0:00:00.300,0:00:01.500 - [Lecturer] Electricity that lights up 0:00:01.500,0:00:05.460 above looks very different[br]than lightning strikes, 0:00:05.460,0:00:08.070 but they're actually more[br]similar than one might think 0:00:08.070,0:00:10.470 because they both have electric current. 0:00:10.470,0:00:12.450 So let's understand what[br]electric current is, 0:00:12.450,0:00:13.800 how they're produced, 0:00:13.800,0:00:16.110 and also get to understand a[br]little bit about lightning. 0:00:16.110,0:00:18.120 So what exactly is electric current? 0:00:18.120,0:00:19.140 Well think of electric current 0:00:19.140,0:00:23.190 as a flow of net charge[br]through any given area. 0:00:23.190,0:00:26.520 Here's what I mean by flow of net charge. 0:00:26.520,0:00:28.770 Well imagine you have a[br]tiny cross-sectional area 0:00:28.770,0:00:30.480 through which you have equal amount 0:00:30.480,0:00:31.440 of positive charges flowing 0:00:31.440,0:00:33.870 to the right and left in any given time. 0:00:33.870,0:00:35.430 Now notice there is a flow, 0:00:35.430,0:00:37.260 but there is no net flow (chuckles) 0:00:37.260,0:00:39.990 and therefore here we say[br]there is zero current. 0:00:39.990,0:00:42.900 Another interesting example is[br]what if you have equal amount 0:00:42.900,0:00:45.060 of positive and negative charges flowing 0:00:45.060,0:00:47.430 in the same direction in[br]the same time, let's say 0:00:47.430,0:00:49.680 through again, a given[br]cross-sectional area. 0:00:49.680,0:00:51.840 Again, notice there is a flow of charges, 0:00:51.840,0:00:54.510 but the total flow over here, total charge 0:00:54.510,0:00:55.980 that's flowing is zero. (chuckles) 0:00:55.980,0:00:57.870 So net charge is still zero 0:00:57.870,0:01:00.510 and therefore there is no[br]electric current over here. 0:01:00.510,0:01:05.070 Okay, what about now? Ooh, now[br]we do have electric current. 0:01:05.070,0:01:08.610 Now we have a net positive[br]charge flowing to the right. 0:01:08.610,0:01:10.170 Over here there is an electric current. 0:01:10.170,0:01:13.800 Now we do have a net negative[br]charges flowing to the right. 0:01:13.800,0:01:16.560 We do have an electric current. Okay? 0:01:16.560,0:01:20.940 So it's a flow of net charge,[br]but how do you measure it? 0:01:20.940,0:01:24.540 Well, we measure it as the[br]amount of charges flowing 0:01:24.540,0:01:27.900 through any given[br]cross-sectional area per second. 0:01:27.900,0:01:31.170 So you can think of it[br]as coulomb per second. 0:01:31.170,0:01:35.160 How many coulombs are flowing per second? 0:01:35.160,0:01:37.593 And the coulombs per[br]second is also called, 0:01:38.580,0:01:43.580 it's also called Amperes,[br]okay? Capital A, Amperes. 0:01:43.620,0:01:45.390 And just to give you typical numbers, 0:01:45.390,0:01:47.670 your air conditioners heaters, 0:01:47.670,0:01:50.580 they drop out 10 to 15 Amperes of current. 0:01:50.580,0:01:54.330 Your ceiling fan tube lights,[br]television sets less than 0:01:54.330,0:01:56.130 that, about one or two amps. 0:01:56.130,0:01:59.250 And your smaller circuits[br]like you know the toy circuits 0:01:59.250,0:02:01.470 and stuff, they would be even lesser. 0:02:01.470,0:02:04.404 It would be fraction of Amperes.[br]But what about lightning? 0:02:04.404,0:02:05.460 Ooh. (chuckles) 0:02:05.460,0:02:09.270 Lightning can have tens of[br]thousands of Amperes in them. 0:02:09.270,0:02:11.100 Okay, how do we set up[br]an electric current? 0:02:11.100,0:02:12.450 How do we get an electric current? 0:02:12.450,0:02:16.380 Well, for an electric[br]current we need a voltage. 0:02:16.380,0:02:18.600 Just like how, if you need[br]to make a ball roll, you need 0:02:18.600,0:02:20.910 to have a height difference, 0:02:20.910,0:02:24.330 which produces a gravitational[br]potential difference 0:02:24.330,0:02:26.100 across the end of say a plank. 