Electronic Concepts Hussam Al-Hertani Principles of Electricity

The Oldest Analogy in Electronics Electronic Concepts Hussam Al-Hertani 2

Elements, Atoms and Charge Electronic Concepts Hussam Al-Hertani 3 Matter Matter – anything that has weight and occupies space Element – substance that cannot be broken down into a combination simpler substances 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

Elements, Atoms and Charge Electronic Concepts Hussam Al-Hertani 4

The Starting Point: Elements, Atoms and Charge Electronic Concepts Hussam Al-Hertani 5 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

The Starting Point: Elements, Atoms and Charge Electronic Concepts Hussam Al-Hertani 6

The Starting Point: Elements, Atoms and Charge Electronic Concepts Hussam Al-Hertani 7 Charge Force that causes two particles to be attracted to, or repelled from, each other Two types – positive and negative Atom – proton (positive), electron (negative), neutron (electrically neutral)

Elements, Atoms and Charge Electronic Concepts Hussam Al-Hertani 8 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

Elements, Atoms and Charge Electronic Concepts Hussam Al-Hertani 9

Current Electronic Concepts Hussam Al-Hertani 10 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

Current Electronic Concepts Hussam Al-Hertani 11 Represented by the letter I (for intensity) Measured in charge per unit time where I = the intensity of the current Q = the amount of charge t = the time (in seconds) required for the charge (Q) to pass

Current Electronic Concepts Hussam Al-Hertani 12 Coulomb (C) – represents the total charge of approximately 6.25 x electrons Unit 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

Current Electronic Concepts Hussam Al-Hertani 13 Electron Flow Versus Conventional Current

Current Electronic Concepts Hussam Al-Hertani 14 Direct Current Versus Alternating Current Direct Current (dc) – unidirectional, always flows in one direction Alternating Current (ac) – bidirectional, periodically changes direction

Current Electronic Concepts Hussam Al-Hertani 15

Voltage Electronic Concepts Hussam Al-Hertani 16 Voltage – a “difference of potential” that generates a directed flow of charge (current) through a circuit

Voltage Electronic Concepts Hussam Al-Hertani 17 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. 1 V = 1 J/C

Resistance and Conductance Electronic Concepts Hussam Al-Hertani 18 Resistance – opposition to current Unit of Resistance – ohm (  - Greek letter omega) Ohm – the amount of resistance that limits current to one ampere when one volt is applied

Resistance and Conductance Electronic Concepts Hussam Al-Hertani 19 Conductance – 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

Conductors, Insulators and Semiconductors Electronic Concepts Hussam Al-Hertani 20 Examples – Calculate the conductance of a 10 K  resistor. – Calculate the resistance of a circuit that has a conductance of 25 mS.

Conductors, Insulators and Semiconductors Electronic Concepts Hussam Al-Hertani 21 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 (8 electrons)

Conductors, Insulators and Semiconductors Electronic Concepts Hussam Al-Hertani 22 Semiconductors – materials that are neither good conductors nor good insulators Examples: - graphite (used to make resistors) - silicon - germanium Half-complete valence shells (four valence electrons)

Conductors, Insulators and Semiconductors Electronic Concepts Hussam Al-Hertani 23 Other Factors that Affect Resistance Resistivity – the resistance of a specified volume of an element or compound CM-  /ft – Circular-mil ohms per foot Mil is one thousandth of an inch (0.001 in) The circuilar mil (CM) is the area of a 1mil diameter circle  -cm – Ohm-centimeters Length Cross-Sectional Area

Conductors, Insulators and Semiconductors Electronic Concepts Hussam Al-Hertani 24 Calculating the Resistance of a Conductor Resistivity table provided on page 39 of text where  = resistivity (greek letter, rho) ℓ = length A= cross-sectional area

Conductors, Insulators and Semiconductors Electronic Concepts Hussam Al-Hertani 25 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 Electronic Concepts Hussam Al-Hertani 26 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

In Class Problem Solving Electronic Concepts Hussam Al-Hertani 27 P41 Q. 3, 7, 13, 15, 17