1 Electronics Technology Fundamentals Chapter 1 Principles of Electricity Lindem 14 jan.07

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

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 Versus Alternating Current 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 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 Insert Figure 1.13 Ohms lov U = R · I Denne læreboka skiller ikke mellom U og V

Resistance and Conductance – P2 Conductance ( Ledningsevne ) – 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) where G= conductance R = resistance

Resistance and Conductance – P3 Examples 1. Calculate the conductance of a 10 K  resistor. 2. Calculate the resistance of a circuit that has a conductance of 25 mS.

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 where  = resistivity (greek letter, rho) ℓ = length A= cross-sectional area

Conductors, Insulators and Semiconductors – P5 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

19 End 1. Fargekode for motstander