# Tag Info

34

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.

31

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 ...

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 ...

23

1) yes, it basically will find a non-optimal solution. At every point, the top of the ray looks for the bigger potential gradient, the charge in the surrounding volume grows, polarizing surrounding material (air, in this case) until a bigger gradient shows up and the ray continues over that direction. This is why the lightining path looks like a jigsaw; its ...

15

In fresh water what makes lightening so dangerous to a swimmer is that most of the current travels on the surface of the water, so rather then getting a $1/r^2$ falloff in current density, you see a $1/r$ falloff. Obviously eventually it will be conducted down into the mass of the water, but this takes a many meters. In salt water, this should happen much ...

15

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 ...

13

Most probably yes; wireless devices are not grounded, so they are not lighting rods of any kind as it is frequently assumed. There are some theories that cell phones somehow attracts lightnings by the field they produce, but the theory behind is weak. Experimental evaluation is very hard, since lightning hits are quite rare, such events are guided by ...

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 ...

12

I have always assumed it could be put down to a small set of causes: The stroke may have a physical extent and geometry that leads to a perceptible duration between the arrival of the sound due to the near part of the strike and that due to the far part. That is, what Georg said. If the geometry of the terrain is right you may be hearing echos off of cliff ...

11

Yes, if it is not a plastic covered car it is an effective Faraday cage. If the tires are such that the car is insulated electrically, if it is hit it will take some time to discharge to the ground, but still the passengers would be safer than standing next to it outside. I have learned that modern tires are particularly constructed so that the static ...

10

Here's a crude way to look at the problem: Suppose there are $N$ wires. Each has resistance $R$, common potential difference $V$ and are connected in parallel. So the current through each wire is $I = \frac{V}{NR}$. Let's imagine a hypothetical wire formed by sea water which has a length, $L$ and cross sectional area, $S$. There are approximately $\frac{2\... 10 I can't point to a definitive reference, but my recollection is that thunderstorms are associated with a lower layer of warm air rising rapidly through an upper layer of cold air. It's the rapid vertical transport that generates the static charge and hence the lightening. In winter it's rare to get these atmospheric conditions. So it's not that there's ... 10 Suppose that you have an negatively charged cloud. Floating over your conductor. Then making your lightning conductor pointy at the edge, facilitates better discharge. Because the electric field set up would be high.${\sigma}=\frac{q}{4\pi r^2}$, We will take an spherical approximation of the pointed end. It will have a very small radius thus high surface ... 10 The point of the point is to increase the electric field near the point. Small radius curves will have a higher local electric field, eventually creating a localize area where the field is greater than the dielectric strength of the air. This results in what I refer to as "micro-lightning." This microlightning discharges the air (or cloud) before the ... 9 At atmospheric pressure, air and other gases are poor conductors (Insulators) of electricity. Because, they don't have any free electrons to carry current. But, once the free electrons are produced in gas by ionization (they become plasmas), electric discharge occurs. This could be done in many ways such as by applying a large potential difference across a ... 8 AM radio typically transmits at around 1 MHz, FM radio at about 90 MHz. Measurements of the RF spectrum of lightning strikes show a falloff with frequency of about 20 dB per decade in that frequency range, so with FM about 2 decades above AM, you'd expect AM to have about 40dB higher interference from a lightning strike. In addition to that, FM signals ... 8 This video illustrates how a candle flame conducts a high voltage (10,000 volts). Although the ion density is small in a candle flame, they are sufficiently present to conduct electricity. 8 At sufficiently high voltages almost everything conducts due in part to quantum tunneling of electrons. An insulator has a breakdown voltage which is the field strength required before it will start conducting. Related to the breakdown voltage is the dielectric strength which is the minimum voltage over distance ($\mathrm{V}/\mathrm{m}\$) before a material ...

7

In answer to your second question: "Now going with my b) reasoning, wouldn't you be just as safe standing next to a giant conductive pole (i.e. a lightning rod)? Wouldn't the lightning just go through the lightning rod and you'd be 100% safe?" No. A lightning strike can carry a high current, up to 200 kiloamps has been recorded. Not only can the current ...

7

A Lightning rod without earthing is as good as any other conductor laying stray in open. If its not earthed then it wont work at all. There is nothing very fancy about the whole process. You need to connect both ends of a circuit to make current flow. An improper grounding connection can cause disaster sometimes as the lightening may find another route like ...

7

The majority of the energy is dissipated in the travel through the air from the cloud to the ground. The energy goes into heating the air and generating the shockwave that we hear as thunder. I can't give you a single definitive refernce for this, but Googling "energy dissipation lightning" will find lots of relevant articles. You can understand why this is ...

7

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 ...

6

Basically: no cheap, efficient, large-scale battery technology exists. This question gets asked in the world of intermittent renewable energy generation all the time, but it is even harder for lightning because of the extermely high power of the energy burst, so that's an extra problem to solve on top. Also, how do you predict where it will strike? Build a ...

6

Yes it is: lightning in slow-mo In general, both are possible, see: types of lightning

6

It depends on how you define "lightning". When electrons flow from clouds to the earth, ionizing the air and producing light, does your definition include the electrons, the air, the plasma, the light, or a subset? Pedantically speaking, I would say that lightning is the flow of electrons, and to me a flow is an abstract idea (the action of moving in a ...

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 ...

6

A few points: Power lines are the highest objects in the countryside, they are made with giant grounded metal pylons. Lightning wants to go the way of least resistance, so they are nice targets. They ionize the air, this is a strong effect for 220kV+ lines (they even glow purple in a very dark night, the glow comes from something called corona discharges). ...

6

Higher frequencies attenuate faster in air than lower frequencies. The further away a lightning flash the less high frequency components will reach your ear

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