Electricity is everywhere in our lives. It lights our homes, cooks our dinners, and powers our televisions, hair dryers, and many other electronic devices.

Electricity, http://www.energyquest.ca.gov/story/chapter02.html or electric current, is the flow of charge.
The study of charges in motion is called electrodynamics. FYI…The study of charges that do not involve moving charges or current is called electrostatics. http://www.clean.ns.ca/images/SMBEE/electricity-pic.jpg

Charge can either be positive or negative. Any two like charges, for example two positive charges, will repel one another. Opposite charges attract. I’m sure you’ve heard of the old phrase “opposites attract!”
Opposite charges attract one another.
Electricity acts differently through different materials. Electricity can easily flow with little resistance through a conductor.  Metals are good conductors of electricity.

Electric current does not flow easily through an insulator. Ceramics and plastics are good insulators since they do not conduct electricity.

A semiconductor  will allow electric current to flow but with some resistance. They only conduct electricity under certain circumstances. Silicon is a good semiconductor.

Superconductors allow current to flow with no resistance. These are not common and have only been produced in extreme laboratory conditions. Magnetic levitation is an application where superconductors can make trains almost float on strong superconducting magnets. It eliminates friction between the train and its tracks. A Japanese magnetically levitated train traveled at a speed of 321 mi/h in 1979 using superconducting magnets on board the train.

The magnets induce currents in the rails below which cause a repulsion suspending the train above the track. Mercury was historically the first element to show this level of conductivity.

When a conductor, like copper, is connected between the two terminals of an energy source, like a battery, and an appliance it forms an electric circuit.

In order to make a circuit, there must be a complete, unbroken loop connecting one terminal to the other.

A battery in a circuit will cause charge to flow from one terminal to another creating the electric current. The electric current from batteries keeps our cars running and makes our flashlights shine in the dark.

Electric current is the amount of charge, q, passing a given point in a certain amount of time. The amount of current, (I) flowing is measured in Amperes (A) or amps named after the French physicist André Ampere (1775-1836).

Current can be calculated from the following equation:

where I is the current, q is the charge measured in Coulombs and t is the time.

Example:
A 2.5A current flows through a wire connecting the terminals of a battery. After 4 minutes, how much charge has passed through the circuit?

FYI…0.1 amps of current flowing between your hands across your heart is enough to kill you!

The amount of current flowing in a circuit depends on the voltage and resistance. Voltage or electric potential is the pumping power of the current. It is measured in volts, named after a physicist named Volta.

Most small batteries like a C battery are 1.5V and car batteries are 12V.
 

High voltage lines have thousands of volts between them.

Resistance, (R) is a measure of how the material of the conductor resists the motion of electrons. It is measured in ohm’s, and represented by the Greek letter, omega, .

The resistance of a cylindrical resistor increases if its length increases, its cross-sectional area decreases, its temperature increases, and is dependent on what the material is made of or its resistivity.

You can find the resistivity constant for most materials you will encounter at the link below:

http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/rstiv.html#c1

Resistance varies for different materials. Gold, silver and copper have low resistance because current can flow easily through these materials. This makes them good conductors. Aluminum, glass and wood have high resistance since current cannot pass through these materials easily. They are not good conductors.

Imagine your house gets flooded and you have to use a water pump to get the water out. The first water pump you use has a very thin hose. You find that it does not pump water out very quickly so you try a wider hose. The wider hose pumps out more water faster.

The water pump can be compared to the voltage. The water pump provides the pumping power of the water just like the voltage provides pumping power to push the electrons through a wire. The flowing water can be compared to the current. A little water flowing through the hose is like a little current flowing through the wire. The hose diameter can be compared to the wire’s resistance. A thin hose let’s only a little water through, just like a poor conductor with high resistance only lets a little current through.

Experiments

Try these experiments!

Make yourself a human battery!
http://www.spartechsoftware.com/reeko/Experiments/ExpHumanBattery.htm