The defintion of Electric Current is simply the flow of protons (positive charges) or the flow of electrons (negative charges). Many people use a river as an analogy to describe electric current
As you can see in the picture of a river above, the flow of water down the river represents Electric Current. If electric current were to increase, it is like the amount of water increasing in a river.
A little tid bit on... Conventional Current: Conventional current can be defined as just the flow of positive charge.
Why electric current flows:
There is a flow of charges (There is an electric current) when there is a force pushing it. In the case of electric current, this force is known as voltage. Voltage is what makes it possible for current to move. Using the same river analgy as before, voltage corresponds to the river drop. The downhill drop in the river makes the water move; the voltage makes the water move.
CONDUCTORS AND INSULATORSEdit
A conductor is what electric current flows through. An example of a conductor is a copper wire. http://web.archive.org/web/20050714140210/http://oldsite.vislab.usyd.edu.au/photonics/revolution/technology/images/copper_wire.jpg Conductivity (how easily the electric current flows through the conductor) is measured by how many free or loose electrons there are jumping from atom to atom within a conductor.
A rule to remember: Small # of free electrons = bad conductivity = more resistance! Large # of free electrons = good conductivity = less resistance!
Insulators are objects that do not conduct electricty. Therefore, there is no electric current present in insulators. An example of an insulator is a plastic cup. http://web.archive.org/web/20031125121424/http://www.instawares.com/products/p/ppi-16-x.jpg If you want current to flow, do not use an insulator!!
A little tid bit on Mr. Ohm!:
In 1827, Georg Simon Ohm, a German physicist, discovered that voltage depended on the electric current and the resistance. This relationship became known as Ohm's law.
I = V/R In Ohm's law, I stands for current, which is measured in Amperes (A). It can also be measured in c/s which is coulomb per second. 1 coulomb per second is equal to 1 ampere, a.k.a. an amp!
If you look at the equation above, you can tell that the current is directly proportional to the voltage, V. In other words, as voltage goes up, so does current!
You can also tell that current is indirectly proportional the the resistance, labeled R. In Other words, as the flow of electrons increases, the resistance decreases! I don't have a graph for this, but you get the idea :)!
Let's Get Some Practice!Edit
Solve this problem using Ohm's Law: A battery creates a voltage of 15 volts that goes through a wire. If there is 3ohms of resistance (ohms is the unit resistance is measured in), how much current is flowing through the wire? What to Do:
15v = I(3ohms)
15v/3ohms = I
I = 5A
Current density is the amount of flow per square meter. It is measured in the unit j.
Sources Used Edit
Challoner, J. The Visual Dictionary Of Physics. New York: DK Publishing Inc., 1995.
"Current." Absoulte Astronomy Reference. 7 June 2006. http://www.absoluteastronomy.com/enc3/current_electricity.
Rosenberg, Paul. Practical Electricity. USA: Wiley Publishing Inc., 2004.
"The World Book Encyclopedia." Chicago: World Book, Inc.,1992.
Zitzewitz, Paul W. Physics: Principles and Problems. Columbus, OH: The McGraw-Hill Companies, Inc., 1999.
Pictures Used Sources Edit
Plastic Cup Picture: http://www.getimmediate.com
River Picture: http://www.scenesofvermont.com
Copper Wire Picture: http://oldsite.vislab.usyd.edu.au
Graph Picture: http://www.gcse.com