Presentation on theme: "1 Electronics Technology Fundamentals Chapter 1 Principles of Electricity Lindem 11. jan 09."— Presentation transcript:
1 Electronics Technology Fundamentals Chapter 1 Principles of Electricity Lindem 11. jan 09
2 1.1 The Starting Point Atomic Structure Atom – smallest particle of matter that retains the physical characteristics of an element Bohr Model Simplest model of an atom Central core (nucleus) – contains protons and neutrons Electrons revolve around nucleus
3 1.1 The Starting Point: Elements, Atoms and Charge – P3 Atomic Structure (Continued) Atomic Number of an Atom – number of protons Atoms contain an equal number of protons and electrons Electrons travel in orbital paths (shells) Valence Shell Outermost shell Cannot hold more than eight electrons Complete shell contains eight electrons
4 1.1 The Starting Point: Elements, Atoms and Charge – P6 Attraction and Repulsion - Like charges repel each other and opposite charges attract each other Ions Outside force can cause an electron to leave its orbit -atom is referred to as a positive ion Outside force can cause an atom to gain an electron -atom is referred to as a negative ion Free Electrons An electron that is not bound to any particular atom Can neutralize a positive ion
5 1.1 The Starting Point: Elements, Atoms and Charge – P7 Det enslige elektronet i ytterste ”skall” er svakt bunnet til kjernen. Ved ”normal” temperatur har vi ca 1 fritt elektron pr. atom - ca elektroner / cm3 Figuren viser et kopperatom.
6 1.2 Current – P1 Elektrisk strøm Current – the directed flow of charge through a conductor Thermal energy (heat) is sufficient to free electrons in copper Free electron motion is random unless outside force is applied
7 1.2 Current – P2 Elektrisk strøm Represented by the letter I (for intensity) Measured in charge per unit time where I = the intensity of the current (Ampere) Q = the amount of charge ( coulomb ) t = the time (in seconds) required for the charge (Q) to pass Coulomb (C) – represents the total charge of approximately 6.25 x electrons Unit of Current – Ampere (A) = 1 coulomb/second 3 coulombs of charge pass a point in a wire every two seconds. Calculate current.
8 1.2 Current – P4 Electron Flow Versus Conventional Current Insert Figure 1.10
9 1.2 Current – P5 Direct Current - DC Versus Alternating Current - AC Direct Current (dc) – unidirectional Alternating Current (ac) - bidirectional
Voltage – P1 Voltage – a “difference of potential” that generates the directed flow of charge (current) through a circuit Often 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.
Resistance and Conductance – P1 - Motstand og ledningsevne Resistance – opposition to current Unit of Resistance – ohm ( - Greek letter omega) Ohm – the amount of resistance the limits current to one ampere when one volt is applied Ohms lov Tradisjonelt bruker vi ofte U som betegnelse for spenning. Boka har imidlertid konsekvent valgt å benytte V ( U = R · I )
12 Conductance ( Ledningsevne ) – a measure of the ease which current will pass through a component Unit of Conductance – siemens (S) where G= conductance R = resistance Examples 1. Calculate the conductance of a 10 K resistor. 2. Calculate the resistance of a circuit that has a conductance of 25 mS. 1.4 Resistance and Conductance – P2 - Motstand og ledningsevne
Conductors, Insulators and Semiconductors – P1 Conductors – materials that provide little opposition to the flow of charge (current) Example: copper Few valence shell electrons, one valence shell electron per atom makes the best conductor Insulators – materials that normally block current Example: rubber Complete valence shell
Conductors, Insulators and Semiconductors – P2 Semiconductors – materials that are neither good conductors nor good insulators Example: graphite (used to make resistors) Half-complete valence shells (four valence electrons) Silisium (Si)Germanium (Ge) 4 valenselektroner
Conductors, Insulators and Semiconductors – P3 Other Factors that Affect Resistance Resistivity – the resistance of a specified volume of an element or compound CM- /ft – Circular-mil ohms per foot -cm – Ohm-centimeters Length Cross-Sectional Area = resistivity (greek letter, rho) ℓ = length A= cross-sectional area Example Calculate the resistance of a 25 cm length of copper that has a cross- sectional area of 0.04 cm 2.
Conductors, Insulators and Semiconductors – P6 The Effects of Temperature on Resistance Positive Temperature Coefficient Resistance increases as temperature increases and vice versa Example: most conductors Negative Temperature Coefficient Resistance decreases as temperature increases and vice versa Example: most semiconductors and insulators End 1.