DC Theory Test 1

Factors Effecting Conductor Resistance

(1) Type of material (2) Length Resistance is directly proportional to length (3) Cross - Sectional area. Resistance is inversely proportional to cross sectional area (CSA) (4) Temperature - Most pure metals have a (+) temperature coefficient (As temp goes up resistance goes up) - A(+) temperature coefficient results in an increase of resistance as temperature increases. - A(-) temperature coefficient results in a decrease of resistance as temperature increases.

Effects of Electricity

1) Magnetism ( Mohrs & Transformer) 2) Chemical reaction ( Electroplating) 3) Pressure ( Quartz Crystals) 4) Heat 5) Light

Methods of producing electricity

1) Magnetism - Generators and Alternators 2) Chemical Reaction - Battery 3) Pressure - Piezo Electric effect Involves striking, bending, and / or twisting certain types of crystals 4) Heat - Seebeck effect and Thermcouples 5) Fricition - Static Electricity 6) Light - Photovoltaic

Uses of Static Electricity

1) Paint Application 2) Removing dust particles from air 3) Recovering valuable products from gases 4) separating materials

Photon

A mass less particle of pure energy. They can be produced when electrons move from one energy level to another

Centripetal Force

According to Newton's 1st Law of Motion, a body continues in a state of rest or uniform motion in a straight line unless acted upon by an external force

Characteristics of good conductors:

Allows for easy flow of electrons Inexpensive Easily extruded into wire Corrosion Resistant Easily obtainable Malleable, flexible

Free Electrons

An Electron that is not in orbit or attached to an atom

Neutrons

An atom may or may not contain the same number of neutrons as protons in its nucleus

Matter

Any substance that has weight & occupies space. Made up of a combination of atoms Can exist in any of three states; solid, liquid, or gas

Copper Conductors

Are better conductors Have less resistance per circular mil foot than aluminum conductors Smaller wires will carry more current safely Resist Oxidation better than aluminum Allow for better quality connections & terminations due to the rate of expansion & contraction of metal during temperature fluctuation.

Valence Electrons

Are located in the outer orbit of an atom

Insulators

Are materials that do not provide an easy path for the flow of electrons. They are generally made from materials containing seven or eight valence electrons

Conductors

Are materials that provide an easy path for electron flow. They are made from materials that contain from one to three valence electrons They are unstable and can easily be forced out of orbit Silver, Copper, and Gold all have 1 Valence Electon

Stranded wires

Are more flexible than solid wires Used for larger conductors Easier to pull through conduit Do not transmit vibration Used for connections to motors, and other mechanical equipment that produces motion and/ or vibration Make better connections in a "set screw type" termination

Aluminum Conductors

Are much lighter than copper Are less expensive than copper Require use of anti-oxidation paste at terminals and connections

Semiconductors

Contain four valence electrons. They are used in the construction of all solid-state devices, such as diodes, transistors, and integrated circuits. Semi Conductor materials do not possess characteristics of good insulators or conductors. They are primarily used in electronic components. Silicon and Germanium are examples of semi conductors. And are the only substances that's resistance decreases as its temp increases

Characteristics of good insulators

Does not conduct/ has high resistance Long Life Resistance to high temperature ( lettering on jacket) Resistance to moisture Mechanical flexibility Resistant to ionization - will not break down under use No material is good at all of the above

Valence Electron

Electrons contained in the Valence Shell Elements with the same # of Valence Electrons tend to have similar properties The # of Valence electrons determine chemical and electrical properties

Solid Wires

Hold their shape Used in smaller stationary installations are less expensive

Electricity

Is the flow of electrons

Electrostatic Induction

Is the process by which a neighboring object acquires a charge. If there is no conductive path between charged objects, thousands of Volts can remain between them. Static charges will not accumulate between objects that are bonded together & grounded

Molecule

Is the smallest part of a compound

1st Electron Orbit

K max of 2 electrons

2nd Electron Orbit

L max of 8 electrons

3rd Electron Orbit

M max of 18 electrons

6 basic methods for producing electricity

Magnetism, Chemical Action, Light, Heat, Pressure, and Fricition

5 basic effects that can be caused by electricity

Magnetism, Chemical Reactions, Light, Heat, and Pressure

4th Electron Orbit

N max of 32 electrons

Electron Flow

Occurs when an electron from one atom knocks electrons of another atom out of orbit

Electrons

Orbit the outside of the Nucleus

Valence Shell

Outer most electron orbit and can not hold more than 8 electrons

3 Principal parts of an atom

Proton (+) , Electron(-) , Neutron (0)

The Nucleus

Protons & Neutrons are located in the nucleus of the atom while the electron orbit around the nucleus

Calculating the resistance of a conductor

R= K L / CSA R = Resistance K = Resistivity (ohms per circular mil-foot) L = Length (feet) CSA = Cross Sectional Area (Circular Mils) If diameter is given it must be converted to cross sectional area in circular mils. To convert from diameter to CSA move the decimal point 3 places to the right then square that number. Ex. .050" = 50square = 2500

In Ohm's Law The letter E or V

Represents Voltage which is referred to as electric pressure, potential difference, or electromotive force

In Ohm's Law The Letter W or P

Represents Watt which is a measurement in an electrical circuit

In Ohm's Law The letter I

Represents intensity of current flow

Temperature formula

Resistance = R@20 [ 1 + temp coefficient (degree rise)]

Atom

Smallest particle of an element

3 things needed for electricity

Source, Closed circuit path, Resistance

Coulombs Law of Electrostatic Charge

States that the force of electrostatic attraction or repulsion is directly proportional to the square of the distance between them. Direct proportional relationship (speed would be the same force) Double the voltage= Double the current

Common Insulating materials

Synthetic Rubber Thermoplastic Paper Asbestos Cotton Yarn Enamel Cross Linked Synthetic polymers

Protons

The number of protons in the nucleus determines what kind of element the atom is

Static Electricity

The result of an imbalance of the "fluid" (electrons) between objects Static is not moving or sitting still

Lightning is an example of

a natural static charge

Electric Measurements

are generally expressed in Engineering Notations

An object can be negatively charged

by adding electrons to it

An object can be positively charged

by removing electrons from it

A open circuit

has infinite resistance

A short circuit

has little to no resistance

Engineering Notations differs from scientific notations

in that it uses steps of 1000 instead of steps of 10

An Ampere

is 1 Coulomb per second

An electroscope

is a device used to determine the polarity of a object

Coulomb

is a measure of charge

An Ohm

is a measurement of (R) Resistance in an electrical circuit

Temperature Coefficient

is the proportion that R changes per degree rise in temperature. For every degree increase or decrease, there will be a proportional change is resistance based on the type of material.

Static

means not moving

Static charges accumulate

on insulator materials

The Law of Charges

opposite charges attract, like charges repel

Conductors

sizes are measured in American Wire Gage and/or circular mills. One circular mill is the area of a conductor that is .001" in diameter. One circular mill foot is a conductor with a cross sectional area of our circular mill and a length of one foot. Conductors are typically measured with either a micrometer or a wire gage. Wire strippers can also be used to determine the gauge or size of a wire.

Before current can flow

there must be a complete circuit