0:02:26.100,0:02:30.030 Similarly, if you need to set[br]up a current through a wire, 0:02:30.030,0:02:34.110 you need to have an electric[br]potential difference 0:02:34.110,0:02:35.490 across the ends of it. 0:02:35.490,0:02:37.170 When you have an electric[br]potential difference, 0:02:37.170,0:02:39.720 you can get a current, but[br]you also need to make sure 0:02:39.720,0:02:41.700 that there are some charges. 0:02:41.700,0:02:45.150 There are charges that are[br]free to move in your material. 0:02:45.150,0:02:49.050 Not all materials have that,[br]for example, glass or plastic. 0:02:49.050,0:02:50.670 Well, they don't have free charges because 0:02:50.670,0:02:52.860 if you look inside them,[br]well you can model them 0:02:52.860,0:02:54.060 and say that you know what? 0:02:54.060,0:02:57.330 The electrons inside these[br]atoms are very tightly bound. 0:02:57.330,0:02:59.160 So there are no free electrons to move. 0:02:59.160,0:03:00.450 There are no charges to move. 0:03:00.450,0:03:01.283 So if you put a voltage 0:03:01.283,0:03:04.230 across them, you'll probably[br]get no current over here. 0:03:04.230,0:03:07.020 We call such material insulators, glass, 0:03:07.020,0:03:10.920 wood, plastic, these are[br]examples of insulators. 0:03:10.920,0:03:12.510 On the other hand, if you take metals 0:03:12.510,0:03:14.850 of which wires are made[br]of, then you'll find 0:03:14.850,0:03:18.120 that the outermost electrons[br]are not tightly bound. 0:03:18.120,0:03:21.960 As a result, they are free[br]to move around the material. 0:03:21.960,0:03:23.640 We call them free electrons. 0:03:23.640,0:03:25.950 And since you have free charges available 0:03:25.950,0:03:28.218 for motion, we call these[br]materials conductors 0:03:28.218,0:03:30.540 because if you put a voltage across them, 0:03:30.540,0:03:34.260 well these electrons can move[br]and contribute to current. 0:03:34.260,0:03:37.350 So you need a voltage[br]across a conducting medium 0:03:37.350,0:03:39.930 for electric current. 0:03:39.930,0:03:42.750 Okay, but how do you get a[br]voltage in the first place? 0:03:42.750,0:03:45.053 Well, in small circuits,[br]you probably already know, 0:03:45.053,0:03:47.310 voltage is given by a battery. 0:03:47.310,0:03:49.440 One end of the battery[br]is at a higher potential, 0:03:49.440,0:03:51.247 another end of the battery[br]is at lower potential. 0:03:51.247,0:03:53.850 And when you connect it[br]to a circuit, it provides 0:03:53.850,0:03:54.960 the potential difference. 0:03:54.960,0:03:57.480 But in larger circuits for[br]like for example, the circuits 0:03:57.480,0:04:00.330 in our houses, well the[br]potential difference is provided 0:04:00.330,0:04:03.870 by large electric generators[br]in our power stations. 0:04:03.870,0:04:06.870 And by the way, while drawing[br]a battery in our circuit, 0:04:06.870,0:04:09.120 well we use a circuit[br]symbol that looks like this. 0:04:09.120,0:04:12.480 The longer line represents[br]the positive terminal 0:04:12.480,0:04:15.360 and the shorter thick line[br]represents a negative terminal. 0:04:15.360,0:04:16.920 So that if you just draw[br]this, we don't have to draw 0:04:16.920,0:04:18.870 like a big battery over here. 0:04:18.870,0:04:20.460 Anyways, even though we have a battery 0:04:20.460,0:04:23.100 in this circuit right now,[br]we don't have a current, 0:04:23.100,0:04:25.710 we don't have a potential[br]difference across this bulb. 0:04:25.710,0:04:26.580 Why? 0:04:26.580,0:04:27.900 Well, you can see over here, that's 0:04:27.900,0:04:30.390 because the circuit is not closed. 0:04:30.390,0:04:32.970 We say because there[br]is some air in between. 0:04:32.970,0:04:35.520 Air is an excellent insulator and 0:04:35.520,0:04:38.130 therefore there's not going[br]to be any current over here. 0:04:38.130,0:04:40.020 In order for there to[br]be a current, we need 0:04:40.020,0:04:43.410 to close the circuit, meaning[br]we need to connect this gap 0:04:43.410,0:04:45.930 and that's where the switch[br]is, this is a switch. 