Principles of Electricity

Electronic ConceptsHussam Al-HertaniPrinciples of ElectricityThe Oldest Analogy in ElectronicsElectronic Concepts 2010 - Hussam Al-Hertani2

Elements, Atoms and ChargeElectronic Concepts 2010 - Hussam Al-Hertani3MatterMatter anything that has weight and occupies spaceElement substance that cannot be broken down into a combination simpler substances

Atomic StructureAtom smallest particle of matter that retains the physical characteristics of an elementBohr ModelSimplest model of an atomCentral core (nucleus) contains protons and neutronsElectrons revolve around nucleus

Elements, Atoms and ChargeElectronic Concepts 2010 - Hussam Al-Hertani4

The Starting Point: Elements, Atoms and ChargeElectronic Concepts 2010 - Hussam Al-Hertani5Atomic Structure (Continued)Atomic Number of an Atom number of protonsAtoms contain an equal number of protons and electronsElectrons travel in orbital paths (shells)Valence ShellOutermost shellCannot hold more than eight electronsComplete shell contains eight electronsThe Starting Point: Elements, Atoms and ChargeElectronic Concepts 2010 - Hussam Al-Hertani6

The Starting Point: Elements, Atoms and ChargeElectronic Concepts 2010 - Hussam Al-Hertani7ChargeForce that causes two particles to be attracted to, or repelled from, each otherTwo types positive and negativeAtom proton (positive), electron (negative), neutron (electrically neutral)

Elements, Atoms and ChargeElectronic Concepts 2010 - Hussam Al-Hertani8Attraction and Repulsion - Like charges repel each other and opposite charges attract each other

IonsOutside force can cause an electron to leave its orbit -atom is referred to as a positive ionOutside force can cause an atom to gain an electron -atom is referred to as a negative ion

Free ElectronsAn electron that is not bound to any particular atomCan neutralize a positive ion

Elements, Atoms and ChargeElectronic Concepts 2010 - Hussam Al-Hertani9

CurrentElectronic Concepts 2010 - Hussam Al-Hertani10Current the directed flow of charge through a conductorThermal energy (heat) is sufficient to free electrons in copperFree electron motion is random unless outside force is applied

CurrentElectronic Concepts 2010 - Hussam Al-Hertani11Represented by the letter I (for intensity)Measured in charge per unit timewhere I = the intensity of the currentQ = the amount of charge t = the time (in seconds) required for the charge (Q) to pass

11CurrentElectronic Concepts 2010 - Hussam Al-Hertani12Coulomb (C) represents the total charge of approximately 6.25 x 1018 electronsUnit of Current 1 Ampere (A) = 1 coulomb/second (C/s)Example:3 coulombs of charge pass a point in a wire every two seconds. Circuit current is found as

CurrentElectronic Concepts 2010 - Hussam Al-Hertani13Electron Flow Versus Conventional Current

CurrentElectronic Concepts 2010 - Hussam Al-Hertani14Direct Current Versus Alternating CurrentDirect Current (dc) unidirectional, always flows in one directionAlternating Current (ac) bidirectional, periodically changes direction

CurrentElectronic Concepts 2010 - Hussam Al-Hertani15

VoltageElectronic Concepts 2010 - Hussam Al-Hertani16Voltage a difference of potential that generates a directed flow of charge (current) through a circuit

VoltageElectronic Concepts 2010 - Hussam Al-Hertani17Often referred to as electromotive force (EMF)

Unit of Voltage volt (V) = 1 joule/coulomb

Volt the difference of potential that uses one joule of energy to move one coulomb of charge.

1 V = 1 J/C

Resistance and ConductanceElectronic Concepts 2010 - Hussam Al-Hertani18Resistance opposition to currentUnit of Resistance ohm ( - Greek letter omega)Ohm the amount of resistance that limits current to one ampere when one volt is applied

Resistance and ConductanceElectronic Concepts 2010 - Hussam Al-Hertani19Conductance a measure of the ease which current will pass through a component

Unit of Conductance siemens (S)Old Unit of Conductance mhos (upside down omega symbol)

whereG= conductanceR = resistanceConductors, Insulators and SemiconductorsElectronic Concepts 2010 - Hussam Al-Hertani20ExamplesCalculate the conductance of a 10 K resistor.

Calculate the resistance of a circuit that has a conductance of 25 mS.

Conductors, Insulators and SemiconductorsElectronic Concepts 2010 - Hussam Al-Hertani21Conductors materials that provide little opposition to the flow of charge (current)Example: copperFew valence shell electrons, one valence shell electron per atom makes the best conductor

Insulators materials that normally block currentExample: rubberComplete valence shell (8 electrons)Conductors, Insulators and Semiconductors Electronic Concepts 2010 - Hussam Al-Hertani22Semiconductors materials that are neither good conductors nor good insulatorsExamples: - graphite (used to make resistors) - silicon - germaniumHalf-complete valence shells (four valence electrons)

Conductors, Insulators and Semiconductors Electronic Concepts 2010 - Hussam Al-Hertani23Other Factors that Affect ResistanceResistivity the resistance of a specified volume of an element or compound CM-/ft Circular-mil ohms per footMil is one thousandth of an inch (0.001 in)The circuilar mil (CM) is the area of a 1mil diameter circle-cm Ohm-centimetersLengthCross-Sectional Area

Conductors, Insulators and Semiconductors Electronic Concepts 2010 - Hussam Al-Hertani24Calculating the Resistance of a Conductor

Resistivity table provided on page 39 of text

where= resistivity (greek letter, rho) = lengthA= cross-sectional areaConductors, Insulators and Semiconductors Electronic Concepts 2010 - Hussam Al-Hertani25

Example

Calculate the resistance of a 25 cm length of copper that has a cross-sectional area of 0.04 cm2.Conductors, Insulators and SemiconductorsElectronic Concepts 2010 - Hussam Al-Hertani26The Effects of Temperature on Resistance

Positive Temperature CoefficientResistance increases as temperature increases and vice versaExample: most conductors

Negative Temperature CoefficientResistance decreases as temperature increases and vice versaExample: most semiconductors and insulatorsIn Class Problem SolvingElectronic Concepts 2010 - Hussam Al-Hertani27P41 Q. 3, 7, 13, 15, 17