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Ohm's Law:
Ohm's Law is a systematic way of calculating the potential difference across a circuit using three variables: E (or V), the potential difference; I, the current of the circuit; and R, the total resistance of the circuit. E is measured in volts (V), I is measured in amperes (A), and R is measured in ohms (Ω).

The total potential difference of a circuit is equal to the product of the the total current and the total resistance in that same circuit: V = IR

The formula can also be algebraically rearranged to show that current is directly related to the potential difference and inversely related to the resistance: I = V/R

Ohm's Law was named after physicist George Ohm, who published a variation of the formula we see today in 1827. Ohm’s law is applied daily by electric engineers in the calculations of circuits that are being built. It allows for the calculation of the needed resistance to pass a certain current through a circuit with a particular voltage.

This video will provide you with a quick and simple way of remembering and utilizing Ohm’s Law:




References:
1) Ohm's Law - http://en.wikipedia.org/wiki/Ohm's_law
2) Ohm's Law Demo Video - http://youtube.com/watch?v=_-jX3dezzMg


Resistance:
Resistance is defined as "the opposition of a body or substance to current passing through it, resulting in a change of electrical energy into heat or another form of energy" (Ref. 1). It is an independent varible of a circuit, which means it does not depend on the amount of current or voltage flowing through the circuit. The SI unit for resistances is ohms, represented by Ω. When resistance is added to a circuit, it “determines the amount of current through the object for a given voltage across the object” (Ref. 2).

Resistance can be caused by a variety of materials: metals, semiconductors, insulators, and ionic liquids produce resistance.

References:
1) Definition of Electrical Resistance - http://dictionary.reference.com/browse/resistance
2) Electrical Resistance - http://en.wikipedia.org/wiki/Electrical_resistance


Current:
Current is the continuous flow of electrons through a circuit. The electrons continue to flow in the same direction as long as the source is pushing the electrons in that direction. There are two types of current, direct current and alternating current. In direct current, the electrons more in one continuous direction. However, in alternating current, the direction of the current switches back and forth. Electric current is made up of electrons that are flowing together and all at once through a conductor. These electrons keep moving and thusly are pushing the electrons ahead of them. Therefore, if there is a break at any point in the circuit, the electric current will cease its continuity.



References:
1) Current -http://www.allaboutcircuits.com/vol_1/chpt_1/4.html

Alternating Current:
Alternating current is present when the direction in which the current flows in the circuit is constantly being reversed back and forth, unlike direct current in which current only flows in one direction. Alternating current is commonly referred to as AC and is the most commonly sent form of current out from electrical power plants. Therefore, AC can be found in your house and usually the current is switching back and forth 60 times each second. Or in other words, the current switches at 60 hertz. AC is more prevalent to DC and won out the Electric War because AC can be sent long distances due to its high voltage and therefore AC was more efficient in the transmission of power. The usual waveform of an AC power circuit was a sine wave. This is because the sine wave resulted in the most efficient transmission of energy. Another great advantage of AC current was that it could be stepped up or down to a different voltage, using a transformer. However, AC current did also have some disadvantages. One disadvantage was the safety of the public and operators handling the AC wires. Since AC current was high in voltage, it could easily electrocute a person and kill him instantly. Therefore, installation and repair of the AC wires were also a hazard. Moreover, AC wires needed more insulation than DC wires, and therefore cost more. However, AC's ability to go long distances was a greater marginal benefit. During the “War of Electrification”, Tesla developed the first AC electric generator and teamed up with Westinghouse to eventually rule the Electrical industry with AC power rather that Edison's DC power which had been prevalent before.