0:04:45.930,0:04:48.630 So if I close the switch 0:04:48.630,0:04:52.770 like this, now the circuit is complete. 0:04:52.770,0:04:55.320 Now there'll be a potential[br]difference across the ends 0:04:55.320,0:04:58.500 of the ball when now there'll[br]be a current over here. 0:04:58.500,0:05:00.000 I'm gonna open the switch. 0:05:00.000,0:05:02.250 There is no electric current,[br]the circuit is broken. 0:05:02.250,0:05:04.950 Close the switch, there's going[br]to be an electric current. 0:05:04.950,0:05:06.690 Now because I compared charges moving 0:05:06.690,0:05:08.880 through a ball rolling[br]down, we might model it 0:05:08.880,0:05:12.300 by thinking that hey,[br]when there is no voltage, 0:05:12.300,0:05:14.100 all the charges are at[br]rest, say the electrons 0:05:14.100,0:05:16.705 over here are at rest and when[br]I do complete the circuit, 0:05:16.705,0:05:18.780 the electrons are now nicely moving. 0:05:18.780,0:05:20.910 But that's not a very accurate[br]way to think about it, 0:05:20.910,0:05:22.050 that's not a good model. 0:05:22.050,0:05:23.970 Instead, a better model[br]is if you were to peek 0:05:23.970,0:05:26.610 inside the wire, we[br]find that the electrons 0:05:26.610,0:05:28.200 are randomly moving, bumping 0:05:28.200,0:05:29.910 into stuff because they have a lot 0:05:29.910,0:05:32.880 of energy even when there is no voltage. 0:05:32.880,0:05:34.470 So they're not at rest, they're 0:05:34.470,0:05:36.960 in fact moving at very high speeds. 0:05:36.960,0:05:38.760 But what happens when we close the switch? 0:05:38.760,0:05:40.740 When we close the circuit, look, 0:05:40.740,0:05:42.270 there is a potential difference 0:05:42.270,0:05:45.240 and therefore there is an[br]electric field setup in the wire 0:05:45.240,0:05:47.640 that electric field starts[br]pushing on the electrons. 0:05:47.640,0:05:49.080 And look, you can now see the electrons 0:05:49.080,0:05:51.720 are slowly drifting to the left. 0:05:51.720,0:05:56.250 It's that drifting motion[br]that constitutes the current 0:05:56.250,0:05:58.380 and what causes them to drift to the left? 0:05:58.380,0:06:00.030 Again, there are some analogies which says 0:06:00.030,0:06:02.820 that electrons push on each[br]other making them drift. 0:06:02.820,0:06:05.130 But that's again not very accurate. 0:06:05.130,0:06:06.660 A better way to think about it is 0:06:06.660,0:06:08.790 that the battery produces[br]the electric field. 0:06:08.790,0:06:10.590 There's an electric field[br]set up inside the wire. 0:06:10.590,0:06:14.160 It's that electric field that is causing, 0:06:14.160,0:06:16.380 that's pushing the[br]electrons, making them drift 0:06:16.380,0:06:17.850 to the left over here. 0:06:17.850,0:06:19.260 But wait a second, why did I show 0:06:19.260,0:06:22.380 that the electrons are[br]drifting to the left over here? 0:06:22.380,0:06:23.760 Let's think about it. 0:06:23.760,0:06:25.350 So one way to think[br]about it's, you could say 0:06:25.350,0:06:26.670 that hey, electrons are being attracted 0:06:26.670,0:06:29.490 by the positive terminal of[br]the battery being repelled 0:06:29.490,0:06:31.470 by the negative terminal[br]of the battery, making 0:06:31.470,0:06:33.150 the electrons go this way. 0:06:33.150,0:06:34.710 But a question that could raise is, 0:06:34.710,0:06:36.750 in the wire that means[br]the electrons are going 0:06:36.750,0:06:39.510 from a lower potential[br]to a higher potential 0:06:39.510,0:06:40.530 like going uphill. 0:06:40.530,0:06:41.820 How does that make any sense? 0:06:41.820,0:06:43.920 That was a point of[br]confusion for a long time. 0:06:43.920,0:06:46.380 So let's talk about it a little bit. Okay? 0:06:46.380,0:06:48.270 If I have a big positive charge 0:06:48.270,0:06:52.050 and next to it I keep a[br]very tiny positive charge 0:06:52.050,0:06:53.640 and at rest, let's say, 0:06:53.640,0:06:56.220 and I let go of it, then[br]we know it gets repelled 0:06:56.220,0:06:59.070 and it gains kinetic[br]energy in this direction. 