J
John S
Guest
On 7/28/2020 12:11 PM, bitrex wrote:
My Units application says:
You have: ohms
You want:
Definition: ohm = V/A = 1 kg m^2 / A^2 s^3
On 7/28/2020 12:28 AM, Phil Allison wrote:
Ricketty C wrote:
=================
Where did you come up with this?
R = (kg/Coulomb^2) * meter^2 / second
** Physical quantities have \"dimensions\" - so suspect that is what it
hints at. But I believe R is a dimensionless quantity.
That may be the slight of hand you are meant to see.
....   Phil
What dimensions resistance has depends on how you pick your fundamental
units. in CGS everything is unambiguously derived from the centimeter,
gram, and second and volts/amp oddly ends up having dimensions of
centimeters/second.
In SI volts/amp has dimensions of (kg/Coulomb^2) * meter^2 / second.
My Units application says:
You have: ohms
You want:
Definition: ohm = V/A = 1 kg m^2 / A^2 s^3
The \"sleight of hand\" such as it is is that Power = V*I = I^2*R = V^2/R
are all equivalent ways of saying the same thing, if you start with the
physics fact that V*I has units of power, and the (assumption,
empirically-invented idea that sometimes holds) relation that V = IR.
Substituting the different ways of expressing the power relation into
each other, or any way of expressing V = IR for anything there, results
in no novel information, even if you use the dimensions rather than the
symbols.
So it\'s 9 lines of saying the same thing in different ways and then he
ends up with an equation for power same as he started with. And then on
the last line drops the R and a factor of 1/second and ends up with
dimensions of energy, but with no justification at all to do that.