @@
 - The electric currnet is measured by an `ammeter`.
     - It is connected `in series` to the item you wnat to measure, which means you put the ammeter `infront or behind` the item you want to measure.
 
-### 3. Potential Difference / Voltageg
+### 3. Potential Difference / Voltage
 - the `difference` in electrical potential `energy` when a charge moved between `2 points` in an electric circuit.
 - **Symbol** for **Voltage**: `V`.
 - **Unit** for **Voltage**: `Volt[V]`
@@ -288,5 +288,21 @@
     - `Everything` has resistance. Conductor has low resistnace. Insulator has high resistance.
         - Example: wire has an resistnace so low that it is ignored in many calculations.
 
+## Product Efficiencies
+- Simply take the output / input x 100 and you get the percentage of the efficiency of your product.
 
+## Ohm's Law
+- Ohm's law states that $`V = IR`$, which means the volatage is equal to the current multiplied by the resistance.
+- When given a circuit, with one unknown value such as `I`, simply use Ohm's law to find the missing value.
 
+## Series Circuits
+- In a series circuit, there are a set of rules where the current, voltage, and resistance follow.
+- $`I_T = I_1 = I_2 = I_3 \cdots = I_N`$
+- $`V_T = V_1 + V_2 + V_3 \cdots + V_N`$
+- $`R_T = R_1 + R_2 + R_3 \cdots + R_N`$
+
+## Parallel Circuits
+- In a parallel circuit, there are also a set of rules where the current, voltage, and resistance follow. The current and voltage rules are swapped in this case.
+- $`I_T = I_1 + I_2 + I_3 \cdots + I_N`$
+- $`V_T = V_1 = V_2 = V_3 \cdots = V_N`$
+- $`R_T = (R_1 + R_2 + R_3 \cdots + R_N)^{-1}`$ (I think).