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+---
+categories:
+  - Electronics
+tags: [physics, electricity, electromagnetism]
+---
+
+# Electromagnetism
+
+// TODO: Add explanation of the relationship between electricity and magnetism and the underlying physics.
diff --git a/Electronics/Physics_of_electricity/Voltage.md b/Electronics/Physics_of_electricity/Voltage.md
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 tags: [physics, electricity]
 ---
 
-# Voltage 
+# Voltage
+
+## Difference of potential and the tranfer of energy
+
+We noted in the discussion of [current](/Electronics/Physics_of_electricity/Current.md) that current flows when there is difference of potential between two points with negatively charged atoms at one point and positively charged atoms at the other.
+
+'Difference of potential' is the same thing as voltage. We use the term 'voltage' to denote the potential for current to flow. Voltage is essential to current because it is the force that enables the current to flow.
+
+Without voltage there can be no current because in their natural state, the electrons in an atom are in random motion with no direction. To produce a current energy must be imparted to the electrons so that they all flow in the same direction.
+
+Voltage is the application of this energy. Any form of energy that dislodges electrons from atoms can be used to produce current.
+
+> It is important to realise that in this process energy is not 'created', rather there is a transfer of energy from one form to another. The force applied to generate the current is energy in one form that is converted to another form: electrical current.
+
+## Voltage sources
+
+The following are the main sources of voltage:
+
+- friction
+- magnetism
+- chemicals
+- light
+- heat
+- pressure
+
+Energy in these states can be transformed into energy as current. We will review the most common sources below.
+
+### Magentism (electrical generators)
+
+Magnetism is used the voltage source in electrical generators by far the most common method of producing powerful and large currents at scale.
+
+If a conductive wire is passed through a magnetic field voltage will be produced so long as there is motion between the magnetic field and the conductor. A **generator** is a device that generates current in this manner. Generators themselves need to be powered. They can be powered by steam from a nuclear power plant, water, wind, coal or other fossil fuels.
+
+// TODO: Add symbol
+
+#### AC/DC
+
+Depending on how it is wired, a generator can produce **directed current** (DC) or **alternating current** (AC):
+
+- **Directed current**
+
+  - The electrons flow in only one direction
+
+- **Alternating current**
+  - The electrons flow in one direction and then the other
+
+### Chemicals (cells and batteries)
+
+The chemical creation of current is the physics behind batteries. Chemical current production produces currents on a smaller and less industrial scale than generators.
+
+A chemical cell consists in two dissimilar metals such as copper and zinc. We call these the **electrodes**. They are immersed in a salt, acid or alkaline solution. We call these the **electrolytes**. The electrolyte pulls the free electrons from the copper electrode which leaves it imbalanced with a positive charge. The zinc electrode attracts the free electrons from the electrolyte giving it a negative charge, thus a difference of potential is achieved.
+
+// TODO: Add symbol
+
+### Light (photovoltaic cells)
+
+// TODO: Add symbol