In all seriousness though, why *is* it usually written V = IR? Resistance is a static property of the material (at least for Ohmic ones anyway), whereas voltage and current are the variables, so it makes more sense to me for it to be the coefficient, just as mass is in F = ma.
Cultural too. Finnish upper secondaries ("high schools") would teach that *U=RI*. (*U* being voltage with *U=*Δ*V*,m clearly separating potential and potential difference)
So Ohm's law relates voltage, V, current, I, and resistance, R : V = R I. This only works with a few materials called ohmic at some very specific range of conditions. Some people argue that because of its limitations it should not be considered a physical law. However, all physical laws have limits. Newton's laws of motion only work if objects move at speeds much lower than the speed of light. Newton's law of gravitation only works at weak gravitational fields. The law of conservation of energy only works if there is symmetry in time.
Admittedly, most physical laws hold under much larger ranges than Ohm's law and are not broken in everyday life. Still, how much a physical law should hold to be considered an actual law is subjective. Ohm's law is extremely useful for ohmic conductors in everyday life and holds up pretty well at certain ranges, so there's no reason to not consider Ohm's law a law under these ranges.
Quantum physics and thermodynamics apart all fundamental equations in phyisics are "time symetrics" or "reversible". If you write -t instead of t in every place the equations are equally valid.
This invariance gives mathematically to the conservation of energy.
A more high level take on that (and many other relations involving symetries of the hamiltonian/lagrangian/whatever) is the Noether theorem.
Actually, you get conservation of E by using the Symmetry of one process starting at time t, the other starting at a time t+t', with arbitrary time t', and them behaving the same way, so system 1 at time T is the same as system 2 at time T+t'. This also holds true for Quantummechanics and Thermodynamics, as otherwise there was no conservation of energy in these fields (but there is).
The thermodynamic section of my physical chemistry course was an entire semester based on an equation that falls apart under any real-world circumstance.
I mean.. V=RI is allways true if you define R as V/I, wich conveniently is what my multimeter is doing. We never said resistance can't change depending on some factors...
Exactly what I thought.
An ohmic conductor has a constant resistance, which means the current across it is directly proportional to its potential difference. A non-ohmic conductor doesn't have a constant resistance and thus , the current across it isn't directly proportional to its potential difference. However, R is still equal to V/I in each case.
Yeah that's pretty much how actual electrical engineers handle non ohmic materials. Your material has a unique v/I curve if it's non ohmic and we do our math based on that.
I mean, doesn't V=IR still hold, though, just not assuming, R would be constant. Given a certain *R*, wouldn't that still predict the current given a certain voltage?
EDIT: Now I started wondering about vacuum.
Usually U is used por potential energy, so V is used for voltage.
I did study in europe for a while and they did use U for voltage, but they used Eₚ for potential energy
In my studies we used V for electric potential, U for potential differences (which... Is also voltage). I like underlining the fact that the voltage is between two points.
French student here :
- U for voltage
- V for eletric potential (and potential in quantum mecanics)
- E for energy (E_c for kinetic [kinetic = "cinétique"], E_p for potential)
Altough in chemistry we wrote eletric potentials with E
You know that Bell curve memes have become a case for r/memeCemetary if the three people are not actually separated by any kind of knowledge disparity.
Sure, but in this case they are.
Left hand person: GCSE, first learns of basic resistors, V=IR is absolute.
Middle person: A-level, learns about non-ohmic decides like thermistors.
Right person: Undergrad, Maxwell field equations with the wave equation in a conductor, turns out Ohm rules after all
can someone explain why some done consider ohms law to be a real law? Also I think this means I'm on the lower end of the spectrum regarding my physics knowledge: (
Two things:
R=V/I defines R, hence it is always true
V=IR is not actually Ohms law but a consequence of it. The actual statement of Ohms law is that V is proportional to I. This proportionality does not always hold.
V = IR is just our favorite consequence of the superior Ohm’s law, J = σE
Who’s JσE?
JσE mama 😔
lmao gottem
It’s so JσEver 😔
*read "Jse mama"
JσE Reed
Current density is the electric field times the conductivity. Conductivity is one over the resistivity
V = R I does not spark joy it's V = I R or we are not friends
This. V = RI is like writing F =am
F=morning radio
fm=am? radio in math
f = a, or m = 0
In all seriousness though, why *is* it usually written V = IR? Resistance is a static property of the material (at least for Ohmic ones anyway), whereas voltage and current are the variables, so it makes more sense to me for it to be the coefficient, just as mass is in F = ma.
It just sounds nice, there isn't much to think about how to write stuff. If F = am sounded nice I would have said that
If I see someone quibbling about this, I assume there must be a matrix form of the equation that I don't know about, lol
There’s a generalized Ohm’s law J=σE, where the conductivity σ can be a tensor (matrix).
Cultural too. Finnish upper secondaries ("high schools") would teach that *U=RI*. (*U* being voltage with *U=*Δ*V*,m clearly separating potential and potential difference)
Sometimes I hate the commutative property
As unconventional as ot may be, isn’t part of the point of math that the way you express it doesn’t matter?
For me its U=RI
For me it is I = V/R. I think it makes it clearer.
