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- Thread starter T0mr
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- #2

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Put amps in terms of coulomb. One amp is a coulomb per second isnt it? Look that up to make sure.

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- #6

davenn

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they are not related ... what are you trying to do ?

Dave

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In SI there is no way to write a dimensionally consistent equation with only C on one side and only powers of m, kg, and s on the other side. This is what it means for a unit to be a base unit, as Jimmy said.

In the cgs system the Statcoulomb is a derived unit, but Maxwells equations are different in cgs units than in SI.

- #8

Borek

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formula for the Coulomb in terms of m, kg, s

It is like asking for a formula for m in terms of kg.

- #9

DrClaude

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I always express mass in kgIt is like asking for a formula for m in terms of kg.

- #10

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m = (kg^5*s^3)/(C^4*m^4)

That means C would have to have units ((kg^5*s^3)/m^5)^(1/4) for the equation to be dimensionally correct in this case. It seems to be the consensus that it is not posssible to write the coulomb in any other way than A*s. I completely get that writting kg in terms of m and s seems impossible. But is there a formal proof that what we call a kilogram cannot be expressed in terms of other base units somehow. I am more inclined to accept that kg cannot be written in terms of m and s without some kind of proof. But something about the Ampere makes me question it.

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Consider two infinitely long parallel wires 1 meter apart. If each wire carries 1 A then the force between wires per meter of wire is 2 10

- #12

f95toli

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But is there a formal proof that what we call a kilogram cannot be expressed in terms of other base units somehow. I am more inclined to accept that kg cannot be written in terms of m and s without some kind of proof. But something about the Ampere makes me question it.

You can't "prove" anything about the SI; the SI is an

The whole point of the SI is that it is a practical and -reasonably- self consistent system of units that is used internationally.

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- #14

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Then that equation is wrong.I am getting equations like this:

m = (kg^5*s^3)/(C^4*m^4)

- #15

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There is a proof, it is very simple:

The Ampere is a base unit by definition of Ampere. (as agreed by vote)

Base units cannot be written in terms of other base units by definition of base unit.

Therefore, the Ampere cannot be written in terms of other base units.

QED.

Again, you can do this in cgs units, not SI units. But that changes the physics equations.

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Coulomb is also a fundamental unit, like those for length, mass and time.

- #17

Borek

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Coulomb is also a fundamental unit

No, it is derived - 1C=1A×1s.

Unless we are thinking about something else when we say "fundamental".

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- #19

Borek

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I am not sure how it was historically, but as of today, Ampere is a basic unit - by definition.

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It is like asking for a formula for m in terms of kg.

?????how so ???????

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DaleSpam said:There is a proof, it is very simple:

The Ampere is a base unit by definition of Ampere. (as agreed by vote)

Base units cannot be written in terms of other base units by definition of base unit.

Therefore, the Ampere cannot be written in terms of other base units.

QED.

Just because the Ampere was defined to be a base unit does not mean that it cannot be defined in terms of other base units. Even if everyone in the world agrees that the Ampere is a base unit, and that by the definition of the base unit the base unit cannot be written in terms of other base units, without a rigorous proof there is no way to know with certainty that the set of definitions is logically consistent (meaning that the definitions do not contradict each other.)

For example imagine there are only two units: the star unit and the atom unit. We define these two units to be base units because we do not notice for some reason that stars are made of atoms. We define the base unit to mean a unit that cannot be defined in terms of other base units, and so we have created a logically inconsistent set of definitions.

- #22

Borek

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?????how so ???????

You can't express charge using m/kg/s just like you can't express meters using kilograms.

- #23

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How is this helpful???You can't express charge using m/kg/s just like you can't express meters using kilograms.

You cant express s as kg....is that any better....random examples of what cannot be done ??

- #24

Borek

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How is this helpful???

You cant express s as kg....is that any better....random examples of what cannot be done ??

It was an analogy. From what OP stated he was aware of the fact kg/m/s are independent units, and I was showing him how he wants to do something impossible, using example that he should understand.

s as kg would work exactly the same, but we are derailing the thread.

- #25

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It was an analogy. From what OP stated he was aware of the fact kg/m/s are independent units, and I was showing him how he wants to do something impossible, using example that he should understand.

s as kg would work exactly the same, but we are derailing the thread.

Mine was also an analogy....you are correct...the thread is being derailed by an analogy that is no use/help

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