Electricity Basics

We???re not going to dig too deeply into definitions and equations here but to get to grips with the nature of electricity, we need to learn a little bit about what an atom is. All elements, such as copper and gold, are made up of atoms. Atoms in turn are made up of particles: protons (p), neutrons and electrons (e).

Protons & Electrons

In the simplest terms electrons are the smallest units of electricity. Protons & electrons have equal and opposite charges; electrons being negative and protons being positive. Like charges repel each other, unlike charges attract each other. ??The visual representation of the attraction between protons & electrons is similar to that of magnets clicking together when we hold the opposite poles toward each other. While protons are fairly static, electrons like to move about. A good example of this is lightning which is when electrons travel between the clouds and the ground.

Moving the Electron

We???ve learned that electrons like to get about, but in order for them to be able to move from one place to another, they need a medium and this is where conductors come in. Just like we use bikes to get from A to B, electrons use electrical conductors. Conductors, such as copper and aluminium wire, allow electrons to move about within their structures when a charge difference is created across two parts of the material. If there is no difference between two points in the circuit then there will be no current.

Charge (Q), measured in coulombs, is the number of electrons that can be found in whatever metal we’re dealing with. The flow rate (just like you’d find in a river) of this charge is what we call electrical current (I), which is measured in amperes or amps i.e. 1 amp exists in a circuit when one coulomb of charge is passing a point every second.

Voltage or Potential

In the earlier section we mentioned charge difference, meaning a force that will push electrons from one place to another. This force is called voltage and it is measured in volts (V). If we use a water system as an analogy, then if we increase the pressure in the system then more water will flow through our pipe per minute. The same thing happens in our electrical circuit, the higher the voltage then the greater the current in the wires.

The Essential Mix

Once we combine electrons, conductor and voltage, we can create an electric current in a form the we can actually use. Electricity is created when voltage pushes an electric current through a conductor. Both conductors and voltage have an effect on how current flows through a wire:

-???? increasing voltage increases the number of electrons flowing through a wire at any given time, leading to a greater current. If we think about our water system again then by increasing the water pressure, you increase the amount of water flowing through your pipe.

-???? increasing the diameter of our conductor allows more electrons to flow through for a given voltage, therefore producing greater electric current. This would be similar to using bigger pipes in our water system, so that we can use the same pressure but still get more water flowing through the system.

Power

Now we have electricity, we can use it to power devices to produce sound, light, motion etc. For example, applying electrical current to a DC motor will cause its shaft to spin. Power basically measures the amount of work that an electric current does when running through a device or appliance. E.g. work needed to heat a filament in a light bulb is 60 watts. Power is measured in Watts (W). One watt is equal to one joule of energy per second (joule meaning unit of work or energy). So if one joule of energy is expended in one second then the power is one watt.

The electrical power of a device is the product of voltage across it multiplied by the current through it:

POWER = VOLTAGE X CURRENT

W = V X A


Resistance

Resistance is the opposition to a current and is measured in ohms. Resistance always results in the conversion of electrical energy into heat. All conductors, have some kind of resistance, and represents a waste of energy or a loss to the system. Resistance in a wire depends upon the type of metal, length of the wire and the diameter of the wire.


Currents that you may come across

-???? DC (Direct current) is a simpler type of electricity and is unidirectional flow of electric charge. In simplified terms in a DC circuit, the current flows at a specific, constant voltage. This type of electricity can be produced by batteries, solar cells and dynamo type machine such as bike power generator. When we???re using a torch, pocket radio, portable CD player or virtually any other type of portable or battery-powered device, we???re using direct current.

-???? AC Alternating current) is type of current whose direction reverses in cycles. The back-and-forth motion occurs between 50 and 60 times per second, depending on the electrical system of the country. Due to this cyclical motion, the voltage in AC current alternates. AC is the type of current that is delivered to our homes and businesses and we use it to power all of our appliances.

Know your revolutions

Revolutions per minute (rpm, RPM, r/min, or r??min???1) is a unit of frequency. It simply means the number of full rotations completed in one minute around a fixed axis. It is most commonly used as a measure of rotational speed of some mechanical component, in our case the bicycle wheel.

For more information check out these books:

Off The Grid, Managing independent renewable electrical systems ??? Duncan Kerridge,

CAT Publications, ISBN: 978-1-902175-56-0

Advanced Electrical Installations ??? C Shelton, Addison Welsey Longman, ISBN: 0-582-24618-0

Electronics for Dummies ??? Gordon McComb & Earl Boysen, Wiley Publishing, ISBN: 0-7645-7660-7

The 12 Volt Bible For Boats ??? Miner Brotherton, McGraw-Hill, ISBN: 0-07-139233-5

Page last updated on December 4, 2009 at 12:36 am