I'm a fan of the movie Back to the Future, and in the movie it is stated that a bolt of lightning contains 1.21 gigawatts. Is it true? I always wanted to ask that to specalists but kept forgetting!!!

I thought it was 1.21 Jigawatts, not something real, just designed to sound really, really big!!

Some people pronounce giga- like "jiga".

Actually the official script of the movie spells it "jigowatts", so the intention was to create a crazy unit of measurement. But I just wanna know how mant watts are in a bolt of lightning.

well...a gigawatt is equivalant to one billion watts. a watt is one joule per second....


so i guess 1.21 Gigawatts may be a lot...

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In fact a typical bolt of lightning is somewhere around a gigawatt, though occasionally you can get much larger than that (a hundred to a thousand times more powerful!) Of course, it's very short-lived, so the amount of energy isn't as large as it might seem from the power, though still pretty impressive.

One of my professors pronounces giga with a soft g. I have a really, really difficult time not laughing at her...

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I took a week of Ancient Greek before I quit; In that class, 'giga' is said 'Jiga'. So.. maybe its only half wrong.

Found this in IMDB tivia section - which probably means someone got it from the Back to the Future DVD special features.......or just made it up:

In the film's script the word "gigawatt" is spelt "jigowatt". Bob Gale and Robert Zemeckis had been to a science seminar and the speaker had pronounced it "jigowatt".

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For another fun number in the Giga range, the heat generating elements of current microprocessors dissipate heat on the order of several gigawatts/m^3. Thank God they're tiny

Also, check out the
Wikipedia energy scale. You'll find out that a bolt of lightning releases about the same energy as a tankful of gasoline.

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I just checked my Ame.Her.Dic., and the soft g is the first pronunciation every time (jigabit, jigabyte, jigacycle, jigahertz). That's probably the way it is on dictionary.com too then.

What does it mean that it's first? Does the American Heritage Dictionary order the pronunciations according to how prevalent they are?

Soft G has always been the correct pronunciation.

But the American tech industry got to it first, and will be abused for the rest of time. Might as well rewrite the rule.

The first time I saw it, I thought he said 12.21, not 1.21. I'm still not 100% certain he didn't say 12.21 gigawatts. Not really adding anything material to the debate I guess, just my own musings on it.

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As a youngster one of my favorite exhibits at the Museum of Science & Industry in Chicago was the lightning bolt generator. Can't remember the proper terminology, but they had a stack of monstrous capacitors in the middle of the room that were charged up, I believe it was 10 units of 100,000 volts or watts each. They sounded a bell, at which time everyone was warned to hold this rail that went around the display. The stack was then discharged via a rod sticking out the top of the stack (which I'm guessing was 12 to 15' tall). A bolt of lightning then went from the top of the stack to a copper pipe that circled the ceiling at the perimeter of the room. The noise and flash were fantastic.

I could have some details wrong as it has been a long time; but I thought it was 1 million volts.

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Ame.Her.Dic. (1970, p.XLII) says "All pronunciations given are acceptable in all circumstances. When more than one is given, the first is assumed to be the more common, but the difference in frequency may be insignificant."

IIRC, the Oxford Dictionary lists definitions in the order that they entered the language. I'm not sure about the pronunciations.

No, it's 1.21 gigawatts.

Well, the pronunciation issue is quite interesting, but how many watts are there in a bolt of lightning after all? Is Grey above correct, the typical lighnting has about 1 gigawatt???

If you have a machine that needs 1.21 gigawatts to work, would a bolt of lightning suffice???


What is a watt, afterall? And a volt? I never understood exactly what it means.

The basic formula is: Watts = Volts x Amperes
IIRC, a "typical" lightning bolt is estimated to have about 30 million volts and about 100K Amps. This gives W= 300 billion (or 300 giga) watts! However, some of that energy is lost through radiative heat (which results in thunder), thus the amount that could be potentially harnessed at the point of strike would be considerably less. And of course, it's only for an instant.

edited to correct figures

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Watts is not enery, watts is power! Energy is power times time. So, if you've 300GW for a millionth of a second, the energy in this would be 300000Ws=Nm=J, which would be 83kWh, which is not so impressive in terms of energy.

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It is not really meaningful to ask how many watts a bolt of lightning contains, the number just tells you how quickly it disipates energy.

It's a figure I recalled, and doing a quick Google search, I see similar numbers. This introductory textbook, for example, agrees, since it gives the rough voltage as 100,000 V, the current as approximately 100 A, and power is voltage times current squared. Of course, this is certainly an estimate, and I do know that the high end can be significantly higher, as I mentioned.

