WEBVTT 00:00:00.300 --> 00:00:01.500 - [Lecturer] Electricity that lights up 00:00:01.500 --> 00:00:05.460 above looks very different than lightning strikes, 00:00:05.460 --> 00:00:08.070 but they're actually more similar than one might think 00:00:08.070 --> 00:00:10.470 because they both have electric current. 00:00:10.470 --> 00:00:12.450 So let's understand what electric current is, 00:00:12.450 --> 00:00:13.800 how they're produced, 00:00:13.800 --> 00:00:16.110 and also get to understand a little bit about lightning. 00:00:16.110 --> 00:00:18.120 So what exactly is electric current? 00:00:18.120 --> 00:00:19.140 Well think of electric current 00:00:19.140 --> 00:00:23.190 as a flow of net charge through any given area. 00:00:23.190 --> 00:00:26.520 Here's what I mean by flow of net charge. 00:00:26.520 --> 00:00:28.770 Well imagine you have a tiny cross-sectional area 00:00:28.770 --> 00:00:30.480 through which you have equal amount 00:00:30.480 --> 00:00:31.440 of positive charges flowing 00:00:31.440 --> 00:00:33.870 to the right and left in any given time. 00:00:33.870 --> 00:00:35.430 Now notice there is a flow, 00:00:35.430 --> 00:00:37.260 but there is no net flow (chuckles) 00:00:37.260 --> 00:00:39.990 and therefore here we say there is zero current. 00:00:39.990 --> 00:00:42.900 Another interesting example is what if you have equal amount 00:00:42.900 --> 00:00:45.060 of positive and negative charges flowing 00:00:45.060 --> 00:00:47.430 in the same direction in the same time, let's say 00:00:47.430 --> 00:00:49.680 through again, a given cross-sectional area. 00:00:49.680 --> 00:00:51.840 Again, notice there is a flow of charges, 00:00:51.840 --> 00:00:54.510 but the total flow over here, total charge 00:00:54.510 --> 00:00:55.980 that's flowing is zero. (chuckles) 00:00:55.980 --> 00:00:57.870 So net charge is still zero 00:00:57.870 --> 00:01:00.510 and therefore there is no electric current over here. 00:01:00.510 --> 00:01:05.070 Okay, what about now? Ooh, now we do have electric current. 00:01:05.070 --> 00:01:08.610 Now we have a net positive charge flowing to the right. 00:01:08.610 --> 00:01:10.170 Over here there is an electric current. 00:01:10.170 --> 00:01:13.800 Now we do have a net negative charges flowing to the right. 00:01:13.800 --> 00:01:16.560 We do have an electric current. Okay? 00:01:16.560 --> 00:01:20.940 So it's a flow of net charge, but how do you measure it? 00:01:20.940 --> 00:01:24.540 Well, we measure it as the amount of charges flowing 00:01:24.540 --> 00:01:27.900 through any given cross-sectional area per second. 00:01:27.900 --> 00:01:31.170 So you can think of it as coulomb per second. 00:01:31.170 --> 00:01:35.160 How many coulombs are flowing per second? 00:01:35.160 --> 00:01:37.593 And the coulombs per second is also called, 00:01:38.580 --> 00:01:43.580 it's also called Amperes, okay? Capital A, Amperes. 00:01:43.620 --> 00:01:45.390 And just to give you typical numbers, 00:01:45.390 --> 00:01:47.670 your air conditioners heaters, 00:01:47.670 --> 00:01:50.580 they drop out 10 to 15 Amperes of current. 00:01:50.580 --> 00:01:54.330 Your ceiling fan tube lights, television sets less than 00:01:54.330 --> 00:01:56.130 that, about one or two amps. 00:01:56.130 --> 00:01:59.250 And your smaller circuits like you know the toy circuits 00:01:59.250 --> 00:02:01.470 and stuff, they would be even lesser. 00:02:01.470 --> 00:02:04.404 It would be fraction of Amperes. But what about lightning? 