0:06:59.070,0:07:01.140 Now because energy is conserved,[br]we could ask where did 0:07:01.140,0:07:02.490 that kinetic energy come from? 0:07:02.490,0:07:06.300 We say, ah, there it must have[br]come from potential energy. 0:07:06.300,0:07:07.860 So as it goes from here to here, 0:07:07.860,0:07:10.410 the system must lose potential energy 0:07:10.410,0:07:12.060 and therefore we can now say that hey, 0:07:12.060,0:07:14.940 this point represents[br]high potential region. 0:07:14.940,0:07:17.490 This point represents low potential region 0:07:17.490,0:07:21.510 and this represents the downhill[br]direction for the charges. 0:07:21.510,0:07:23.280 As you go from here to[br]here, it's potential energy 0:07:23.280,0:07:24.930 starts getting converted[br]into kinetic energy. 0:07:24.930,0:07:27.630 Kind of like what happens[br]to this ball rolling down. 0:07:27.630,0:07:30.000 But what about negative charges? 0:07:30.000,0:07:32.040 Well, negative charges will[br]be exactly the opposite. 0:07:32.040,0:07:35.040 They will get attracted[br]by this positive charge. 0:07:35.040,0:07:38.640 So they will gain kinetic energy this way. 0:07:38.640,0:07:41.040 And for negative charges,[br]it's the exact opposite 0:07:41.040,0:07:43.500 as they go from here to[br]here, this is a direction 0:07:43.500,0:07:45.870 in which they are losing potential energy 0:07:45.870,0:07:47.460 and gaining kinetic energy. 0:07:47.460,0:07:49.140 So this must be high, this must be low, 0:07:49.140,0:07:51.420 this should represent the[br]direction of the downhill. 0:07:51.420,0:07:53.880 But now the problem is which[br]direction should we say 0:07:53.880,0:07:56.340 is down for the charges? 0:07:56.340,0:07:58.680 Well, we could say, hey, for[br]positive charge, this is down 0:07:58.680,0:08:00.870 and say negative charges,[br]this is the down, 0:08:00.870,0:08:03.210 but we decided no, no, no,[br]let's just use one of these 0:08:03.210,0:08:06.120 as our reference and we'll[br]just consider one direction 0:08:06.120,0:08:07.590 as our actual down. 0:08:07.590,0:08:09.510 So we decided, hey, whatever happens 0:08:09.510,0:08:11.580 for a positive charge,[br]let's use positive charge 0:08:11.580,0:08:12.450 as our reference, 0:08:12.450,0:08:14.850 and whichever direction[br]positive charge natural tends 0:08:14.850,0:08:17.460 to go, we'll call that[br]direction as our down 0:08:17.460,0:08:19.860 for charges, right, down in potential. 0:08:19.860,0:08:21.690 Because of that reference, 0:08:21.690,0:08:24.120 by definition, positive charges go 0:08:24.120,0:08:25.950 down the electric potential. 0:08:25.950,0:08:27.990 Negative charges look end up going 0:08:27.990,0:08:29.501 up the electric potential, not 0:08:29.501,0:08:31.140 because they're literally going 0:08:31.140,0:08:32.850 to a higher potential energy region. 0:08:32.850,0:08:34.110 No, no, they're also going towards 0:08:34.110,0:08:35.340 lower potential energy region. 0:08:35.340,0:08:37.980 It's just a reference because[br]our reference point for high 0:08:37.980,0:08:40.353 and low is chosen, you[br]know, from the perspective 0:08:40.353,0:08:41.850 of a positive charge. 0:08:41.850,0:08:43.200 Because of that reference, 0:08:43.200,0:08:46.200 negative charges end up[br]going up the potential, 0:08:46.200,0:08:48.330 they have a natural tendency[br]to go up the potential. 0:08:48.330,0:08:49.170 Does that make sense? 0:08:49.170,0:08:51.150 And therefore, electrons,[br]which are negative charges, 0:08:51.150,0:08:54.990 have a natural tendency to[br]go up the electric potential. 0:08:54.990,0:08:56.580 Now, the final question we could have is 0:08:56.580,0:08:57.660 the direction of the current. 