If it only needs to be powered for the fraction of a second that is the typical duration of a lightning bolt, and wasn't too picky about the power level being very precise or very constant, I suppose it might.

A watt is unit of power, and power is energy over time. That is, a 100 watt light bulb uses 100 joules of energy every second, changing that energy from electrical energy to light and heat. If you have a 100 watt light bulb on for 2 seconds, and a 200 watt light bulb on for 1 second, they will both have used the same amount of energy.

A volt is the unit of electric potential difference (what we normally call a "voltage" - that's like calling length "yardage", though interestingly nobody ever says "meterage"), a way of measuring how the electric fields present are trying to push charges around. Perhaps the best way to think of it is by analogy to gravitational potential, so you can think of a larger voltage as being "higher". If given a path to do so, electric charge will flow from a higher potential to a lower one, just like water would would flow to a lower level.

And as with differences in height, it only really makes sense to talk about differences in height (how high is something that's at 1000 m, if I don't specify that I mean 1000 m above sea level, or 1000 m above the ground, or use some other reference?). Generally when working with electrical circuits, our standard of reference is the ground, literally a wire connected by some easily conducting path to the Earth. Since the Earth is really big, any charge that might accumulate will be negligible, and the Earth as a whole can be considered uncharged.

Does that help?

So there is no machine that needs an X-number of Watts, for it all depends on for how long those watts stream in.

So the DeLorean of Back to the Future woudn't actually need 1.21 gigawatts, rather a certain number of volts???

Funny thing, but in Portuguese we do: metro > metragem, quilómetro > quilometragem. Our word for "yard" is "jarda" but it's only used in medieval texts or translating American stuff, so we don't have "jardagem".


Helps a lot!!! Thanks!!!

Another question: what is electricity? What happens when a wire conducts electricity? Do electrons jump from atom to atom in the copper? What exactly is being conducted?

As Wikipedia points out, it is less energy than a modest tankful (12gallons~45liters) of gasoline. As kucharek points out, its just that amount of energy is released over a shorter time, and not during a 4 or 5hour drive. BABBlers, think about that next time you pop into one of those monstrosities called an SUV or a pick-up truck.

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Most machines are designed for a certain voltage as well as wattage. For example, that lightbulb expects 100 watts of power, delivered at about 120 volts, which means that it's drawing a current of about 1.1 amps. You could theoretically have a current-limited voltage source that could provide the full voltage, but not that much power, and the light would be dimmer. How sensitive a given machine is to having exactly the right voltage and power depends on the characteristics of the machine (typically, the more complex it is, the more important it is to provide exactly what it expects).

So remember that the voltage difference corresponds to an electric field that exerts on force on charged objects. The atoms are pretty hard to move, since they're held in place by the other atoms, but if the force is large enough, it will push the electrons along. How much force is required to do that depends on the material. For an insulator, the force needed is very large, so relatively little current flows for a given voltage. For good conductors like metals, it turns out that because of the details of the electron configuration in each atom, there are some electrons that remain trapped in the material as a whole, but aren't particularly strongly bound to any particular atom.* There ends up being roughly one such electron per atom for the good conductors. So if you apply any field at all, these electrons will flow very easily and you see a current flowing.

As an aside, the net flow of charge is very quick. So if you push a few electrons in one end of a copper wire, the time it takes for electrons to come out the other side is very short. But the speed of the electrons themselves isn't all that fast, comparable to a walking pace. The electrons you push in at this end repel the electrons nearest them, which move a little way down the wire, increasing the number of electrons in that part of the wire, so the electrons there are repelled, and move a little, and so forth.

* I won't go into the details here, but one of the impressive feats of quantum theory is being able to show just how this macroscopic property of a material (how well it conducts electricity) arises from the arrangement of electrons in each atom, and how the energy levels of those electrons change when the atoms are close together in a solid.

Once we've sold this question, we can move on to how the time train in part 3 could operate just on steam!

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Yeah, lets turn this into a Back to the Future science thread.

Other questions would be Mr. Fusion - the gadget Doc adapted to the DeLorean in 2015 to replace the plutonium fission device that powered the Flux Capacitor. Could fusion ever work with everything? I mean, Mr. Fusion turns even garbage into energy!

What about the hover technology - in 2015 (unfortunately we're not even close yet) things can float in the air - the hoverboard, for instance.

What about time travel itself - if possible, what sorts of paradoxes would time travel into the past cause? Would it destroy the "fabric of space-time continuum"? The universe?

The time train is really tough to explain - how could steam generate 1.21 gigawatts?

And dont' get me started on gigabytes and gibibytes...