00:02:04.404 --> 00:02:05.460 Ooh. (chuckles) 00:02:05.460 --> 00:02:09.270 Lightning can have tens of thousands of Amperes in them. 00:02:09.270 --> 00:02:11.100 Okay, how do we set up an electric current? 00:02:11.100 --> 00:02:12.450 How do we get an electric current? 00:02:12.450 --> 00:02:16.380 Well, for an electric current we need a voltage. 00:02:16.380 --> 00:02:18.600 Just like how, if you need to make a ball roll, you need 00:02:18.600 --> 00:02:20.910 to have a height difference, 00:02:20.910 --> 00:02:24.330 which produces a gravitational potential difference 00:02:24.330 --> 00:02:26.100 across the end of say a plank. 00:02:26.100 --> 00:02:30.030 Similarly, if you need to set up a current through a wire, 00:02:30.030 --> 00:02:34.110 you need to have an electric potential difference 00:02:34.110 --> 00:02:35.490 across the ends of it. 00:02:35.490 --> 00:02:37.170 When you have an electric potential difference, 00:02:37.170 --> 00:02:39.720 you can get a current, but you also need to make sure 00:02:39.720 --> 00:02:41.700 that there are some charges. 00:02:41.700 --> 00:02:45.150 There are charges that are free to move in your material. 00:02:45.150 --> 00:02:49.050 Not all materials have that, for example, glass or plastic. 00:02:49.050 --> 00:02:50.670 Well, they don't have free charges because 00:02:50.670 --> 00:02:52.860 if you look inside them, well you can model them 00:02:52.860 --> 00:02:54.060 and say that you know what? 00:02:54.060 --> 00:02:57.330 The electrons inside these atoms are very tightly bound. 00:02:57.330 --> 00:02:59.160 So there are no free electrons to move. 00:02:59.160 --> 00:03:00.450 There are no charges to move. 00:03:00.450 --> 00:03:01.283 So if you put a voltage 00:03:01.283 --> 00:03:04.230 across them, you'll probably get no current over here. 00:03:04.230 --> 00:03:07.020 We call such material insulators, glass, 00:03:07.020 --> 00:03:10.920 wood, plastic, these are examples of insulators. 00:03:10.920 --> 00:03:12.510 On the other hand, if you take metals 00:03:12.510 --> 00:03:14.850 of which wires are made of, then you'll find 00:03:14.850 --> 00:03:18.120 that the outermost electrons are not tightly bound. 00:03:18.120 --> 00:03:21.960 As a result, they are free to move around the material. 00:03:21.960 --> 00:03:23.640 We call them free electrons. 00:03:23.640 --> 00:03:25.950 And since you have free charges available 00:03:25.950 --> 00:03:28.218 for motion, we call these materials conductors 00:03:28.218 --> 00:03:30.540 because if you put a voltage across them, 00:03:30.540 --> 00:03:34.260 well these electrons can move and contribute to current. 00:03:34.260 --> 00:03:37.350 So you need a voltage across a conducting medium 00:03:37.350 --> 00:03:39.930 for electric current. 00:03:39.930 --> 00:03:42.750 Okay, but how do you get a voltage in the first place? 00:03:42.750 --> 00:03:45.053 Well, in small circuits, you probably already know, 00:03:45.053 --> 00:03:47.310 voltage is given by a battery. 00:03:47.310 --> 00:03:49.440 One end of the battery is at a higher potential, 00:03:49.440 --> 00:03:51.247 another end of the battery is at lower potential. 00:03:51.247 --> 00:03:53.850 And when you connect it to a circuit, it provides 00:03:53.850 --> 00:03:54.960 the potential difference. 00:03:54.960 --> 00:03:57.480 But in larger circuits for like for example, the circuits 00:03:57.480 --> 00:04:00.330 in our houses, well the potential difference is provided 00:04:00.330 --> 00:04:03.870 by large electric generators in our power stations. 