# Tag Info

40

TL;DR: Air in lightning gets hot. Hot things (like the Sun) emit light in a broad spectrum; including visible. You are right there will be emissions outside the visible - but your eye doesn't pick that up. So the flash looks blue-ish white to the human eye. More complete answer: The light you see is the result of the air getting very, very hot. And just ...

38

Hank Green is describing the concept of the Planck temperature, $$T_\mathrm{P} = \sqrt{\frac{\hbar c^5}{Gk_B^2}}\approx1.4\times 10^{32}\:\mathrm K,$$ which is defined as $\frac{1}{k_B}$ times the Planck energy $E_\mathrm{P}=\sqrt{\hbar c^5/G}\approx 1.9\times 10^{9}\:\mathrm J$. As with all the Planck units, we don't really know what happens at those ...

38

The amount of heat generated by current flowing through a resistor (whether from lightning or more ordinary sources) is directly related to the power dissipated by the resistor, which is $$P = I^2 R.$$ $R$ is small for objects made from good conductors, which many metals are, and large for objects that are made from bad conductors like plastic or wood. ...

36

This is due to the principle of dielectric breakdown. During thunderstorms, the air between the cloud and the ground acts like a capacitor. When the electric field is high enough, the air partially ionizes, at which point there are free electrons to carry current and the air becomes, essentially, conductive.

34

Yes, it's possible. Though, I'm sure the engineers of the Sears Tower took that into account. Catastrophic failure of the rod is pretty straightforward. Lighting is a ton of electrical current, and the rod has some resistance. Current through a resistance makes heat by Joule heating, which says that the power is proportional to the resistance times the ...

33

You are mixing up two different things. The observers know that light takes time to travel the distance from the strike to their eyes. So when they are calculating the time the strike occurs they allow for the travel time. Since both your observers make allowances for the light travel time they will both agree on the time the strikes occurred. What special ...

25

This is an interesting question. Unfortunately, the answer is probably no for two reasons. There is a nice way of telling how far away a lightning strike was by counting the seconds before the thunder reaches you though. First let me tell you why your method probably won't work, then I'll tell you how to calculate the distance based on the time of arrival ...

25

They exist, they're just rarer, which is why you don't often see them. They're called gigantic jets, and they connect storm clouds to the reservoir of charge in the ionosphere. Here's one that was photographed during Tropical Storm Cristobal in 2008 (source: https://www.livescience.com/10572-gigantic-lightning-jets-shoot-clouds-space.html): Unfortunately, ...

23

I'm not an expert, but I spent some time with references 1 and 2 several years ago. This answer is based on some notes I took. Measurements using the radio waves produced by lightning indicate that lightning bolts inside thunderclouds (the ones that we can't see directly) are often mostly horizontal, and they can be anywhere from 1/2 km in length to 20 km in ...

19

Your assumptions are right. There is indeed physics involved in lightning shapes. Why can’t lightning just be in a plain, straight shape? From the Indiana Public Media's Moment of Science Podcast episode "The Shape of Lightning Bolts": The answer has to do with the complex way a lightning bolt forms. Although it looks like it forms all at once, a ...

18

As already stated by John Rennie, the observers are already aware of the property that light travels at a constant speed, and they account for the given fact, so even if the lightning strikes are not simultaneous for them, they know that because of the fact that light travels at a constant speed. But for any two observers moving relative to each other, even ...

16

I think yes, you can get some distance information from analyzing the thunder sound. I am basing this mostly on having personally heard many thunderclaps, both far and near, of reasonably known distance to the lightning. Anyone that has ever experienced a near (100 m or less) thunderclap can tell you it sounds a lot more "sharp" than a distant one, not to ...

14

From How Big Is A Lightning Bolt? we see that a lightining bolt is “an inch wide and five miles long”, and at “50,000 °F”. So in useful units, approximately 3 cm diameter, 8 kilometer long, 28000 K hot. If we consider that the heat is mostly due to black body radiation (for a perfect black body with an emissivity of $\epsilon = 1$), then the power will be ...

13

The lightning rod is based on two principles theorized by Benjamin Franklin. Lightning dissipation theory, and lightning diversion theory. Lightning Dissipation Theory This theory says that if you point a pointy metal object toward a polarized cloud, the metal object will be able to bleed off some of the energy from the cloud. Thus preventing a lightning ...

