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Fortuna
2009-12-29, 09:08 PM
Yeah. This question arises directly from how scary my group is.

What Ampage and Voltage do you get from a Lightning Bolt spell? How hot is a Fireball?

ZeroNumerous
2009-12-29, 09:10 PM
Q1) Enough.

Q2) Very.

Any further questions can be explained easily: Magic.

Really, D&D does not model physics in the slightest, and attempting to do so just involves headaches for everyone involved and generally the passage of lots of houserules. If you want to start modelling physics in your tabletop games, then I might suggest something with an inherent and consistent physics model already: GURPS.

Yuki Akuma
2009-12-29, 09:13 PM
1) Enough to kill a grown man.

2) Enough to melt gold.

oxybe
2009-12-29, 09:16 PM
fireball is hot enough to burn people, light nearby objects on fire & melt some metals. since gold is mentioned as one of the metals, it reaches at least 1064.18 °C / 1947.52 °F

i don't know the amps/volts lighting bolt produces based on description alone, but it reaches a heat similar to fireball.

Logalmier
2009-12-29, 09:17 PM
What caster level are we assuming the fireball and lightning bolt to be?

Q1) Enough to animate a body stitched from the flesh of the dead. (It's alive! ALIVE!)

Q2) What ZeroNumerous said.

jseah
2009-12-29, 09:56 PM
Here's qn 1)
http://www.giantitp.com/forums/showpost.php?p=7562634&postcount=115
- Natural lightning gives the damage->energy ratio

http://www.giantitp.com/forums/showpost.php?p=7562882&postcount=116
- divided by path length to give energy to damage density

So a lightning bolt, dealing 35 damage over 120ft, has an energy of 4 591 368 J, or around 4.6 MJ

Swordgleam
2009-12-30, 01:39 AM
One of my previous groups had a rule that anyone who discussed physics at the table lost XP for the session. It might be the solution you seek. (The rule was good-natured, but enforced.)

dsmiles
2009-12-30, 09:55 AM
One of my previous groups had a rule that anyone who discussed physics at the table lost XP for the session. It might be the solution you seek. (The rule was good-natured, but enforced.)

Yeah...this.

Ravingdork
2009-12-30, 11:00 AM
RAW, a lightning bolt isn't even dispersed when it hits a body of water (it follows the line like always). That's why it's called magic rather than physics. What makes you think it has ANY kind of ampage?

Longcat
2009-12-30, 11:05 AM
Fireball: Hot enough to burn anyone with less than 10d6 HP to death.

Lightning Bolt: Enough voltage to give anyone with less than 10d6 HP a serious heart condition.

Allanimal
2009-12-30, 11:18 AM
A magical lightning bolt doesn't follow the normal rules of electricity.

That said, if it were like normal electricity/lightning, the voltage between the wizard's finger (or wand or whatever) would be massive (current doesn't need to be super high - 1 Ampere is enough to kill someone) and unless said magic user was floating or had thick rubber soles, the path through its body would most likely have the least resistance and the caster would be the one getting the zap.

A nearby metallic-armored creature could possibly be a path of less resistance, depending on conditions (humidity, for one), but only the first one (no ray extending xx feet no mater how many in between are hit).

I just suspend disbelief even though I'm an electrical engineer (admittedly I deal with low voltage & current so lightning isn't in the realm I normally deal with). It's magic and the game is supposed to be fun.

ericgrau
2009-12-30, 11:24 AM
Yeah. This question arises directly from how scary my group is.

What Ampage and Voltage do you get from a Lightning Bolt spell? How hot is a Fireball?

1. Your PCs don't know enough about electricity to use it, even out of character it seems b/c a lightning bolt isn't very useful. The ampage is high and the voltage is in the millions, but it lasts only for a fraction of the second so the total power is moderate. Hooking that up to anything except a DeLorean is going to be problematic.

2. Enough to melt soft metals like lead, gold, copper, silver, and bronze, but not iron and so on. At least 2000 degrees fahrenheit. It's only for an instant so you still couldn't light most things on fire, except easily flammable things like paper and tinder. This could have reasonable in-game applications without getting crazy.

As for the physics matter, the problem is not that the characters usually don't understand physics. The problem is that the players usually don't understand physics. Any harebrained schemes are usually not feasible. Instead of guessing whenever a player suggests one, make him prove it works before even attempting it in game.

Andras
2009-12-30, 11:23 PM
ampage is high and the voltage is in the millions, but it lasts only for a fraction of the second so the total power is moderate.

