0:00:01.270,0:00:05.030 Now let's talk about circuit elements[br]in a little bit different way. 0:00:05.030,0:00:06.660 Let's talk about realistic voltage and 0:00:06.660,0:00:10.700 current sources and i-v curves[br]associated with common elements. 0:00:10.700,0:00:11.560 Let's talk about open and 0:00:11.560,0:00:14.970 short circuits and switches,[br]particularly wiring three-way switches. 0:00:16.050,0:00:19.150 An ideal voltage and[br]current source has no resistance. 0:00:19.150,0:00:23.580 The voltage source just produces voltage,[br]the current source just produces current. 0:00:23.580,0:00:27.820 But a more realistic non-ideal voltage[br]source and current source has resistance. 0:00:27.820,0:00:30.190 A voltage source has[br]a resistor in series and 0:00:30.190,0:00:34.055 a current source has a resistance in[br]parallel, called the shunt resistance. 0:00:34.055,0:00:37.270 You know that most of your sources[br]are realistic because they heat up when 0:00:37.270,0:00:37.906 you use them. 0:00:37.906,0:00:41.225 Your power drill, for example,[br]gets hot when you use it very long, 0:00:41.225,0:00:43.708 and that's because of[br]its internal resistance. 0:00:43.708,0:00:46.680 Here is a graph of the internal[br]resistance of a battery. 0:00:46.680,0:00:50.840 Batteries get hot when we use them too,[br]certainly my laptop battery does. 0:00:50.840,0:00:55.710 So you can see that this battery,[br]this is an Energizer 1.5 volt AA battery. 0:00:55.710,0:00:59.320 As the temperature changes, so[br]does its internal resistance. 0:00:59.320,0:01:04.220 Its internal resistance is just going to[br]be, oops, I want it to go up, not down, 0:01:04.220,0:01:08.420 is going to just be this series resistance[br]that's right here with a battery. 0:01:08.420,0:01:09.940 So let's take a look. 0:01:09.940,0:01:12.290 Now, if you were at room temperature, 0:01:12.290,0:01:16.720 the internal resistance of that[br]battery would be about 0.15 ohms. 0:01:16.720,0:01:21.492 And if you were in Antarctica, which[br]is where I did some measurements, and 0:01:21.492,0:01:25.282 let's say that you were about[br]-10 degrees centigrade, 0:01:25.282,0:01:28.497 then your resistance[br]would be about 0.3 ohms. 0:01:28.497,0:01:30.790 Let's see how that affects you. 0:01:30.790,0:01:34.055 Let's suppose that you just want[br]to hook up this battery with its 0:01:34.055,0:01:36.650 internal resistance to a very small load. 0:01:36.650,0:01:40.277 I'm going to use a 1-ohm load for[br]this example. 0:01:40.277,0:01:43.917 I would find the current that's in[br]the circuit by taking the voltage and 0:01:43.917,0:01:46.500 dividing by the sum of the two resistors. 0:01:46.500,0:01:51.370 So in this case, if I had an ideal source,[br]it would be 1.5 volts divided by my 0:01:51.370,0:01:57.020 1 ohm load, and so I would have[br]1.5 amps for the ideal battery. 0:01:57.020,0:01:59.290 But now let's say that[br]I'm at room temperature. 0:01:59.290,0:02:04.082 In that case, my internal resistance is[br]0.15, so if I add that right in here to my 0:02:04.082,0:02:07.440 1 ohm, I'm going to have 1.3[br]amps at room temperature. 0:02:07.440,0:02:10.810 It's a little less than I had for[br]my ideal battery. 0:02:10.810,0:02:13.959 Now let's go to my Antarctica battery, and 0:02:13.959,0:02:18.727 that's where I have 0.3 ohms[br]connected on to my 1 ohm load, and 0:02:18.727,0:02:23.174 I have 1.15 Amps,[br]than I really intended to have 1.5. 0:02:23.174,0:02:25.090 So what did that do? 0:02:25.090,0:02:28.400 This is why our batteries went dead so[br]fast in the Antarctic cold. 0:02:30.440,0:02:32.610 Now let's talk about I-V curves. 0:02:32.610,0:02:35.960 Here are the I-V curves for[br]the simple circuit that I just showed you. 0:02:35.960,0:02:38.620 You have a battery[br]connected onto a resistor. 0:02:38.620,0:02:42.140 And what we would be plotting[br]is voltage on the x axis and 0:02:42.140,0:02:44.930 current, or I, on the y axis. 0:02:44.930,0:02:48.100 The I-V curve for[br]a resistor is always a straight line. 0:02:48.100,0:02:50.560 The resistor is a linear device. 0:02:50.560,0:02:53.370 If I had a 1 kiloohm resistor,[br]for example, 0:02:53.370,0:02:58.000 connected onto a 1 volt battery,[br]I would have 1 milliamp of current. 0:02:58.000,0:03:02.190 If I had a 2 kiloohm resistor,[br]I'd have half a milliohm of current. 0:03:02.190,0:03:04.360 And if I had a really high resistance, 0:03:04.360,0:03:08.100 let's say infinity,[br]I would have no current at all. 0:03:08.100,0:03:12.050 On the other hand, if I had a very[br]tiny resistor, let's say 0 ohms, 0:03:12.050,0:03:15.900 I would have no voltage, but[br]I'd have a very large current. 0:03:15.900,0:03:17.510 What does that mean? 0:03:17.510,0:03:20.340 Having a resistor of 0 is a short circuit. 0:03:20.340,0:03:24.110 That's where my current runs away with me,[br]I have a huge current, and 0:03:24.110,0:03:26.050 my voltage would be 0. 0:03:26.050,0:03:30.060 An open circuit has a very high[br]resistance, resistance of infinity, and 0:03:30.060,0:03:33.840 in that case, you have no current,[br]but you have a very large voltage. 