Transcript Electricity
ELECTRICITY STATIC ELECTRICITY FRANKLIN’S EXPERIMENT OPPOSITE CHARGES ATTRACT, LIKE CHARGES REPEL BATTERIES VOLTS, WATTS AND OHMS VOLTAGE IS THE “FORCE” THAT DRIVES CURRENT THROUGH A CONDUCTOR UNIT IS THE VOLT CURRENT IS THE FLOW OF CHARGE, UNIT IS THE AMPERE OHMS IS THE RESISTANCE TO THAT FLOW Voltage = resistance x current; V= RI This is known as Ohm’s Law ELECTRICAL POWER WATT IS A MEASURE OF THE POWER USED WATT=VOLT-AMPERES W=VI = RI2 Power is lost to heat as electrons encounter resistance to their flow through the conductor. A kettle at 120V causes 12.5 Amps to flow through the heating element that has a resistance of 9.6 Ohms. Power consumed is 120 x 12.5 = 1500 Watts. If it takes 6 minutes (0.1 hr) to boil the water, and the price of electricity is 6 $.06/kW-hr, that will cost you 0.15kWhr=0.9 cents TRANSMISSION OF POWER Power lines lose power due to resistance in the wires. W=RI2. The resistance is related to the size of the wire and what it is made of. But V=RI, so W=VI. Thus, if we can increase the voltage, we can use less current to send the same power, and reduce resistance losses. ELECTRICAL CIRCUIT ELEMENTS RESISTANCE - OHMS CAPACITANCE - FARADS INDUCTION ELECTRICAL CIRCUITS CURRENT R I C AC DC DIRECT CURRENT (DC): THE CURRENT FLOWS IN ONE DIRECTION ALTERNATING CURRENT (AC) THE CURRENT OSCILATES BACK AND FORTH + - TIME MAGNETISM PERMANENT MAGNETS MAGNETIC FIELD LINES N THE EARTH IS A MAGNET N S S ELECTROMAGNETIC WAVES EM WAVES ARE WHAT LIGHT, RADIO, THERMAL, X-RAY AND GAMMA RAYS ARE MADE OF. They need no medium to transmit them. They are an electric wave and a magnetic wave coupled together. ELECTROMAGNETISM AN ELECTRIC CURRENT IS INDUCED TO FLOW IN A WIRE WHEN THE WIRE CROSSES (CUTS) A MAGNETIC FIELD LINE A MAGNETIC FIELD IS SET UP EVERY TIME A CURRENT FLOWS IN A WIRE An antenna uses this principle LIGHT IS AN EM WAVE • A MOVING ELECTRIC FIELD INDUCES A MAGNETIC FIELD AT RIGHT ANGLES TO IT. • A MOVING MAGNETIC FIELD INDUCES AN ELECTRIC FIELD, AND SO ON. • MAXWELL CALCULATED THAT THIS PROCESS WOULD TRAVEL ON SPACE AT 3x108 M/S (THE SPPED OF LIGHT) ELECTRICITY TRANSFORMERS CHANGE VOLTAGE GENERATORS (DYNAMOS) CHANGE MECHANICAL MOTION INTO ELECTRICAL POWER MOTORS CHANGE ELECTRICAL POWER INTO MECHANICAL MOTION DIODES ANODE FILAMENT CATHODE A RECTIFIER CURRENT AC TRIODES ANODE FILAMENT CURRENT CATHODE GRID AN AMPLIFIER SIGNAL TO BE AMPLIFIED SOLID STATE PHYSICS CRYSTALS CRYSTALS SYMMETRY TRANSLATIONAL ROTATIONAL (AXIAL) MIRROR (PLANAR) NONE Allowed Electron Energy Levels For an Atom 4+3 2 1 0 Electrons are allowed to occupy a limited set of energy levels only two electrons per level (spin up and spin down. ELECTRONIC BANDS ALLOWED E-STATES BANDS BAND GAP INDIVIDUAL ATOMS As the atoms are moved closer IN together the allowed CRYSTALS e-states must spead out so that there are only 2 electrons per level ELECTRONS IN SOLIDS In solid materials, the electrons in the outer orbits are free to move about as if there is an “electron gas”. But these electrons are restricted to certain allowed allowed energy levels. CONDUCTORS AND INSULATORS AN INSULATOR IS A MATERIAL WHERE ALL THE ALLOWED ELECTRONIC STATES IN THE “VALANCE BAND” ARE OCCUPIED AND THERE IS A FORBIDDEN BAND ABOVE A CONDUCTOR HAS A HALF-FILLED VALANCE BAND WITH MANY AVAILABLE STATES ABOVE FOR ELECTRONS TO MOVE INTO AND THROUGH SEMICONDUCTORS A SEMICONDUCTOR IS LIKE AN INSULATOR BUT THE FORBIDDEN BAND IS NARROW ENOUGH FOR ELECTRONS TO JUMP UP INTO WITH THE HELP OF AN APPLIED VOLTAGE. WHEN AN ELECTRON JUMPS UP TO THE “CONDUCTION BAND”, IT LEAVES A +VE CHARGED “HOLE” IN THE VALANCE BAND. DOPING PUTS IMPURITIES IN THE CRYSTAL SO THAT IT HAS A SURPLUS OF ELECTRONS OR A DEFICIT (HOLES) TRANSISTORS +/- SIGNAL + -------- +++++ ---------- +++++++++ ++++++++++++++++++++ ++++++++++++++++++++ - INTEGRATED CIRCUITS MEMORY CHIPS MOORE’S LAW 108 Pentium III 107 Transistors/chip 106 Chip density doubles every 18 months 105 104 103 1970 Cost of processing plant rises more quickly. By 2010, chip foundry will cost $100B. 1980 Year 1990 2000 SUPERCONDUCTIVITY IN A SUPERCONDUCTOR, THE ELECTRONS LINK UP SO THAT THEY MOVE THROUGH THE SUPERCONDUCTOR WITH NO RESISTANCE. IMAGINE AN ARMY MARCHING ALL LINKED ARMS. THEY WILL NOT NOTICE ANY SMALL ROCKS OR BARRIERS AS THE GROUP CARRIES ON, DESPITE ANY SMALL OBSTRUCTIONS TO ANY ONE MEMBER.