00:04:03.870 --> 00:04:06.870 And by the way, while drawing a battery in our circuit, 00:04:06.870 --> 00:04:09.120 well we use a circuit symbol that looks like this. 00:04:09.120 --> 00:04:12.480 The longer line represents the positive terminal 00:04:12.480 --> 00:04:15.360 and the shorter thick line represents a negative terminal. 00:04:15.360 --> 00:04:16.920 So that if you just draw this, we don't have to draw 00:04:16.920 --> 00:04:18.870 like a big battery over here. 00:04:18.870 --> 00:04:20.460 Anyways, even though we have a battery 00:04:20.460 --> 00:04:23.100 in this circuit right now, we don't have a current, 00:04:23.100 --> 00:04:25.710 we don't have a potential difference across this bulb. 00:04:25.710 --> 00:04:26.580 Why? 00:04:26.580 --> 00:04:27.900 Well, you can see over here, that's 00:04:27.900 --> 00:04:30.390 because the circuit is not closed. 00:04:30.390 --> 00:04:32.970 We say because there is some air in between. 00:04:32.970 --> 00:04:35.520 Air is an excellent insulator and 00:04:35.520 --> 00:04:38.130 therefore there's not going to be any current over here. 00:04:38.130 --> 00:04:40.020 In order for there to be a current, we need 00:04:40.020 --> 00:04:43.410 to close the circuit, meaning we need to connect this gap 00:04:43.410 --> 00:04:45.930 and that's where the switch is, this is a switch. 00:04:45.930 --> 00:04:48.630 So if I close the switch 00:04:48.630 --> 00:04:52.770 like this, now the circuit is complete. 00:04:52.770 --> 00:04:55.320 Now there'll be a potential difference across the ends 00:04:55.320 --> 00:04:58.500 of the ball when now there'll be a current over here. 00:04:58.500 --> 00:05:00.000 I'm gonna open the switch. 00:05:00.000 --> 00:05:02.250 There is no electric current, the circuit is broken. 00:05:02.250 --> 00:05:04.950 Close the switch, there's going to be an electric current. 00:05:04.950 --> 00:05:06.690 Now because I compared charges moving 00:05:06.690 --> 00:05:08.880 through a ball rolling down, we might model it 00:05:08.880 --> 00:05:12.300 by thinking that hey, when there is no voltage, 00:05:12.300 --> 00:05:14.100 all the charges are at rest, say the electrons 00:05:14.100 --> 00:05:16.705 over here are at rest and when I do complete the circuit, 00:05:16.705 --> 00:05:18.780 the electrons are now nicely moving. 00:05:18.780 --> 00:05:20.910 But that's not a very accurate way to think about it, 00:05:20.910 --> 00:05:22.050 that's not a good model. 00:05:22.050 --> 00:05:23.970 Instead, a better model is if you were to peek 00:05:23.970 --> 00:05:26.610 inside the wire, we find that the electrons 00:05:26.610 --> 00:05:28.200 are randomly moving, bumping 00:05:28.200 --> 00:05:29.910 into stuff because they have a lot 00:05:29.910 --> 00:05:32.880 of energy even when there is no voltage. 00:05:32.880 --> 00:05:34.470 So they're not at rest, they're 00:05:34.470 --> 00:05:36.960 in fact moving at very high speeds. 00:05:36.960 --> 00:05:38.760 But what happens when we close the switch? 00:05:38.760 --> 00:05:40.740 When we close the circuit, look, 00:05:40.740 --> 00:05:42.270 there is a potential difference 00:05:42.270 --> 00:05:45.240 and therefore there is an electric field setup in the wire 00:05:45.240 --> 00:05:47.640 that electric field starts pushing on the electrons. 00:05:47.640 --> 00:05:49.080 And look, you can now see the electrons 00:05:49.080 --> 00:05:51.720 are slowly drifting to the left. 00:05:51.720 --> 00:05:56.250 It's that drifting motion that constitutes the current 00:05:56.250 --> 00:05:58.380 and what causes them to drift to the left? 00:05:58.380 --> 00:06:00.030 Again, there are some analogies which says 00:06:00.030 --> 00:06:02.820 that electrons push on each other making them drift. 