0:08:57.660,0:08:59.790 What is the direction of[br]the current over here? 0:08:59.790,0:09:01.230 Well, we could say, hey, 0:09:01.230,0:09:02.938 whichever direction the[br]charges are drifting, well 0:09:02.938,0:09:04.920 that itself could be the[br]direction of the current. 0:09:04.920,0:09:06.630 That's the most natural way[br]to think about it, right? 0:09:06.630,0:09:07.920 So electrons are drifting this way. 0:09:07.920,0:09:10.110 So let's say that that is the current, 0:09:10.110,0:09:11.040 but again, there's a problem 0:09:11.040,0:09:12.840 because we have positive[br]and negative charges. 0:09:12.840,0:09:16.080 Remember that example[br]where we had both positive 0:09:16.080,0:09:17.190 and negative charge, equal positive 0:09:17.190,0:09:18.023 and negative charges flowing 0:09:18.023,0:09:19.650 through an area giving me zero current 0:09:19.650,0:09:21.900 because a net charge over here is zero. 0:09:21.900,0:09:23.760 Well, if I said that, hey, you know, 0:09:23.760,0:09:25.620 whichever direction charges[br]are moving, let's just call 0:09:25.620,0:09:27.990 that direction as the current,[br]then I have a problem. 0:09:27.990,0:09:29.749 Because I could say that hey,[br]positive charges is giving me 0:09:29.749,0:09:32.130 a current this way, negative charges 0:09:32.130,0:09:34.050 also giving me a current this way, 0:09:34.050,0:09:36.480 but I know the total current must be zero. 0:09:36.480,0:09:38.790 So that doesn't work[br]because you know these two, 0:09:38.790,0:09:41.250 if I add up, I don't get zero,[br]I should get a net current 0:09:41.250,0:09:42.390 to the right, but that's not true. 0:09:42.390,0:09:44.430 I know that the current should be zero. 0:09:44.430,0:09:47.430 Again, to solve for that, we[br]decided, hey, you know what? 0:09:47.430,0:09:50.100 Whichever direction, positive[br]charges are moving, we'll say 0:09:50.100,0:09:52.080 that is the direction of the current. 0:09:52.080,0:09:53.910 And for the negative charges, 0:09:53.910,0:09:56.040 we'll say the opposite is[br]the direction of the current. 0:09:56.040,0:09:59.130 So we said if the negative[br]charges are moving to the right, 0:09:59.130,0:10:02.640 we will say the direction of[br]the current is to the left. 0:10:02.640,0:10:06.360 And now look, now the[br]total current becomes zero 0:10:06.360,0:10:09.570 because your right and[br]left current cancels out. 0:10:09.570,0:10:10.830 Now it makes sense. 0:10:10.830,0:10:12.330 So the convention 0:10:12.330,0:10:14.520 for choosing the direction of the current 0:10:14.520,0:10:17.070 is whichever direction[br]positive charges are going, 0:10:17.070,0:10:19.050 that is the direction of the current. 0:10:19.050,0:10:21.300 If you have negative charges, opposite. 0:10:21.300,0:10:23.490 Whichever direction negative[br]charges are going, opposite to 0:10:23.490,0:10:25.530 that, that will be the[br]direction of the current. 0:10:25.530,0:10:26.520 Okay? (chuckles) 0:10:26.520,0:10:29.670 Now, because in wires, it's the electrons 0:10:29.670,0:10:32.160 that are always drifting,[br]that's those are the one 0:10:32.160,0:10:33.420 that constitutes the current 0:10:33.420,0:10:36.810 and the electrons are[br]negatively charged particles. 0:10:36.810,0:10:39.930 Our convention for the current[br]would be not the direction 0:10:39.930,0:10:42.030 of the electron flow, but[br]in the opposite direction 0:10:42.030,0:10:44.760 of the electron flow,[br]it would be this way. 0:10:44.760,0:10:47.970 So the conventional direction[br]of the current, notice, is 0:10:47.970,0:10:51.120 in the opposite direction[br]of the electron flow. 0:10:51.120,0:10:53.340 And I'll tell you what can be frustrating 0:10:53.340,0:10:57.150 because in most cases we'll be[br]dealing with electron flows. 0:10:57.150,0:10:58.230 This will be frustrating because 0:10:58.230,0:11:00.480 in most cases our[br]conventional current will be 0:11:00.480,0:11:03.090 in the opposite direction[br]of the actual motion 0:11:03.090,0:11:05.760 of the charges, actual[br]drifting motion of the charges. 