References:
1) AC and Tesla - http://www.pbs.org/tesla/ins/ins_acdc.html
2) AC - http://www.ibiblio.org/obp/electricCircuits/AC/AC_1.html

Kirchhoff's Laws:
Kirchhoff has two laws; one is Kirchhoff's Voltage Law, and the other is Kirchhoff's Current Law. Together both laws are very useful tools in analyzing electrical circuits and in understanding the transfer of energy through an electrical circuit. Kirchhoff's Voltage Law was discovered in 1847 by Gustav R. Kirchhoff. Kirchhoff's Voltage Law states that the “algebraic sum of all voltages in a loop must equal zero.” This law works for any type of circuit configuration, not just simple series. Moreover, this law can be used to determine an unknown voltage in a complex circuit. However, all other voltages around the particular loop have to be known. Kirchhoff's current law states that the “algebraic sum of all currents entering and exiting a node must equal zero.” This means: I(exiting)=I(entering) and I(entering)+[-I(exiting)]=0.

References:
1) Kirchhoff's Law - http://www.allaboutcircuits.com/vol_1/chpt_6/2.html

Direct Curent:
Direct current (DC) is a current source which goes in one direction. It was mainly used as the primary electricity source during the later part of the 19th century. DC current was preferred by Thomas Edison also known as “The wizard of Menlo park”. DC current was used by Edison, because he believed it to be safer than Alternating current (AC). Although DC current was safer, it had some limitations of the distance it could travel which eventually made it lose the battle between its counterpart, AC current. Today, we use both of the current sources.

References:
1) Direct Current - http://www.pbs.org/wgbh/amex/edison/sfeature/acdc.html

Parallel Circuits:
Circuits are divided into two categories: series and parallel. Series circuits allow for the passage of current in only one direction where as the parallel circuit allows the current to pass through multiple directions. As a result, if there is a break with in the circuit, the current flow is not disrupted in a parallel circuit. Consequently, parallel circuits are preferred for various projects.
References:
1) Parallel Circuits - http://www.allaboutcircuits.com/vol_1/chpt_5/1.html

Voltage:
Voltage is named after Alessandro Volta, an Italian physicist, who discovered the first modern chemical battery in 1881. The discovery of the electric battery has revolutionized people’s lives forever, as we are able to use portable electronics almost anywhere today due to the invention of the battery. Voltage is ultimately the power source of a circuit. The voltage is represented in ohm's law as E, and is commonly referred to as potential difference. Voltage is directly related to both current and resistance.
References:
1) Voltage - http://jersey.uoregon.edu/vlab/Voltage/

Polyphase Alternating Current:
Polyphase alternating current is a way for a strong voltage to be transmitted in multiple low voltages to reduce danger and produce a high efficiency. This form of AC helps because there are lesser voltages that combine together to have the strength of the total higher voltage.
References:
1) http://www.allaboutcircuits.com/vol_2/chpt_10/2.html


Induction:
Electromagnetic induction is a very important concept that makes many things possible from generators and motors to the transmission of electricity over great distances. Electromagnetic induction is caused when a wire is put into a changing magnetic field. This change in magnetic field causes a current to flow through the wire. Also this causes a magnetic force on the wire that resists this motion. By placing two coils with a different coil amount next to each other and running AC current through the coils one can either step up or step down voltage. This becomes useful for transmitting electricity over high distances as large AC voltages are easier to send then smaller ones. By moving a magnet past the coils once can generate electricity. Generators use exactly this same concept except in a rotary fashion.

References:
1) http://library.thinkquest.org/13526/c3c.htm

Electromagnetism:
Electromagnetism is how electricity and magnetism are related and how they interact. It wasn’t until the 19th century that people started making connections about the interactions of the two. Electric fields have the ability to produce magnetic ones and vice versa. Faraday used this in early experiments in generating electricity.

References:
1) http://www.britannica.com/eb/article-9106021

Electric Power:
Electric power is the amount of work done by an electric circuit. The resistance in a circuit affects how much work this is. Devices such as heaters and light bulbs use large “resistors” (usually a coiled conductor) use this power to generate heat and light. Power is measured in the unit watts, represented by W.

References:
1) http://en.wikipedia.org/wiki/Electric_power