00:06:02.820 --> 00:06:05.130 But that's again not very accurate. 00:06:05.130 --> 00:06:06.660 A better way to think about it is 00:06:06.660 --> 00:06:08.790 that the battery produces the electric field. 00:06:08.790 --> 00:06:10.590 There's an electric field set up inside the wire. 00:06:10.590 --> 00:06:14.160 It's that electric field that is causing, 00:06:14.160 --> 00:06:16.380 that's pushing the electrons, making them drift 00:06:16.380 --> 00:06:17.850 to the left over here. 00:06:17.850 --> 00:06:19.260 But wait a second, why did I show 00:06:19.260 --> 00:06:22.380 that the electrons are drifting to the left over here? 00:06:22.380 --> 00:06:23.760 Let's think about it. 00:06:23.760 --> 00:06:25.350 So one way to think about it's, you could say 00:06:25.350 --> 00:06:26.670 that hey, electrons are being attracted 00:06:26.670 --> 00:06:29.490 by the positive terminal of the battery being repelled 00:06:29.490 --> 00:06:31.470 by the negative terminal of the battery, making 00:06:31.470 --> 00:06:33.150 the electrons go this way. 00:06:33.150 --> 00:06:34.710 But a question that could raise is, 00:06:34.710 --> 00:06:36.750 in the wire that means the electrons are going 00:06:36.750 --> 00:06:39.510 from a lower potential to a higher potential 00:06:39.510 --> 00:06:40.530 like going uphill. 00:06:40.530 --> 00:06:41.820 How does that make any sense? 00:06:41.820 --> 00:06:43.920 That was a point of confusion for a long time. 00:06:43.920 --> 00:06:46.380 So let's talk about it a little bit. Okay? 00:06:46.380 --> 00:06:48.270 If I have a big positive charge 00:06:48.270 --> 00:06:52.050 and next to it I keep a very tiny positive charge 00:06:52.050 --> 00:06:53.640 and at rest, let's say, 00:06:53.640 --> 00:06:56.220 and I let go of it, then we know it gets repelled 00:06:56.220 --> 00:06:59.070 and it gains kinetic energy in this direction. 00:06:59.070 --> 00:07:01.140 Now because energy is conserved, we could ask where did 00:07:01.140 --> 00:07:02.490 that kinetic energy come from? 00:07:02.490 --> 00:07:06.300 We say, ah, there it must have come from potential energy. 00:07:06.300 --> 00:07:07.860 So as it goes from here to here, 00:07:07.860 --> 00:07:10.410 the system must lose potential energy 00:07:10.410 --> 00:07:12.060 and therefore we can now say that hey, 00:07:12.060 --> 00:07:14.940 this point represents high potential region. 00:07:14.940 --> 00:07:17.490 This point represents low potential region 00:07:17.490 --> 00:07:21.510 and this represents the downhill direction for the charges. 00:07:21.510 --> 00:07:23.280 As you go from here to here, it's potential energy 00:07:23.280 --> 00:07:24.930 starts getting converted into kinetic energy. 00:07:24.930 --> 00:07:27.630 Kind of like what happens to this ball rolling down. 00:07:27.630 --> 00:07:30.000 But what about negative charges? 00:07:30.000 --> 00:07:32.040 Well, negative charges will be exactly the opposite. 00:07:32.040 --> 00:07:35.040 They will get attracted by this positive charge. 00:07:35.040 --> 00:07:38.640 So they will gain kinetic energy this way. 00:07:38.640 --> 00:07:41.040 And for negative charges, it's the exact opposite 00:07:41.040 --> 00:07:43.500 as they go from here to here, this is a direction 00:07:43.500 --> 00:07:45.870 in which they are losing potential energy 00:07:45.870 --> 00:07:47.460 and gaining kinetic energy. 00:07:47.460 --> 00:07:49.140 So this must be high, this must be low, 00:07:49.140 --> 00:07:51.420 this should represent the direction of the downhill. 