10/27/20101Announcements• HW 10 is available• This week’s HW uses simulations (plan for this), reminder due Friday at midnightReading Quiz on Thursday V=0Voltage Difference is measure of how much energy you need to add (work) or how much energy is released when charged object to go from one place to another.If you need to add energy, then increase in Electrostatic Potential Energy (EPE)If energy is released, then decrease in Electrostatic Potential Energy (EPE)Change in EPE = charge x voltage difference = qV(like G. P. E. with charge instead of mass, V instead of h)--q--no voltage difference between plates. No change in EPE to move from one to other.----------++++++++++Vq--qChange in EPE = qV . Suppose V = +100Volts differenceIf Charge = q = 2 electrons = -2 charges x (1.6 x 10-19C/charge)then … Change in EPE= -3.2x10-19Coulombs x (100Volts) = -3.2 x 10-17J.After charged object hits plate, where did this energy go? a. Kinetic Energy b. Thermal Energy c. Gravitational PEd. Pressure PEVoltage DifferenceChange in Electrostatic PE = charge x voltage difference = qVb. Thermal energy. But just before hit, kinetic so qV=1/2 mv2Next few classes: Flashlights, circuits, batteries, and power• Given a bunch of batteries, light bulbs, and wire, how to design light bulb: that will burn brightest, or that will last longer, or that will be dim, or that will turn on and off. • How can you control and predict current and power in light bulbs? • All this basic circuit stuff applies to home wiring, hair dryers, heaters, all home electronics, etc.• Thursday lecture … help save lives … physics of dangers of electrocution. Builds on electrostatics (like charges repel, opposite charges attract)… electrons can move … circuits are all about electron flow … need to start thinking like an electron! 1. What will happen when hook up battery to flashlight bulb with one wire?a. light up b. barely light up c. not light up What are basic conditions for electric current to flow and lightbulb to light up? +-1. What will happen when hook up battery to flashlight bulb with one wire?a. light up b. barely light up c. not light up What are basic conditions for electric current to flow and lightbulb to light up? Answer is c. Does NOT light up. No where for electrons to flow!!! Electrons in wire attracted to positive end of battery but just stop when all parts of wire equally positive.++++++Now excess positive charges here and all along wire because some electrons left+++++++-10/27/201021. What about hooking up battery to outside of flashlight bulb?a. light up b. barely light up c. not light up What are basic conditions for electric current to flow and lightbulb to light up? Answer is c. Does NOT light up. Still no where for electrons to flow!!! Negative end of battery has whole pile of electrons crowded together some push into wire but again stop when all parts of wire equally negative.Now excess negative charges here and all along wire because some electrons left+-1. What will happen when hook up battery to flashlight bulb with one wire?a. light up b. barely light up c. not light up What are basic conditions for electric current to flow and lightbulb to light up? +-Battery provides energy to push electrons around circuit.Electrons have to be able to flow all the way around and back into battery. Otherwise will pile up and push back(Coulomb's law) preventing any more from flowing.Switch applet.show signal appletElectrons flowing then there is Current (I)Not flowing, then no current (I=0 amps)----------++++++++++Voltage Difference is measure of how much energy you need to add (work) or how much energy is released when a charge moves across voltage difference.Releases energyeeeTakes energyVoltage difference between ends of battery… 1.5 Volts, 9 Volts, 12 VoltsChange in Electrostatic PE = charge x voltage difference = qVWhat happens to EPE as electrons flow? A EPE is always the same.B EPE increases during 1; EPE decreases during 2. C EPE decreases during 1; EPE increases during 2. Stage 1Stage 2eAnswer is b. Takes energy to move electron (negative charge)Release energy as moves back to positive. a. Light will not light up, No current will flow b. Light will light up, Current will flowc. Light will barely light up, Current will flowd. Light will not light up, Current will flowe. Light will light up, No current will flow.back to signal and battery applets for review as neededa. Light will not light up, No current will flow b. Light will light up, Current will flowc. Light will barely light up, Current will flowd. Light will not light up, Current will flowe. Light will light up, No current will flow.d. Light will not light up, Current will flow …THINK LIKE AN ELECTRON! a. Light will not light up, No current will flow What makes light bulb hot and bright? a. Electrons pass through really fast, so they are moving fast, produce light.b. Electrons run into stuff in filament, transfer energy.c. Electrons in filament repelled by electrons flowing through so escape and produce light. Answer is b. Electrons run into stuff in filament, collide … EPE energy to kinetic energy .. then turned into thermal energy … . Show simulation.10/27/20103Circuits – Think like an electronlots of energyat start. Exhausted! energy used up gettingthrough course.Light Bulb… high resistance like trudging through three feet of mud! takes lots of energy to get through. R (rottenness)Wires: glide down pretty easily, just a few bumps. Lose a little bit of energy.eIf there is a reason and a way to flow … electrons will find it!Rules:- No Passing- No electron man deaths on route+-eee eeeee eeeee eeeee eeeee ee e eee eeee eeeee eeeee eeeee ee e eeeeeeeeeeeeRtotal= Rlight+ RwiresUsuallyvery smallElectron man!Circuits – Think like an electronlots of energyat start. Light Bulb… high resistance like trudging through three feet of mud! takes lots of energy to get through. R (rottenness)Wires: glide down pretty easily, just a few bumps. Lose a little bit of energy.eIf there is a reason and a way to flow … electrons will find it!Rules:- No Passing- No electron man deaths on routeRemember to go faster (higher current) uses up more energy (V) so higher I leads to higher Power = I x V_drop+-eee eeeee eeeee eeeee eeeee ee e eee eeee eeeee eeeee eeeee ee e eeeeeeeeeeeeRtotal= Rlight+ RwiresUsuallyvery smallElectron man!Resistance is measure of how hard it is for