13

Air does not conduct electricity in the way that metals do. We normally think of conductors as metals with free electrons that move easily throughout the whole metal. Small voltages move the electrons and a current can flow. In the case of air and many other materials there are electrons present, but they are firmly bound to individual atoms and molecules ...

13

Suppose there is a charged cloud floating over your conductor. Then making your lightning conductor pointy at the edge would facilitate better discharge by setting up a high electric field. We will take a spherical approximation of the pointed end, then ${\sigma}=\frac{q}{4\pi r^2}$ is the surface charge density of the end. It has a very high surface ...

12

The National Weather Serivce has a page on ways someone can get struck by lightning. Two possibilities jump out at me as potential killers in the case of the reindeer: 1. Ground current Lightning might hit a tall object - a tree, telephone pole, or something else - and travel through it into the ground. After this, it may spread out in various directions ...

11

The high electrical current in a lightning strike delivers heat energy along the full length of the lightning bolt. Part of that length is in the ionized air over the plane, part is the plane's fuselage, and part is the ionized air from the plane down to ground. The current is the same, but the heat generated is proportional to the electrical resistance ...

11

Yes. A lightning conductor on top of a high-rise structure is designed to minimize the possibility of lightning hitting the structure by the virtue of its pointed tip giving rise to very high electric fields (the reason). However this doesn't always ensure that lightning will definitely strike the conductor. This link has quite a few examples of the same. ...

10

A very interesting question, especially because of the discussion that it spawned. All the answers here seem to revolve about two different mechanisms: thermal radiation of the 50.000K plasma radiation due to recombination of the resulting plasma It's not very easy to find authorative sources on either, but googling for "spectrum of lightning" turned up ...

10

Why is it never just a straight line? I think it can be interesting to answer both questions and add a few interesting details to the answer already given. Electrons move in a straight line only in vacuum, where they meet no obstacles. What happens here is the same that happens with a river: the water of a waterfall goes in a straight line because it ...

10

The point of the point is to increase the electric field near the point. Small radius curves will have a higher local electric field, eventually creating a localize area where the field is greater than the dielectric strength of the air. This results in what I refer to as "micro-lightning." This microlightning discharges the air (or cloud) before the ...

10

I know this is a little more than you asked for, but lightning is very interesting. A lightning event is usually called a flash and lasts about 0.5 seconds. It consists of a near-invisible stepped leader followed by a very bright return stroke backwards along the path of the stepped leader. Following the first stroke, there may be additional strokes in the ...

9

This entry that describes the build up of charge is contradictory to the statement you post, free electrons do not escape to the air but go down in the ground leaving positive charges . In the end, a storm cloud becomes polarized with positive charges carried to the upper portions of the clouds and negative portions gravitating towards the bottom of the ...

9

At sufficiently high voltages almost everything conducts due in part to quantum tunneling of electrons. An insulator has a breakdown voltage which is the field strength required before it will start conducting. Related to the breakdown voltage is the dielectric strength which is the minimum voltage over distance ($\mathrm{V}/\mathrm{m}$) before a material ...

9

If you look at slow-motion videos of lightning strikes you'll notice that a "pilot lightning", called a step leader, originates indeed in the cloud and propagates, branching out roughly radially from its point of origin. The general direction is certainly dictated by the gradient of the electric field while the chaotic element is introduced by the ...

8

A few things I can think of straight away: Power line pylons are usually the tallest objects in the countryside. They are giant grounded metal objects. As lightning wants to move along the path of least resistance, they are preferred over other objects. Power lines also usually have one or two grounded wires on top, which act as lightning rods which protect ...

7

Air is not a dispersive medium for sound waves. At least, in normal condition. When a lightning is produced, the air is heated up to a very high temperature, creating a shock wave like. The sound heard depends on the position of the observer, far way or near the thunder origin, and the shape and direction of the thunderbolt. Lightning can be cloud to cloud ...

6

I presume you did not see the flash, so cannot use that as a timing mark. From Wikipedia "The dependence on frequency and pressure are normally insignificant in practical applications. In dry air, the speed of sound increases by about 0.1 m/s as the frequency rises from 10 Hz to 100 Hz. For audible frequencies above 100 Hz it is relatively constant. " You ...

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