00:07:51.420 --> 00:07:53.880 But now the problem is which direction should we say 00:07:53.880 --> 00:07:56.340 is down for the charges? 00:07:56.340 --> 00:07:58.680 Well, we could say, hey, for positive charge, this is down 00:07:58.680 --> 00:08:00.870 and say negative charges, this is the down, 00:08:00.870 --> 00:08:03.210 but we decided no, no, no, let's just use one of these 00:08:03.210 --> 00:08:06.120 as our reference and we'll just consider one direction 00:08:06.120 --> 00:08:07.590 as our actual down. 00:08:07.590 --> 00:08:09.510 So we decided, hey, whatever happens 00:08:09.510 --> 00:08:11.580 for a positive charge, let's use positive charge 00:08:11.580 --> 00:08:12.450 as our reference, 00:08:12.450 --> 00:08:14.850 and whichever direction positive charge natural tends 00:08:14.850 --> 00:08:17.460 to go, we'll call that direction as our down 00:08:17.460 --> 00:08:19.860 for charges, right, down in potential. 00:08:19.860 --> 00:08:21.690 Because of that reference, 00:08:21.690 --> 00:08:24.120 by definition, positive charges go 00:08:24.120 --> 00:08:25.950 down the electric potential. 00:08:25.950 --> 00:08:27.990 Negative charges look end up going 00:08:27.990 --> 00:08:29.501 up the electric potential, not 00:08:29.501 --> 00:08:31.140 because they're literally going 00:08:31.140 --> 00:08:32.850 to a higher potential energy region. 00:08:32.850 --> 00:08:34.110 No, no, they're also going towards 00:08:34.110 --> 00:08:35.340 lower potential energy region. 00:08:35.340 --> 00:08:37.980 It's just a reference because our reference point for high 00:08:37.980 --> 00:08:40.353 and low is chosen, you know, from the perspective 00:08:40.353 --> 00:08:41.850 of a positive charge. 00:08:41.850 --> 00:08:43.200 Because of that reference, 00:08:43.200 --> 00:08:46.200 negative charges end up going up the potential, 00:08:46.200 --> 00:08:48.330 they have a natural tendency to go up the potential. 00:08:48.330 --> 00:08:49.170 Does that make sense? 00:08:49.170 --> 00:08:51.150 And therefore, electrons, which are negative charges, 00:08:51.150 --> 00:08:54.990 have a natural tendency to go up the electric potential. 00:08:54.990 --> 00:08:56.580 Now, the final question we could have is 00:08:56.580 --> 00:08:57.660 the direction of the current. 00:08:57.660 --> 00:08:59.790 What is the direction of the current over here? 00:08:59.790 --> 00:09:01.230 Well, we could say, hey, 00:09:01.230 --> 00:09:02.938 whichever direction the charges are drifting, well 00:09:02.938 --> 00:09:04.920 that itself could be the direction of the current. 00:09:04.920 --> 00:09:06.630 That's the most natural way to think about it, right? 00:09:06.630 --> 00:09:07.920 So electrons are drifting this way. 00:09:07.920 --> 00:09:10.110 So let's say that that is the current, 00:09:10.110 --> 00:09:11.040 but again, there's a problem 00:09:11.040 --> 00:09:12.840 because we have positive and negative charges. 00:09:12.840 --> 00:09:16.080 Remember that example where we had both positive 00:09:16.080 --> 00:09:17.190 and negative charge, equal positive 00:09:17.190 --> 00:09:18.023 and negative charges flowing 00:09:18.023 --> 00:09:19.650 through an area giving me zero current 00:09:19.650 --> 00:09:21.900 because a net charge over here is zero. 00:09:21.900 --> 00:09:23.760 Well, if I said that, hey, you know, 00:09:23.760 --> 00:09:25.620 whichever direction charges are moving, let's just call 00:09:25.620 --> 00:09:27.990 that direction as the current, then I have a problem. 