Basic Electricity
Restivity values of some conductors in their proper order to each other
Silver - 9.8Ω Copper - 10.4Ω Gold - 14.0Ω Aluminium - 19.3Ω Tungsten - 33.8Ω Nickel - 52.0Ω Iron - 58.0Ω Steel - 100.0Ω
Factors effecting resistance
Temperature of a conductor - Usually the resistance of a conductor increases with an increase in temperature. Type of conductor material - Ability of a conductor to conduct current flow. *Resistance for any given conductor is based on a given diameter and length. The constant values for any conductor is based on one thousandths of an inch (0.001") and 1ft in length. Length of the conductor of wire - The longer the length of a given size wire, the greater the electrical resistance becomes. Cross sectional area of the conductor or wire - Measured in circular mils. One circular mil has the equivalent area of one circle, if that circle has a diameter of 0.001" or one mil. The resistance of a conductor decreases as the cross sectional area increases. When the diameter of a conductor is given in mils, its cross sectional area in mils is equal to the electrical diameter squared.
Coulomb
The accumlated charge of 6.28 billion, billion free electrons. Using powers of 10, this would equal to 6.28 x 10^18. When this quantity of free elecyrons pass through a given point in an electrical circuit, one ampere of a current is said to be flowing.
Elements
The basic material that makes up all matter. A natural element is one that is found in nature. Substances composed of only one type of atom.
Electrons
The particle in an atom carrying a negative electrical charge.
Neutrons
The particle in an atom carrying a neutral of no electrical charge.
Electrical resistance
The property of a conductor which tends to hold back or resist the flow of an electrical current. The unit used to measure electrical resistance is called the ohm, (Ω). In mathematical formulas, the capital letter "R" refers to resistance. Example: (R= 20Ω)
Atom
The smallest particle of an element that can be reduced to and still keep the properties of the element.
Molecule
The smallest particle of matter that can exist and still retain its identity.
Compound
A chemical combination of two or more elements.
Matter
Anything that occupies space and has mass; solids, liquids and gases.
Total resistance of a conductor
Can be found by using the following formula: Rt = KL/S (Rt = KL ÷ S) Rt = total resistance K = resistivity constant L = length of wire or conductor measured in ft S = cross sectional area of wire measured in circular mils
Ohm's law
Compares the relationship between voltage, current flow and resistance in electrical circuits. This law applies to all direct current circuits and in a modified form to alternating current circuits. EMF is messured in volts and expressed by the letter "E". Current flow is measured and expressed by the letter "I". Resistance is measured in ohms and expressed by the letter "R". One volt is one EMF potential required to cause one amp of current flow to move through one resistance of on ohm per second.
Electrical current
Defined as the flow of electrons through a conductor because of a difference in electrical pressure, (potential) between the ends of a conductor when connected to a power supply.
E = I x R
E = Volts I = Amps R = Resistance
Current flow
Electrons in morion make up an electrical current. No matter how many electrons are moving, when it's in one direction only, it's called direct current.
Kilovolt
Kilo means 1,000 and when used with volts, it's expressed as kilovolt meaning 1,000 volts (1,000 volts = 1kV or 1/1,000 kV) (Written as 0.001kV)
Insulator
Material which would not allow a large number of free electrons to flow through them when connected to a power supply.
Conductors
Materials which would allow large numbers of free electrons to flow through them when connected to a power supply.
Millivolt
Milli means one-thousandth. 1 millivolt = one-thousandth (1/1,000) of a volt. (0.001 mV)
Electricity
Often described as being either static or dynamic. The difference is that static is when electrons are at rest while dynamic, the electrons are in motion.
Mega (M)
One million (1,000,000)
Kilo (k)
One thousand (1,000)
Milli (m)
One-thousandth (1/1,000)
P = I x E
P = Power I = Amps E = Volts
Intensity
Represents amperage in the capital letter "I". One amp is the rate of flow of one coulomb per second. Current is assumed to flow at the speed of light. 186,000 mi/sec
Electrical power
The unit used to measure power in direct current (dc). Electrical circuits is the watt. One horsepower (hp) is the mechanical power required to raise 550lbs a distance of 1ft in one second or 33,000lbs a distance of 1ft in one minute. Electrical power equivalent to one hp = 746 watts. In electrical theory, 1 watt is the power expended when one volt of electrical potential causes one amp of current to flow through a resistance of one ohm. W = E x I W = Watts E = Volts I = Amps
Ammeter
Used fo measure amperage. It's connected to a circuit in series with the electrical load.
Ohmmeter
Used to measure resistance. It's connected across the resistance to be measured only after the resistance has been disconnected from its power supply. It corporates its own power supply and is primarily used to check a circuits continuity.
Voltmaster
Used to measure voltage. It's connected to a circuit in parallel with the electrical load. It must be connected across a potential difference to indicate a voltage reading.
Examples of total resitance of a conductor used in problems
What is the total resistance of copper wire having a length of 300ft and a diameter of 0.005"? Restivity of copper wire is 10.4Ω per circular mil foot. 10.4 x 300ft / 25 circular mils = 124.8Ω. What is the total resistance of copper wire having a length of 300ft and a diameter of 0.010"? 10.4 x 300 / 100 circular mils = 31.2Ω. Diameter - 0.010" = 10 mils. S = 10 squared = 10 circular mils.
Free electrons
When one electron moves from one atom to another.
Examples of cross sectional area of the conductor or wire used in a problem
Wire diameter = 0.001" = 1 mil. cross sectional area = 1 mil squared. 1^2 = 1 x 1 = 1 circular mils. Wire diameter = 0.002" = 2 mil. cross sectional area = 2 mil squared. 2^2 = 2 x 2 = 4 circular mils. Wire diameter = 0.005" = 5 mil. cross sectional area = 5 mil squared. 5^2 = 5 x 5 = 25 circular mils.