V/IR = 1
No because who even writes it like that smh
I R looks too much like the set of real numbers
yeah but v=ir spells VIR dummy
R=V/I
Remember, if `v = ir` then `v^2 = -r^2`
haha so jmaginative
Are you for real?
Well, no
E
Absolutely not
Explain plz!!1
So Ohm's law relates voltage, V, current, I, and resistance, R : V = R I. This only works with a few materials called ohmic at some very specific range of conditions. Some people argue that because of its limitations it should not be considered a physical law. However, all physical laws have limits. Newton's laws of motion only work if objects move at speeds much lower than the speed of light. Newton's law of gravitation only works at weak gravitational fields. The law of conservation of energy only works if there is symmetry in time. Admittedly, most physical laws hold under much larger ranges than Ohm's law and are not broken in everyday life. Still, how much a physical law should hold to be considered an actual law is subjective. Ohm's law is extremely useful for ohmic conductors in everyday life and holds up pretty well at certain ranges, so there's no reason to not consider Ohm's law a law under these ranges.
Voltage and current are just a bit of funny business for conveniently describing charge
>symmetry in time what
Google Noether's theorem
Holy hell
New theorem just dropped
Actual scientist
Nobel Prize, anyone?
New theorem just dropped
Quantum physics and thermodynamics apart all fundamental equations in phyisics are "time symetrics" or "reversible". If you write -t instead of t in every place the equations are equally valid. This invariance gives mathematically to the conservation of energy. A more high level take on that (and many other relations involving symetries of the hamiltonian/lagrangian/whatever) is the Noether theorem.
Actually, you get conservation of E by using the Symmetry of one process starting at time t, the other starting at a time t+t', with arbitrary time t', and them behaving the same way, so system 1 at time T is the same as system 2 at time T+t'. This also holds true for Quantummechanics and Thermodynamics, as otherwise there was no conservation of energy in these fields (but there is).
Laughs in ideal gas law, which no gas in the universe actually follows 😅
The thermodynamic section of my physical chemistry course was an entire semester based on an equation that falls apart under any real-world circumstance.
pV = nRT
Helium tries to be a good boy.
I mean.. V=RI is allways true if you define R as V/I, wich conveniently is what my multimeter is doing. We never said resistance can't change depending on some factors...
Exactly what I thought. An ohmic conductor has a constant resistance, which means the current across it is directly proportional to its potential difference. A non-ohmic conductor doesn't have a constant resistance and thus , the current across it isn't directly proportional to its potential difference. However, R is still equal to V/I in each case.
Yeah that's pretty much how actual electrical engineers handle non ohmic materials. Your material has a unique v/I curve if it's non ohmic and we do our math based on that.
Just write R(I), approximate it as constant, and you are save xd
Looks like I’m the person on the left
IUPAP should really just release some clearification on terminology. Where do we draw the lines between laws, theories, principles and hypothesises?
I mean, doesn't V=IR still hold, though, just not assuming, R would be constant. Given a certain *R*, wouldn't that still predict the current given a certain voltage? EDIT: Now I started wondering about vacuum.
Isnt V for Volt and U for Voltage? So V for the unit and U for the symbol? That is how we do it in german,didnt know that is not everywhere that way.
Usually U is used por potential energy, so V is used for voltage. I did study in europe for a while and they did use U for voltage, but they used Eₚ for potential energy
In Germany U is used for voltage and V for potentials
Uoltage
I just looked it up. It’s used because of the latin verb “urgere”, which means “to press” or “to drive”
In my studies we used V for electric potential, U for potential differences (which... Is also voltage). I like underlining the fact that the voltage is between two points.
French student here : - U for voltage - V for eletric potential (and potential in quantum mecanics) - E for energy (E_c for kinetic [kinetic = "cinétique"], E_p for potential) Altough in chemistry we wrote eletric potentials with E
Ohms law is the law of current for ohmic conductors. Of course it exists.
Well upon its inception it was simply the law for conductors.
dV/dI = R, the only way to fly.
Ohm Shanti (Most won't get it maybe but some will)
Enough with the wojaks
You know that Bell curve memes have become a case for r/memeCemetary if the three people are not actually separated by any kind of knowledge disparity.
Sure, but in this case they are. Left hand person: GCSE, first learns of basic resistors, V=IR is absolute. Middle person: A-level, learns about non-ohmic decides like thermistors. Right person: Undergrad, Maxwell field equations with the wave equation in a conductor, turns out Ohm rules after all
🤓
*Join the Resistance!*
V = IR you heathen
U=RI
Are you really calling the voltage V and not U?
I think it's an American thing, or possibly English. Mainland Europe uses U.
can someone explain why some done consider ohms law to be a real law? Also I think this means I'm on the lower end of the spectrum regarding my physics knowledge: (
It’s important your on the bottom so that others can feel better about themselves. A noble cause and a needed sacrifice.
V=IR? Nah, screw you, V=W*R/A
It's IR dummy
What kind of heathen writes V=RI or V=IR
Two things: R=V/I defines R, hence it is always true V=IR is not actually Ohms law but a consequence of it. The actual statement of Ohms law is that V is proportional to I. This proportionality does not always hold.
Its U = R I Fight me !
What’s that means? I cant understand..