0:11:05.760,0:11:07.933 But it's unfortunate that electrons, 0:11:07.933,0:11:09.391 which are the major charge carriers 0:11:09.391,0:11:11.730 in most of the circuits,[br]end up being (chuckles) 0:11:11.730,0:11:13.500 a negatively charged particle. 0:11:13.500,0:11:15.630 And our positive charges[br]are reference for us. 0:11:15.630,0:11:18.390 And so it might slightly[br]feel awkward initially, 0:11:18.390,0:11:20.850 but you'll get used to[br]it, don't worry too much. 0:11:20.850,0:11:22.620 This now finally brings us to lightning. 0:11:22.620,0:11:24.180 What exactly is lightning? 0:11:24.180,0:11:26.190 Well, lightning is also[br]an electric current, 0:11:26.190,0:11:28.500 meaning flow of charges. 0:11:28.500,0:11:30.210 But how does it happen? 0:11:30.210,0:11:33.030 And more importantly, lightning is a flow 0:11:33.030,0:11:35.730 of charges through air,[br]but air is an insulator. 0:11:35.730,0:11:38.160 And we saw that insulators[br]do not conduct electricity. 0:11:38.160,0:11:39.570 So what's going on over here? 0:11:39.570,0:11:40.980 Well, we'll not give you too much details, 0:11:40.980,0:11:45.000 but it turns out that clouds[br]usually have charges separated. 0:11:45.000,0:11:47.430 The top of it is usually[br]positively charged 0:11:47.430,0:11:50.250 and the bottom is negatively charged. 0:11:50.250,0:11:52.130 Now because the bottom is closer 0:11:52.130,0:11:55.440 to the earth, the negative[br]charges push electrons 0:11:55.440,0:11:58.410 of the earth away from[br]it 'cause negative repel. 0:11:58.410,0:12:02.100 And as the electrons get[br]repelled away, the surface 0:12:02.100,0:12:06.540 of the ground will be[br]mostly positively charged. 0:12:06.540,0:12:09.840 Now during a thunderstorm,[br]the charges builds up 0:12:09.840,0:12:11.610 because the air is an insulator, 0:12:11.610,0:12:12.930 because there's no corona over here, 0:12:12.930,0:12:14.850 the charges can build up, and as a result, 0:12:14.850,0:12:17.790 the potential difference[br]become incredibly high. 0:12:17.790,0:12:20.370 It can reach millions of moist. 0:12:20.370,0:12:24.780 Now, eventually what happens[br]is that the electrons 0:12:24.780,0:12:28.500 from the atoms of the air[br]molecules, like oxygen, nitrogen, 0:12:28.500,0:12:32.010 and all of those stuff can[br]actually get ripped apart. 0:12:32.010,0:12:34.050 And we'll not get into[br]again the details of how 0:12:34.050,0:12:36.060 that happens, but you can now imagine, 0:12:36.060,0:12:38.400 if electrons start getting ripped apart. 0:12:38.400,0:12:41.370 Now we start having charges. 0:12:41.370,0:12:42.811 Once we have charged particles 0:12:42.811,0:12:45.780 in between, we have a conducting channel. 0:12:45.780,0:12:47.730 And once we have that conducting channel, 0:12:47.730,0:12:51.030 the charges can sort of[br]get dumped into the earth. 0:12:51.030,0:12:53.730 And that's basically[br]what we call a lightning. 0:12:53.730,0:12:55.800 Now this lightning produces a lot of heat. 0:12:55.800,0:12:58.740 That's one of the reason it[br]glows and you can see it. 0:12:58.740,0:13:01.020 But that heat also causes rapid expansions 0:13:01.020,0:13:03.810 in the air, making the air vibrate. 0:13:03.810,0:13:06.390 And these vibrations[br]eventually reach our ears 0:13:06.390,0:13:10.800 after some time, and we[br]call that as thunder. 0:13:10.800,0:13:14.550 So look, lightning is an[br]electric current, and guess what? 0:13:14.550,0:13:17.100 Sparking that happens[br]sometimes, those annoying sparks 0:13:17.100,0:13:18.630 we get whenever we get charged up 0:13:18.630,0:13:20.850 and we're trying to reach out[br]to a doorknob, for example. 0:13:20.850,0:13:21.683 (laughs) 0:13:21.683,0:13:23.430 It's very similar to what[br]happens in a lightning. 0:13:23.430,0:13:26.313 It's a miniature version of lightning.