1Copyright 2001, Regents of University of CaliforniaLecture 2: 01/29/03 A.R. NeureutherVersion Date 01/30/03EECS 42 Intro. electronics for CS Spring 2003EECS 42 Introduction to Electronics Andrew R. NeureutherLecture #2• Announcements• HKN Tutoring• Discussion 103 Th 3 likely on• HW #1 50x2; plot 0 to 0.010• Use newsgroup on web page• EE43 Read Lab; do Prelab; no Tu• Charge, Current, Energy, Voltage• Powerhttp://inst.EECS.Berkeley.EDU/~ee42/Copyright 2001, Regents of University of CaliforniaLecture 2: 01/29/03 A.R. NeureutherVersion Date 01/30/03EECS 42 Intro. electronics for CS Spring 2003Game Plan 01/22/03Today 01/27/03 Electrical QuantitiesSchwarz and Oldham: 1.3-1.4Wednesday 01/29/03 Kirchhoff LawsSchwarz and Oldham: 2.1-2.2Problem Set #1 - Out 1/22/03 - Due 1/29/03 2:30 in box near 275 CoryPractice Skills needed for Electronics without Electronics1.1 Flow; 1.2 Potential; 1.3 Truth Table; 1.4 GraphsProblem Set #2 – Out 1/27/03 - Due 2/5/03 2:30 in box near 275 Cory2.1 Flow; 2.2 KCL; 2.3 KVL; 2.4 Resistor circuit and I vs. V; 2.5 PowerDiscussion Sections:Copyright 2001, Regents of University of CaliforniaLecture 2: 01/29/03 A.R. NeureutherVersion Date 01/30/03EECS 42 Intro. electronics for CS Spring 2003REVIEW OF ELECTRICAL QUANTITIES AND BASIC CIRCUIT ELEMENTS• Solids in which outer-most atomic electrons are free to move around are called metals.– Metals typically have ~ 1 “free electron” per atom (~ 5 X1022/cm3)– Charge on a free electron is −”e” or “q”, where |e| = 1.6 x 10-19CFree ChargeMost matter is macroscopically electrically neutral most of the time. Exceptions: clouds in thunderstorm, people on carpets in dry weather, plates of a charged capacitor, etc.Microscopically, of course, matter is full of charges. Consider solids:Al or Cu – good metallic conductor – great for wiresSi or GaAs –classic semiconductorsQuartz – good insulator – great for dielectric• Solids in which all charges are bound to atoms are called insulators.• Semiconductors are insulators in which electrons are not tightly bound and thus can be easily “promoted” to a free state (by heat or even by “doping” with a foreign atom).C stands for the units of charge called CoulombCopyright 2001, Regents of University of CaliforniaLecture 2: 01/29/03 A.R. NeureutherVersion Date 01/30/03EECS 42 Intro. electronics for CS Spring 2003CHARGE (cont.)Charge flow ➠ Current Charge storage ➠ Energy, informationDefinition of current i (or I)Note: Current has sign==SC dtdq (A) i secondper coulomb1offlow Amperes)(iniwhere q is the charge in coulomb and t is the time in secExamples:(a)right) (left toA 165106.191019106.1510i nanosecondevery direction) (right toflow19106.1 valueof chargesunit positive 510µ=−×=−−××=+−×=AxCeright) (left to mA6.13106.161016106.11010-idmicroseconevery a wire inright flow to electrons 1010 −=−×−=−−××=(b)Copyright 2001, Regents of University of CaliforniaLecture 2: 01/29/03 A.R. NeureutherVersion Date 01/30/03EECS 42 Intro. electronics for CS Spring 2003Units and mulitpliersWe use metric (“SI”) units in electrical engineering.The important ones are:Energy - E Joules (J)Power - P Watts (W)Charge - Q Coulomb (C )Current - I Ampere (A)Potential - V Volt (V)Resistance - R Ohm (Ω)(V/I)Capacitance - C Farad (F) (C V)Inductance - L Henry (H) (Vsec/A)PREFIXfemto f 10-15pico p 10-12nano n 10-9micro m 10-6milli m 10-3kilo k 103mega M 106giga G 109Copyright 2001, Regents of University of CaliforniaLecture 2: 01/29/03 A.R. NeureutherVersion Date 01/30/03EECS 42 Intro. electronics for CS Spring 2003POSSIBLE CONCEPTUAL ISSUES1 How does charge move through the wire?Remember a wire has a huge number of free carriers moving very fast but randomly (because of thermal energy)<v> ~ C/1000 at 20ºCDrift concept: Now add even a modest electric fieldCarriers “feel” an electric field along the wire and tend to drift with it (+ sign charge) or against it (− charge carrier). This drift is still small compared to the random motion.2 Sign of the charge carriers: It is often negative (for metals); in silicon, it can be either negative or positive.Ben Franklin: Picked/guessed that carriers in wires have a positive sign and move with the electric field. In fact electrons have a negative charge and go the other way (in a positive field). But of course the current is the same for either + or – Q since they move in opposite directions in a given field.2Copyright 2001, Regents of University of CaliforniaLecture 2: 01/29/03 A.R. NeureutherVersion Date 01/30/03EECS 42 Intro. electronics for CS Spring 2003POSSIBLE CONCEPTUAL ISSUES (con’t)4. Field or Current can have positive or negative sign.Examples: I = 0.2 mA same as I = −0.2 mAÆÅ3. Modern Definition re signs: Electric field is in the direction positive charge carriers move. Thus if we have an electrical field in the Z direction, positive charges (ions, positrons, whatever) will experience a force in the positive Z direction. Negatively charged particles will experience the force in the –Z direction. Thus the free carriers we will be concerned with (electrons withnegative charge and “holes” with positive charge) will move against and with the electric field respectively. (Think about hooking up an ammeter and then reversing its connection. The sign of the current it reads must change.)Copyright 2001, Regents of University of CaliforniaLecture 2: 01/29/03 A.R. NeureutherVersion Date 01/30/03EECS 42 Intro. electronics for CS Spring 2003POSSIBLE CONCEPTUAL ISSUES (con’t)5. When we have unknown quantities such as current or voltage, we of course do not know the sign. A question like “Find the current in the wire” is always accompanied by a definition of the direction: 6. Thus there is no need to guess the reference direction so that the answer comes out positive….Your guess won’t affect what the charge carriers are doing! Of course you will find that your intuition and experience will often guide you to define a current direction so that the answer comes out positive. In this example if the current turned out to be 1mA, but flowing to the left we would merely say I = -1mA.(or)IICopyright 2001, Regents of University of CaliforniaLecture 2: 01/29/03 A.R. NeureutherVersion Date 01/30/03EECS 42 Intro. electronics for CS Spring 2003THINKING
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