Electricity

Electricity

Electricity is used everywhere by almost everyone.  It is a form of energy that is easy to control and very flexible.  Most people don't know much about electricity other than how to use it.  What they do know is often anecdotal and wrong.  Government is currently making and changing regulations that will affect our use of electricity.  It is necessary to know the fundamentals in order to determine how the proposed changes will affect us and, more importantly, if they make sense.  Some of the changes proposed aren't as clear cut as they seem.  The intention of this web site is to explain the basics about electricity so that you can better understand way electricity works and why things are done the way they are.  Electricity is not magic.  It follows the laws of physics just like everything else in the universe. 

Danger from electricity is in two forms;  electrical shock and burns.  Electric shock occurs when a sufficient flow of electrons occurs through a body.  The shock hurts because it is making cells do things they aren't designed to do.  A strong enough shock can stop the heart which will kill you.   It can also cause violent convulsions which can cause physical damage.   Electricity can also cause burns.  The temperature of an electric arc is approximately 7,000 degrees farenheit or roughly the temperature of the photosphere of the Sun.  An electric arc is hotter then a welding torch.  Electrocution occurs when enough current flows through the body to interrupt normal operations.  As little as 10 milli-amps ( 10 one thousandths of an amp ) can cause fibrillation of the heart resulting in death.  Anything above that is very dangerous depending on circumstances.    If the source is household  electricity, 120 Volts, then 10 milli-amps is about 1 watt.  That's not much.  A single night lite is about 4 Watts.   Low voltage batteries below 48 volts are relatively safe as far as electric shock.  However a low voltage battery like a car battery has enough energy to burn a steel wrench in two.  Low voltage batteries and power supplies often have current ratings high enough to turn wire, rings, watches, etc. red hot, causing severe burns.   You should always be careful with electricity.  If you aren''t absolutely certain that it's safe then it should be considered dangerous.  

Electricity is invisible.  You can't see it or smell it.  It is helpful but it can also be dangerous.  Electricity is a tool and like any tool it works best when you understand it and it can be dangerous and destructive if it's misused.

All forms of electricity are measured in the same units.   Voltage, Current (amps) and Power in Watts. 

Terminology:
Voltage is referred to as "E" (capital letter e) and measured in Volts.  It is the force that causes electrons to move. 
Current is referred to as "I" (capital letter i) and measured in Amps.  
Resistance is referred to as "R" and measured in Ohms. 
Power is referred to as "P" and measured in Watts

Electricity is the flow of electrons from the negative side of a source to the positive side.   The quantity of electrons flowing is the current (Amps).  Charge is measured in Coulombs.  One Coulomb is equal to 6.25 x 10 to the 18th
or 6,250,000,000,000,000,000 electrons per second through a given point.

1 Amp is equal to one Coulomb per second at a Voltage of 1 Volt.
1 Volt is the electrostatic charge needed to cause 1 Amp of current to flow in a circuit with a resistance of 1 Ohm.
1 Amp at 1 Volt is equal to 1 Watt of power.

The variables described above apply to both DC and AC circuits. 

.We can compare electricity to water to make it easier to understand.  Voltage is similar to pressure in a water system.  Electrons are similar to water.  They both flow when pressure is applied.  If you  increase water pressure then more water flows.  Likewise if you increase Voltage more electrons flow.  Decrease either and the flow decreases. 

In order to use Electricity for anything it must do work.  The ability to do work is Power which is measured in Watts.  750 Watts is approximately 1 horsepower.  A Watt is an instantaneous amount of power.  To do work we need power for a period of time long enough to do the work.  The power over time is measured in Watt Hours.  One Watt Hour is one Watt for one Hour.   We use a lot of power so you often see power usage referred to in KWH which is Kilo Watt Hours.  Kile mean 1,000 (one thousand).  1 KWH is 1,000 Watts for 1 hour.

Sources of electricity:

The most common source of DC electricity is batteries.  A battery is made up of cells.  Each cell is limited in voltage due to chemistry.  The small batteries used in flashlights and toys are called "Dry Cells".  There are several types and they usually have a voltage of 1.25 to 1.5 Volts DC depending on the type.  1.5 Volts is the most common.  These cells are connected together and put in one package to make a battery.  A 6 volt battery has 4 cells.  4 times 1.5 Volts = 6.0 Volts.  A 9 volt battery has 6 cells.  6 * 1.5 = 9.   

Car batteries are call "wet cells" because they contain a liquid (electrolyte).  The liquid in a car battery is sulfuric acid.  Most wet cells produce 2 volts.   A 12 volt car battery has 6 cells.  Wet cells store more energy then dry cells so they are bigger.  The electrolyte (sulfuric acid) makes them hazardous

Types of Electricity

There are two kinds of electricity; AC and DC.  AC means Alternating Current.  The wall plug in a house provides AC.  DC is Direct Current.  Batteries provide DC.  The two are different in that DC has a constant voltage and AC has a constantly changing voltage. 

If you look at the instantaneous DC voltage you will see that it doesn't change  If you look at the instantaneous voltage on an AC circuit, like the wall socket in the house, you will see that it changes constantly from zero to a high value then back through zero to an equivalent negative value then back to zero.  For home power it does this 60 times per second

Circuit Types

There are two basic types of circuits: Series and Parallel.

Note that batteries are made of cells connected together to produce the desired voltage.  That type of connection is called a "series circuit" because it connects things in a series.   Series circuits allow us to 4 1/2 Volt cells to make a 6 Volt battery.  If we connected 8 1 1/2 Volt cells we would make a 12 Volt battery.

The other primary type of circuit is the parallel circuit.  To connect two cells in parallel we would connect both cells negative terminals together then connect both positive terminals together.    The voltage across the cells would be the same as the voltage acrouss one cell.  The maximum current supplied by the two cells would be twice as much as for one cell.  We would use that when the load was too high for one cell.   We can also use that to provide twice as much Power for a given time or the same amount of power for twice as long as one cell.

We put cells in prallel to increase the power capacity.  Two cells = twice the capacity,  three cells = 3 times the capacity. 
For example:  We have a battery operated light that last for 4 hours before the battery goes dead but we need the light to stay on for 8  hours.   We can do that by adding another battery of the same type in parallel to the existing battery.  If we want the light to stay on for 12 hours then we can connect a third battery in parallel to the two existing batteries.   

Voltage is increased by connecting cells in series. 
Power capacity is increaded by connecting cells or batteries in parallel. .

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