1 00:00:00,000 --> 00:00:05,000 Now we've learned all about series and parallel circuits and we're ready to see how our houses are wired. 2 00:00:05,000 --> 00:00:07,000 The model of a house right here. 3 00:00:07,000 --> 00:00:10,000 How can we tell whether it's wired in series or in parallel? 4 00:00:10,000 --> 00:00:13,000 Well, we know that when something is wired in parallel, 5 00:00:13,000 --> 00:00:16,000 when one lamp burns out or is turned off, the rest of them stay on. 6 00:00:16,000 --> 00:00:19,000 Not only that, but the lights that are still on don't change. 7 00:00:19,000 --> 00:00:22,000 They don't get lighter and they don't get dimmer. 8 00:00:22,000 --> 00:00:26,000 Let's try it. Let's turn one of these lamps off and see what happens. 9 00:00:26,000 --> 00:00:28,000 They must be in parallel because in series, 10 00:00:28,000 --> 00:00:31,000 all of the lights would have gone out when one was turned off. 11 00:00:31,000 --> 00:00:34,000 Why is it important to have a house wired in parallel? 12 00:00:34,000 --> 00:00:37,000 Well, it'd be really annoying if I was playing on the computer 13 00:00:37,000 --> 00:00:40,000 and my dad turned a lamp off and the computer shut off. 14 00:00:40,000 --> 00:00:42,000 Or if I was in my room and my light got dimmer 15 00:00:42,000 --> 00:00:45,000 because someone else was turning lights on in the house. 16 00:00:45,000 --> 00:00:48,000 As more and more devices are turned on in the house, 17 00:00:48,000 --> 00:00:51,000 the number of charges flowing through the circuit increases. 18 00:00:51,000 --> 00:00:54,000 Each device gets just the current that it needs, 19 00:00:54,000 --> 00:00:58,000 but the current flowing in the supply wires must supply current to all the devices. 20 00:00:58,000 --> 00:01:00,000 If too many devices are turned on, 21 00:01:00,000 --> 00:01:03,000 the current in the supply wires is too great and the wires get hot. 22 00:01:03,000 --> 00:01:05,000 This is called an overload. 23 00:01:05,000 --> 00:01:07,000 The circuit breaker trips and turns the circuit off. 24 00:01:07,000 --> 00:01:10,000 I guess the circuit breaker is in series with everything else. 25 00:01:10,000 --> 00:01:13,000 When it is turned off, we have an open circuit. 26 00:01:13,000 --> 00:01:15,000 Why would you want everything in the circuit to turn off? 27 00:01:15,000 --> 00:01:17,000 Because if the wires in the walls get too warm, 28 00:01:17,000 --> 00:01:19,000 then you'd have a fire on your hands. 29 00:01:19,000 --> 00:01:20,000 That's right. 30 00:01:20,000 --> 00:01:24,000 Now sometimes an appliance malfunctions and causes a short circuit. 31 00:01:24,000 --> 00:01:27,000 It basically means the two incoming wires touch. 32 00:01:27,000 --> 00:01:30,000 There's a huge current that runs through because it's bypassing the load. 33 00:01:30,000 --> 00:01:33,000 Now when a short circuit occurs, what happens? 34 00:01:33,000 --> 00:01:36,000 So the circuit breaker opens the circuit, so no harm is done. 35 00:01:36,000 --> 00:01:38,000 That's right, just like this. 36 00:01:38,000 --> 00:01:41,000 So when a circuit breaker is tripped, you have to first fix the problem 37 00:01:41,000 --> 00:01:43,000 and turn the circuit breaker back on. 38 00:01:43,000 --> 00:01:46,000 Just like several wall outlets in a house are connected together 39 00:01:46,000 --> 00:01:48,000 and protected by a circuit breaker, 40 00:01:48,000 --> 00:01:52,000 the houses in a neighborhood are also connected together in this parallel circuit 41 00:01:52,000 --> 00:01:54,000 and protected by a big circuit breaker. 42 00:01:54,000 --> 00:01:56,000 So how many houses are in a circuit? 43 00:01:56,000 --> 00:01:58,000 Could be as many as four or five. 44 00:01:58,000 --> 00:02:01,000 Does this mean if there's too much current going into a house in the circuit, 45 00:02:01,000 --> 00:02:03,000 the circuit breaker opens the circuit? 46 00:02:03,000 --> 00:02:06,000 That's right. When the circuit is open, all the houses go dark. 47 00:02:06,000 --> 00:02:08,000 Wow, we may be onto something here. 48 00:02:08,000 --> 00:02:11,000 But what could cause too much current to go to the houses? 49 00:02:11,000 --> 00:02:13,000 I guess the circuit breaker isn't working. 50 00:02:13,000 --> 00:02:17,000 No, I think it's more of a problem with the wires running to the houses. 51 00:02:17,000 --> 00:02:19,000 Maybe there's a short circuit in the wires. 52 00:02:19,000 --> 00:02:20,000 Good thinking. 53 00:02:20,000 --> 00:02:22,000 Why didn't we think of this earlier? 54 00:02:22,000 --> 00:02:25,000 Maybe because the electrical wires in our neighborhood are buried underground. 55 00:02:25,000 --> 00:02:28,000 That way, the short circuit could be hidden from view. 56 00:02:28,000 --> 00:02:30,000 This could be tough. 57 00:02:30,000 --> 00:02:32,000 Hey, Dr. D., have you had any luck with your train? 58 00:02:32,000 --> 00:02:37,000 Nope. I checked out the power unit on the workbench last night, 59 00:02:37,000 --> 00:02:40,000 and it is indeed working. This is really getting puzzling. 60 00:02:40,000 --> 00:02:44,000 Wait a minute. Talking about series and parallel circuits 61 00:02:44,000 --> 00:02:46,000 reminds me of something else to check on the train. 62 00:02:46,000 --> 00:02:47,000 What's that? 63 00:02:47,000 --> 00:02:50,000 Well, the pieces of track form a series circuit. 64 00:02:50,000 --> 00:02:53,000 If one of the links of track is not properly plugged in, 65 00:02:53,000 --> 00:02:55,000 we have an open circuit. The train won't work. 66 00:02:55,000 --> 00:02:57,000 I'll check on that later. 67 00:02:57,000 --> 00:03:00,000 In the meantime, I think we should revise our hypothesis to 68 00:03:00,000 --> 00:03:03,000 there is an open circuit somewhere between the power source 69 00:03:03,000 --> 00:03:05,000 and the houses across the street. 70 00:03:05,000 --> 00:03:07,000 Well, good luck on solving your mystery. 71 00:03:07,000 --> 00:03:09,000 It sounds like you're getting close.