00:09:27.990 --> 00:09:29.749 Because I could say that hey, positive charges is giving me 00:09:29.749 --> 00:09:32.130 a current this way, negative charges 00:09:32.130 --> 00:09:34.050 also giving me a current this way, 00:09:34.050 --> 00:09:36.480 but I know the total current must be zero. 00:09:36.480 --> 00:09:38.790 So that doesn't work because you know these two, 00:09:38.790 --> 00:09:41.250 if I add up, I don't get zero, I should get a net current 00:09:41.250 --> 00:09:42.390 to the right, but that's not true. 00:09:42.390 --> 00:09:44.430 I know that the current should be zero. 00:09:44.430 --> 00:09:47.430 Again, to solve for that, we decided, hey, you know what? 00:09:47.430 --> 00:09:50.100 Whichever direction, positive charges are moving, we'll say 00:09:50.100 --> 00:09:52.080 that is the direction of the current. 00:09:52.080 --> 00:09:53.910 And for the negative charges, 00:09:53.910 --> 00:09:56.040 we'll say the opposite is the direction of the current. 00:09:56.040 --> 00:09:59.130 So we said if the negative charges are moving to the right, 00:09:59.130 --> 00:10:02.640 we will say the direction of the current is to the left. 00:10:02.640 --> 00:10:06.360 And now look, now the total current becomes zero 00:10:06.360 --> 00:10:09.570 because your right and left current cancels out. 00:10:09.570 --> 00:10:10.830 Now it makes sense. 00:10:10.830 --> 00:10:12.330 So the convention 00:10:12.330 --> 00:10:14.520 for choosing the direction of the current 00:10:14.520 --> 00:10:17.070 is whichever direction positive charges are going, 00:10:17.070 --> 00:10:19.050 that is the direction of the current. 00:10:19.050 --> 00:10:21.300 If you have negative charges, opposite. 00:10:21.300 --> 00:10:23.490 Whichever direction negative charges are going, opposite to 00:10:23.490 --> 00:10:25.530 that, that will be the direction of the current. 00:10:25.530 --> 00:10:26.520 Okay? (chuckles) 00:10:26.520 --> 00:10:29.670 Now, because in wires, it's the electrons 00:10:29.670 --> 00:10:32.160 that are always drifting, that's those are the one 00:10:32.160 --> 00:10:33.420 that constitutes the current 00:10:33.420 --> 00:10:36.810 and the electrons are negatively charged particles. 00:10:36.810 --> 00:10:39.930 Our convention for the current would be not the direction 00:10:39.930 --> 00:10:42.030 of the electron flow, but in the opposite direction 00:10:42.030 --> 00:10:44.760 of the electron flow, it would be this way. 00:10:44.760 --> 00:10:47.970 So the conventional direction of the current, notice, is 00:10:47.970 --> 00:10:51.120 in the opposite direction of the electron flow. 00:10:51.120 --> 00:10:53.340 And I'll tell you what can be frustrating 00:10:53.340 --> 00:10:57.150 because in most cases we'll be dealing with electron flows. 00:10:57.150 --> 00:10:58.230 This will be frustrating because 00:10:58.230 --> 00:11:00.480 in most cases our conventional current will be 00:11:00.480 --> 00:11:03.090 in the opposite direction of the actual motion 00:11:03.090 --> 00:11:05.760 of the charges, actual drifting motion of the charges. 00:11:05.760 --> 00:11:07.933 But it's unfortunate that electrons, 00:11:07.933 --> 00:11:09.391 which are the major charge carriers 00:11:09.391 --> 00:11:11.730 in most of the circuits, end up being (chuckles) 00:11:11.730 --> 00:11:13.500 a negatively charged particle. 00:11:13.500 --> 00:11:15.630 And our positive charges are reference for us. 00:11:15.630 --> 00:11:18.390 And so it might slightly feel awkward initially, 00:11:18.390 --> 00:11:20.850 but you'll get used to it, don't worry too much. 00:11:20.850 --> 00:11:22.620 This now finally brings us to lightning. 