0:03:36.070,0:03:39.450 The I-V curves for an LED are non-linear. 0:03:39.450,0:03:43.780 The LED is a little light bulb that turns[br]on when we put a voltage across it. 0:03:43.780,0:03:47.100 We're going to be using it in our first or[br]second lab. 0:03:47.100,0:03:51.500 So you can see right here that there[br]are different colors of LEDs and that 0:03:51.500,0:03:56.040 as the voltage increases for each one,[br]see here's, I'm turning up the voltage, 0:03:56.040,0:03:59.490 turning up the voltage, and[br]the current becomes very high. 0:03:59.490,0:04:03.920 This elbow right here,[br]where the current goes from being almost 0 0:04:03.920,0:04:08.480 to becoming almost its final value,[br]it's called the forward turn on voltage. 0:04:08.480,0:04:09.960 And right here for the red one, 0:04:09.960,0:04:15.230 you can see the forward turn on[br]voltage for a red LED is about 1 volt. 0:04:15.230,0:04:18.622 The turn on voltage for[br]a white LED would be a little bit higher. 0:04:21.408,0:04:25.140 Now let's go back to our idea of[br]the open circuit and the short circuit. 0:04:25.140,0:04:27.355 If I have an open circuit,[br]my current is 0. 0:04:27.355,0:04:31.922 My circuit may not work, but[br]at least it's not gonna run away with me. 0:04:31.922,0:04:35.561 My short circuit, on the other hand,[br]has a very small resistance but 0:04:35.561,0:04:37.315 extremely high current. 0:04:37.315,0:04:39.165 That's what can actually[br]do you some damage. 0:04:41.485,0:04:45.355 A fuse or a circuit breaker is what's[br]intended to keep the current from running 0:04:45.355,0:04:45.946 away with you. 0:04:45.946,0:04:46.726 If the current was trying[br]to go to infinity, but 0:04:46.726,0:04:52.070 we had a 10-amp circuit breaker in line[br]with that, the circuit breaker would 0:04:53.470,0:04:57.678 trip when the current got to 10 amps and[br]it would shut the circuit off. 0:04:57.678,0:05:01.037 A circuit breaker is a type of switch. 0:05:01.037,0:05:03.595 There's several other types of switches. 0:05:03.595,0:05:06.653 The most common that we use when[br]we do our designs are single pole, 0:05:06.653,0:05:08.160 single throw switches. 0:05:08.160,0:05:12.140 That's just a switch that you just[br]turn on, turn off, turn on, turn off. 0:05:12.140,0:05:15.610 The other is a single pole double throw,[br]where you turn on here or 0:05:15.610,0:05:19.810 you turn on there, turn on here, turn on[br]there, and there are many others as well. 0:05:19.810,0:05:23.030 I put a link on the website, and I thought[br]it was pretty interesting for you to see 0:05:23.030,0:05:26.270 all the different kinds of switches that[br]you might be using throughout your career. 0:05:27.730,0:05:32.636 One very interesting switch circuit is[br]the three-way light switch, that's where 0:05:32.636,0:05:37.360 you have a voltage source connected on to[br]two single pull double throw switches. 0:05:37.360,0:05:39.250 These are very common along stairways or 0:05:39.250,0:05:42.310 hallways, because you want to[br]able to turn the light on or 0:05:42.310,0:05:47.190 off from the top of the stairs as well[br]as from the bottom of the stairs. 0:05:47.190,0:05:49.700 Now right here in the circuit,[br]you'll notice that these two 0:05:49.700,0:05:53.760 switches have to be connected by a double[br]set of wires going between them, 0:05:53.760,0:05:58.710 and then they're connected on to the lamp[br]or the light bulb along a neutral line. 0:05:58.710,0:06:01.340 We often choose to use the light[br]bulb in the neutral line 0:06:01.340,0:06:02.760 instead of the power line. 0:06:02.760,0:06:05.880 Because in the event that someone[br]was taking the lightbulb out, and 0:06:05.880,0:06:08.900 let's say that they accidentally[br]got their finger or 0:06:08.900,0:06:12.090 maybe a piece of or[br]maybe a tool across here. 0:06:12.090,0:06:14.674 And somehow they managed to[br]short themselves to a live line, 0:06:14.674,0:06:17.560 sorry to the ground. 0:06:17.560,0:06:20.330 If we were connected to the neutral,[br]nothing should happen, but 0:06:20.330,0:06:22.610 if they were connected to a live line,[br]it should. 0:06:22.610,0:06:25.630 So most often, the lamp is put[br]on the neutral line for safety. 0:06:27.630,0:06:31.620 So in conclusion today, we've talked about[br]voltage and current sources, open and 0:06:31.620,0:06:33.340 short circuits, and switches. 0:06:33.340,0:06:36.310 I'd like you to take a minute[br]to try the three-way switch 0:06:36.310,0:06:38.020 in your MultiSim simulation. 0:06:38.020,0:06:40.220 It's a good chance to get[br]to practice with MultiSim. 0:06:40.220,0:06:44.060 And it's fun to see how[br]the three-way switch works. 0:06:44.060,0:06:46.370 Now, let's talk about where[br]the picture was in the front. 0:06:46.370,0:06:49.050 This is the Sunflowers &[br]Thunderheads picture from 0:06:49.050,0:06:51.860 Blackhawk Trail In Payson Canyon, Utah. 0:06:51.860,0:06:53.960 See all these yellow[br]sunflowers along here? 0:06:53.960,0:06:55.010 It's absolutely amazing. 0:06:55.010,0:06:57.576 This is normally the week[br]of the Fourth of July.