---
tags: [physics, electricity]
---

# Voltage sources

The following phenomena are the main sources that we use to generate voltage:

- friction
- magnetism
- chemicals
- light
- heat
- pressure

> In each case, energy in one state is transferred into energy as current. No
> energy is lost or gained, it simply changes its form.

### Magentism (electrical generators)

Magnetism is used as the voltage source in electrical generators and is 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.

#### 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](Cells_and_batteries.md). 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.

### Light (photovoltaic cells)

Solar energy can be converted to electrical energy through solar panels which
are large collections of **photovoltaic cells**.

When the surfaces of these cells are exposed to light, it dislodges electrons
from their orbits around the surface atoms of the cell material. For each cell
this only produces a very small amount of energy, therefore large quantities
must be used.