The charge is high. If both the current and voltage were high, the power would indeed be high (P = VI). Current (measured in amps) already takes time into account (I = Q/T).

nekomata2
2009-12-30, 11:33 PM
1. Your PCs don't know enough about electricity to use it, even out of character it seems b/c a lightning bolt isn't very useful. The ampage is high and the voltage is in the millions, but it lasts only for a fraction of the second so the total power is moderate. Hooking that up to anything except a DeLorean is going to be problematic.


So what happens if you hook it up to the Apparatus of Kwalish?

Saurus33
2009-12-30, 11:37 PM
Uh, guys? Why are many of you being unhelpful instead of actually trying to answer the question here? They've obviously decided that people know about the physical characteristics of electricity and energy(or at least someone does), and now they are working through and need the information.

What benefit, other than making the unhelpful answerers feel smug, does an answer of "enough to do xd6" have?

Setra
2009-12-30, 11:40 PM
Well according to :roy: a fireball is 1400 Kelvin, if I recall correctly :smalltongue:

Temotei
2009-12-30, 11:42 PM
Uh, guys? Why are many of you being unhelpful instead of actually trying to answer the question here? They've obviously decided that people know about the physical characteristics of electricity and energy(or at least someone does), and now they are working through and need the information.

What benefit, other than making the unhelpful answerers feel smug, does an answer of "enough to do xd6" have?

What benefit does your post have? What benefit does my post have? :smalltongue:

tyckspoon
2009-12-30, 11:51 PM
What benefit, other than making the unhelpful answerers feel smug, does an answer of "enough to do xd6" have?

They're not very helpful, but they are the only answers that can really be determined from the game rules. D&D is not particularly concerned about making its (un)natural phenomena self-consistent. A natural lightning bolt (as described as part of a Thunderstorm in the environmental stuff) randomly deals from 1-80 points of damage (1d10 d8s worth). I'm pretty sure there is no practical way to relate that to the damage dice done by a Lightning Bolt spell or a Shocking Grasp.

Saurus33
2009-12-31, 12:19 AM
Temotei: point being, it isn't particularly respectful of the person asking to ignore the question and instead go off on tangents.

Tyckspoon: good point. It isn't all that consistent, but knowing how much damage a lightning bolt does gives us a basis of comparison from which possible values can be calculated, much like how the energy emitted by a wall of fire was calculated.

Sstoopidtallkid
2009-12-31, 12:59 AM
Tyckspoon: good point. It isn't all that consistent, but knowing how much damage a lightning bolt does gives us a basis of comparison from which possible values can be calculated, much like how the energy emitted by a wall of fire was calculated.Except it really doesn't. By the time you can survive 10d6 damage regularly, you can also jump off of 10 story buildings and walk away afterward. HP is not a number that makes sense in the real world, so using Lightning Bolt's damage to get real-world numbers is doomed to fail.

Saurus33
2009-12-31, 01:08 AM
Wouldn't that actually make it easier?

Edit: an example, post 29.

http://www.giantitp.com/forums/showthread.php?t=134910

The rest of the thread is useful too.

taltamir
2009-12-31, 01:19 AM
2. Enough to melt soft metals like lead, gold, copper, silver, and bronze, but not iron and so on. At least 2000 degrees fahrenheit. It's only for an instant so you still couldn't light most things on fire, except easily flammable things like paper and tinder. This could have reasonable in-game applications without getting crazy.

This puts it above (copper): 1357.77 K, 1084.62 °C, 1984.32 °F
And below (iron): 1811 K, 1538 °C, 2800 °F

the fact that it can deliver enough energy (not temperature, energy) to melt an amount of copper but not enough to set wood on fire; or merely singe a person without killing him, is a physical impossibility.

Also, at the temperatures require to melt copper, it should reduce the tensile strength of iron. probably make it glow red too.

Swordgleam
2009-12-31, 01:27 AM
Uh, guys? Why are many of you being unhelpful instead of actually trying to answer the question here? They've obviously decided that people know about the physical characteristics of electricity and energy(or at least someone does), and now they are working through and need the information.

Sometimes it's more helpful to answer the underlying problem than it is to answer the question as asked. I believe most of us read the opening post as, "My players are / I am a player trying to abuse their spells and citing real-world physics as the justification."

taltamir
2009-12-31, 02:05 AM
Sometimes it's more helpful to answer the underlying problem than it is to answer the question as asked. I believe most of us read the opening post as, "My players are / I am a player trying to abuse their spells and citing real-world physics as the justification."

that...
also, the authors at WOTC fail physics forever. there is simply no way to accurately convey values for such things because of that. I am shocked and awed that the metals they listed it can melt actually have a lower melting point than those they listed it cannot. I am sure it is sheer coincidence.

ericgrau
2009-12-31, 11:10 AM
The charge is high. If both the current and voltage were high, the power would indeed be high (P = VI). Current (measured in amps) already takes time into account (I = Q/T).

