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If my voltage goes across,\nthat Zener diode goes", "up slightly, the current\nshoots up.", "But if the voltage becomes\nnegative, I don't have any", "current flowing through it until\nthe voltage passes some", "threshold, at which point my\ncurrent begins to build up.", "So you can increase voltage a\nlittle bit, and you can show", "that the current starts\nbuilding up again.", "So that's another interesting\nlumped element", "called a Zener diode.", "Let's switch to the next\none called a diode.", "So a diode looks like this--", "i, v. If the voltage across the\ndiode becomes positive,", "around 0.6 volts or thereabout,\nthe current begins", "to shoot up.", "But if the voltage is below that\nthreshold of 0.6, then my", "current is almost zero.", "It's another lumped element\ncalled a diode.", "And you will begin using these\nelements in your 002 lives to", "build interesting systems.", "Next example is a thermistor.", "A thermistor is a resistor whose\nresistance varies with", "temperature, OK?", "So this is a very expensive\nlittle drier, hair drier.", "And what I'm going to do is\nblow some hot air at my", "resistor, and you're going to\nsee that its value is going to", "change depending on how\nmuch I heat it.", null, "As it cools down--", "let me cool it down.", null, "So you can see it's\ncoming down.", "I can zap it again.", "[TURNS ON DRYER]", "ANANT AGARWAL: I could\ndo this all day.", "This is so much fun.", "[LAUGHTER]", "ANANT AGARWAL: OK, so\nthat's a another", "interesting lumped element.", "As the temperature rises,\nits resistance changes.", "LORENZO: Photo.", "ANANT AGARWAL: Next thing is\ncalled a photoresistor.", "It's a resistor.", "It used to be a resistor,\nLorenzo?", "LORENZO: Yeah.", "OK, that's fine.", "ANANT AGARWAL: So this\nis a photoresistor.", "And notice that it almost\nbehaves like an open circuit.", "Well, what I'm going to do is\nshine some light on it.", null, "When I shine light on it, it\nbegins to conduct and becomes", "a resistor of some value.", null, "There you go, OK?", "So that's a photoresistor.", "LORENZO: Now, we go to the--", "ANANT AGARWAL: So now I'm going\nto show you a battery.", "Notice, we didn't talk about\nbatteries before.", "I'll show you a battery.", "So before we show a battery,\njust think in your own minds,", "what should the iv\ncharacteristic of a", "battery look like?", "i, v, a battery supplies\na constant voltage.", "You know, your little\ncell, your double A", "battery, 1.5 volts?", "So think about what the iv\ncharacteristic of a battery", "should look like for three\nseconds before", "I show it to you.", "And so I show it, Lorenzo.", null, "It's a straight line.", "This is a good battery.", "It's a straight vertical line,\nwhich says that the voltage is", "1.5 volts or thereabouts\nno matter", "what current it supplies.", "As an ideal voltage source, it\nas a fixed voltage v no matter", "what the current going\nthrough it is.", "Now I'll show you a dud,\na bad battery.", "And this is what the bad\nbattery looks like.", "So many of you had a your car\nbatteries die on you, and when", "you go to the store, they\ncheck your batteries.", "They use exactly this principle,\nthat dead batteries", "have resistance.", "Whenever you see slopes here,\nyou're thinking of resistance,", "They can use this property\nto figure out that", "your battery is dead.", "So that's a dead battery.", "And finally, let me\nshow you a bulb.", "We started with a bulb,\nand so I need to end--", "OK.", "We started with a bulb, so we\nneed to end with a bulb.", "And what you'll see is that\na bulb is simply--", "behaves like a resistor.", "It's iv curve is going\nto look like this.", "OK, notice, this is my\nbulb, and guess what?", "It behaves like a resistor.", "It's a very interesting\nkind of resistor.", "So I won't go into details for\nnow, but notice its iv", "characteristic behaves\nlike a resistor, OK?", "So those are some pretty\nstandard lumped elements.", "You'll deal with a lot more\nset of lumped elements--", "switches, MOFETs, capacitors,\ninductors, a bunch", "of other fun stuff.", "But before we do that, what I\nwanted to tell you is that", "don't go berserk on this\nabstraction binge, OK?", "Too much of anything\nis bad for you.", "So what I'm going to show you is\nabstractions or models are", "only valid provided you work\nwithin a set of constraints.", "Notice, we've already had this\ntacit handshake, which said", "that we'll follow the\ndiscipline, OK?", "Even after we follow the\ndiscipline, there are ranges", "to how well physical elements\ncan behave like", "ideal lumped elements.", "For example, what I'm going to\ndo is show you as a resistor.", "And it's going to look like a\nresistor, and I'm going to", "keep increasing the voltage around it.", "What's going to happen\nat some point?", "I just keep doing that.", "If it's an ideal element, if\nyou're a theorist, you'll say,", "oh yeah, the curve will\nkeep extending", "until I reach infinity.", "But this is a practical\nresistor, so, you know.", "The people out here, you're\ngoing to have to cover your", "eyes or something.", null, "So your abstraction\ncan't predict that.", null, "It says the current is an amp.", "It can predict the heat,\nlight, or the smell.", "Because in the laboratory, when\nyou get the smell, you", "know what somebody\nhas just done.", "They blown the resistor.", "So that's one example\nof a lumped", "abstraction breaking down.", "So if I really believe in my\nown BS, anything's a lumped", "element, so here's a pickle.", "[LAUGHTER]", "ANANT AGARWAL: A pickle's\na lumped element.", "I can treat it as a\nlumped resistor.", "But this is a very interesting\nlumped resistor.", "[LAUGHTER]", "ANANT AGARWAL: Don't\ntry this at home.", "This is a standard pickle\ninto which we are", "pumping 110 volts AC.", "[LAUGHTER]", "ANANT AGARWAL: I promise you,\nthis is a standard pickle.", "So as you can tell, it has a\nfixed resistance, but your", "lumped abstraction cannot\npredict the nice light and", "sound effect.", "[LAUGHTER]" ] }