00:11:22.620 --> 00:11:24.180 What exactly is lightning? 00:11:24.180 --> 00:11:26.190 Well, lightning is also an electric current, 00:11:26.190 --> 00:11:28.500 meaning flow of charges. 00:11:28.500 --> 00:11:30.210 But how does it happen? 00:11:30.210 --> 00:11:33.030 And more importantly, lightning is a flow 00:11:33.030 --> 00:11:35.730 of charges through air, but air is an insulator. 00:11:35.730 --> 00:11:38.160 And we saw that insulators do not conduct electricity. 00:11:38.160 --> 00:11:39.570 So what's going on over here? 00:11:39.570 --> 00:11:40.980 Well, we'll not give you too much details, 00:11:40.980 --> 00:11:45.000 but it turns out that clouds usually have charges separated. 00:11:45.000 --> 00:11:47.430 The top of it is usually positively charged 00:11:47.430 --> 00:11:50.250 and the bottom is negatively charged. 00:11:50.250 --> 00:11:52.130 Now because the bottom is closer 00:11:52.130 --> 00:11:55.440 to the earth, the negative charges push electrons 00:11:55.440 --> 00:11:58.410 of the earth away from it 'cause negative repel. 00:11:58.410 --> 00:12:02.100 And as the electrons get repelled away, the surface 00:12:02.100 --> 00:12:06.540 of the ground will be mostly positively charged. 00:12:06.540 --> 00:12:09.840 Now during a thunderstorm, the charges builds up 00:12:09.840 --> 00:12:11.610 because the air is an insulator, 00:12:11.610 --> 00:12:12.930 because there's no corona over here, 00:12:12.930 --> 00:12:14.850 the charges can build up, and as a result, 00:12:14.850 --> 00:12:17.790 the potential difference become incredibly high. 00:12:17.790 --> 00:12:20.370 It can reach millions of moist. 00:12:20.370 --> 00:12:24.780 Now, eventually what happens is that the electrons 00:12:24.780 --> 00:12:28.500 from the atoms of the air molecules, like oxygen, nitrogen, 00:12:28.500 --> 00:12:32.010 and all of those stuff can actually get ripped apart. 00:12:32.010 --> 00:12:34.050 And we'll not get into again the details of how 00:12:34.050 --> 00:12:36.060 that happens, but you can now imagine, 00:12:36.060 --> 00:12:38.400 if electrons start getting ripped apart. 00:12:38.400 --> 00:12:41.370 Now we start having charges. 00:12:41.370 --> 00:12:42.811 Once we have charged particles 00:12:42.811 --> 00:12:45.780 in between, we have a conducting channel. 00:12:45.780 --> 00:12:47.730 And once we have that conducting channel, 00:12:47.730 --> 00:12:51.030 the charges can sort of get dumped into the earth. 00:12:51.030 --> 00:12:53.730 And that's basically what we call a lightning. 00:12:53.730 --> 00:12:55.800 Now this lightning produces a lot of heat. 00:12:55.800 --> 00:12:58.740 That's one of the reason it glows and you can see it. 00:12:58.740 --> 00:13:01.020 But that heat also causes rapid expansions 00:13:01.020 --> 00:13:03.810 in the air, making the air vibrate. 00:13:03.810 --> 00:13:06.390 And these vibrations eventually reach our ears 00:13:06.390 --> 00:13:10.800 after some time, and we call that as thunder. 00:13:10.800 --> 00:13:14.550 So look, lightning is an electric current, and guess what? 00:13:14.550 --> 00:13:17.100 Sparking that happens sometimes, those annoying sparks 00:13:17.100 --> 00:13:18.630 we get whenever we get charged up 00:13:18.630 --> 00:13:20.850 and we're trying to reach out to a doorknob, for example. 00:13:20.850 --> 00:13:21.683 (laughs) 00:13:21.683 --> 00:13:23.430 It's very similar to what happens in a lightning. 00:13:23.430 --> 00:13:26.313 It's a miniature version of lightning.