You're using terms to cause confusion here. The Power is high but Energy is moderate. Energy is Power x Time. What's the difference between total power and energy in most people's minds? None, outside of doing schoolwork. I challenge you to never again talk about how much "power" you use each month and say "energy" instead. Regardless, the total energy of a lightning bolt is only so-so since it's so brief. This also means the charge is so-so because T is low.



the fact that it can deliver enough energy (not temperature, energy) to melt an amount of copper but not enough to set wood on fire; or merely singe a person without killing him, is a physical impossibility.

Since the energy required to melt copper depends on how much copper you have, there is no conflict whatsoever. The spell can burn paper, which is made of wood, but not wood. Likewise while it's assumed that it melts most copper implements, it probably wouldn't melt a solid bar of copper or a thick solid copper door. Fortunately large objects made of solid copper/gold/bronze/lead almost never exist. Most implements are relatively thin compared to firewood. EDIT: I just checked and the heat of vaporization for the water in the firewood is 10 times higher than the heat of fusion (melting) for copper, meaning the amount of wood that can be burned is much lower than what can be melted.

Pharaoh's Fist
2009-12-31, 11:16 AM
Doesn't Roy cite the approximate temperature range of a Fireball in On the Origin of PCs?

Telonius
2009-12-31, 11:20 AM
Can we assume that all spells of the same level contain the same amount of (magical) energy? Since equal-level wands cost the same amount, it seems reasonable to suspect that they hold the same amount of energy. If that's so, the amount of energy in Fireball is equal to the amount of energy in Lightning Bolt. Since we have a general idea of how hot Fireball can make things, you could probably derive the total amount of energy there; which would be equal to the total amount of energy in Lightning Bolt, since they're the same level. From that, I think you can figure out the voltage and amperage.

Reinboom
2009-12-31, 11:26 AM
Doesn't Roy cite the approximate temperature range of a Fireball in On the Origin of PCs?


Well according to :roy: a fireball is 1400 Kelvin, if I recall correctly :smalltongue:

whitetext :D

valadil
2009-12-31, 11:30 AM
Can we assume that all spells of the same level contain the same amount of (magical) energy?

Are you going by spell level or caster level? If you're basing this on crafting costs, I think spell level * caster level is a closer approximation to the price.

ericgrau
2009-12-31, 11:32 AM
Can we assume that all spells of the same level contain the same amount of (magical) energy? Since equal-level wands cost the same amount, it seems reasonable to suspect that they hold the same amount of energy. If that's so, the amount of energy in Fireball is equal to the amount of energy in Lightning Bolt. Since we have a general idea of how hot Fireball can make things, you could probably derive the total amount of energy there; which would be equal to the total amount of energy in Lightning Bolt, since they're the same level. From that, I think you can figure out the voltage and amperage.

Well, only for lightning. Cold, sonic and acid tend to to less damage.

It takes 0.8 kJ to heat up a cubic meter of air 1 degree celcius. We need about 1100 degrees celcius (1373 kelvin btw) for 880 J per cubic meter. V = 4/3 * pi * r^3 = 950 m^3. E = 880 J * 950 m^3 = 836,000 kJ = 836 MJ.

The breakdown voltage of air is 3 million volts per meter. Lightning bolt has a range of 120 feet or 36.6 meters. So the voltage is 110 million volts. The charge is 836 MJ / 110 million volts = 7.6 C. The current I = Q / t. t = 30 microseconds (millionths of a second) for an average lightning bolt, making I = 7.6 / (30 * 10^-6) ~= 250,000 amps. P = VI = 27,500 gigawatts. Doc Brown would be satisfied. Go get me a DeLorean.

EDIT: After a look at real lightning bolts on wikipedia, if the air has a chance to ionize beforehand the voltage can be up to 30,000 times lower and thus current up to 30,000 times higher. Power and energy remain unchanged. Given that a D&D lightning bolt doesn't immediately take the easier path straight to the ground, having the spell ionize an easy pathway to guide the bolt to a better target would make a whole lot of sense both for practical use and for imitating nature.

It'd also make for great flavor text: "You suddenly smell something like the fresh air when it rains, but stronger, the moment before you are struck with a lightning bolt."

Talya
2009-12-31, 11:33 AM
Will somebody please think of the catgirls?

ericgrau
2009-12-31, 11:44 AM
Sorry, struck by lightning.

Fenix_of_Doom
2009-12-31, 12:27 PM
RAW, a lightning bolt isn't even dispersed when it hits a body of water (it follows the line like always). That's why it's called magic rather than physics. What makes you think it has ANY kind of ampage?

Why would lightning disperse if it hits water? water conducts better than air right, so if anything you should be able to push more charge per cm2 and thus narrow the bolt.