Engineering Module - Semester I (Electronic & Electrical Engineering) PDF

INTERNATIONAL & ACCESS FOUNDATION PROGRAMMES Engineering Module - Semester I Electronic & Electrical Engineering Part 2 Introduction to Electricity Dr Nevan Bermingham What is Electricity? The controlled flow of electrons in an electrica...

INTERNATIONAL & ACCESS FOUNDATION PROGRAMMES Engineering Module - Semester I Electronic & Electrical Engineering Part 2 Introduction to Electricity Dr Nevan Bermingham What is Electricity? The controlled flow of electrons in an electrical circuit. A circuit must always be a complete loop. Electricity is considered POSITIVE charge or NEGATIVE charge Lightening is a natural example of electricity 2 Building Blocks Electricity is generated from the motion of tiny charged atomic particles called electrons. Atoms are made up of  Nucleus  Protons (+)  Neutrons  Electrons (-) 3 ATOMS Electrons have a NEGATIVE charge Protons have a POSITIVE charge Neutrons have a no charge 4 ATOMS – The Bohr Model 5 Electrons – Is the Bohr Model Right? 6 Conductors Let electricity flow readily Few electrons in outer shell 1 or 2 electrons Free electrons in outer shell Copper, gold, silver Platinum, aluminum, most other metals 7 Insulators Do not let electrons flow Outer shell full or close to full 6-7-8 electrons Full outer electron shell Glass, plastic Porcelain, wood Rubber 8 Insulators 9 Insulators 10 Electricity Electricity Charges – Movement of Electrons Positive charges attract negative charges Negative charges attract positive charges In other words – opposite charges attract Same charges repel each others So, electrify is the 13 Circuits Current flows from Positive to Negative 14 Circuits A Circuit or loop is necessary for current to flow Current takes the path of least resistance So does a bird on an electric wire get electrocuted? 15 How is Electricity Produced? Friction: “static electricity” from rubbing (walking across a carpet), resulting from the imbalance between positive and negative charges within a material Pressure: piezoelectricity from squeezing crystals together (quartz watch) Heat: voltage produced at junction of dissimilar metals (thermocouple) Light: voltage produced from light striking photocell (solar power) Chemical: voltage produced from chemical reaction (wet or dry cell battery) Magnetism: voltage produced using electromotive induction (AC or DC generator). Piezoelectricity – the heart of the modern computer See You Tube Video Early History 1752 – Lightning Rod 1879 – Light Bulb Ben Franklin Thomas Edison 1800 – Electric Battery 1888 – AC Power Count Alessandro Volta Nikola Tesla 1805 – Refrigerator 1910 – Flashlight Oliver Evans Conrad Hubert 1876 – Telephone 1920 – Basic Terminology Electromotive Force (V) Force which causes electrons to move from one location to another Known as emf, potential difference, or voltage Unit is volt (V) Source:  Generator  Battery Like pump that moves water through “pressure” Basic Terminology Current (I) Flow of electric charges - electrons (or holes) - through a conductor or circuit per increment of time Unit is ampere (number of charged particles passing a point each second) 1 amp = 1 coulomb/sec = 6x1018 electrons/sec Like rate of flow of water through a pipe While electrons flow from negative to positive, CONVENTIONAL CURRENT says that current flows from positive to negative. Conventional Current In 1752, prior to electricity being identified with the electron, Ben Franklin chose a convention regarding the direction of current flow. Franklin assumed that positive charge carriers flowed from positive to negative terminals. We now know this is incorrect. The flow of electrons is termed electron current. Electrons flow from the negative terminal to the positive. Conventional current or simply current, behaves as if positive charge carriers cause current flow. However, we use conventional flow as the norm in engineering. Basic Terminology Resistance (R) An electrical circuit’s opposition to the flow of current through it Measured in ohms (W) Conductor All materials will conduct electricity, but at varying resistances Good conductors have little resistance (ie: silver, copper, aluminum, iron) Basic Terminology Insulator Substances which offer high resistance to current flow (ie: wood, rubber, plastics) Circuits made of wires covered with insulator Power (P) Rate at which work is performed Measured in watts (W) Power = Voltage x Current Or P = V.I Watts Power Generation Chemical Cells Electrodes Electrolyte Conductor Wet/Dry Batteries Magnetism Batteries The basic primary wet cell  The metals in a cell are called the electrodes, and the chemical solution is called the electrolyte.  The electrolyte reacts oppositely with the two different electrodes  It causes one electrode to lose electrons and develop a positive charge; and it causes one other electrode to build a surplus of electrons and develop a negative charge.  The difference in potential between the two electrode charges is the cell voltage. Cells Positive electrode (Copper Cu) Negative electrode (Zinc Zn) Electrolyte (Sulfuric Acid & Water H2SO4) Separator (carries negative  The Electrolyte & Electrolysis  When charging first started, electrolysis broke down each water molecule (H2O) into two hydrogen ions (H+) and one oxygen ion (O-2).  The positive hydrogen ions attracted negative sulfate ions (SO4-2) from Licensed under CC BY-SA 3.0 via Commons - https://commons.wikimedia.org/wiki/File:Galvanic_cell_with_no_cation_flow.png#/media/ File:Galvanic_cell_with_no_cation_flow.png each electrode.  These combinations produce H2SO4, which is sulfuric acid. Dry Cell Batteries Lithium Ion Batteries Lithium Ion Batteries Electron Orbits (Clouds) How Electron Move Any Questions?