Vacuum permittivty with alternative Standard-Unit for meters

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Discussion Overview

The discussion revolves around the implications of redefining the meter as 1.1 times its current value on the vacuum permittivity (ε₀). Participants explore how this change affects the calculations of ε₀ and related physical constants, considering both historical and modern definitions of units.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant calculates the new value of vacuum permittivity (ε₀") as ε₀ multiplied by 1.1, suggesting that this is straightforward but complicated by the need to convert Farads and other units.
  • Another participant references the modern definition of the ampere and the meter, proposing that if the meter is redefined, the speed of light (c) would also need to be adjusted accordingly, leading to an increase in ε₀ by a factor of 1.1.
  • One participant questions whether the reduced value of the meter would also necessitate a change in the reduced Planck constant (ħ), suggesting that ε₀" could become ε₀ multiplied by 1.1 cubed if kg and seconds remain unchanged.
  • A later reply indicates that while it is not necessary to change ħ, it is an option that could be considered.

Areas of Agreement / Disagreement

Participants express differing views on whether the redefinition of the meter should also affect other constants like ħ, indicating that there is no consensus on the implications of the proposed change.

Contextual Notes

Participants note that the calculations depend on the assumptions made about the constancy of other physical constants and the definitions of units, which remain unresolved.

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TL;DR
Value of Permettivity when 1m would be 1,10m
I was wondering: what would be the value of Vacuum Permettivity in the case 1 meter (say 1m") would be defined as the distance we nowadays see as 1,10 meters.

At first this looks easy: ##\varepsilon0 = 8.8541878128 \cdot 10{^{12}}## F / m with normal meters
so ##\varepsilon0" = \varepsilon0 \cdot 1.1##
##\varepsilon0" = 9.739660659408 \cdot 10{^{12}}## F / m" with converted meters.

However, when I look at Farads, this is defined as $$\frac{s^4 \cdot A^2}{m^2 \cdot kg}$$ so Farads should be converted too.

And Amperes are defined as:
"The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed one metre apart in vacuum, would produce between these conductors a force equal to ##2 \cdot 10^{−7}## Newtons per metre of length."

which also involves meters, and Newtons, which are defined as $$\frac{kg \cdot m}{s^2}$$

this all makes it too tough for me.

So, in short, my question is: is the calculated version of E0" correct?
 
Last edited:
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GoodQuestion said:
And Amperes are defined as:
"The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed one metre apart in vacuum, would produce between these conductors a force equal to 2⋅10−7 Newtons per metre of length."
That is the old definition. The modern definition is: "The ampere, symbol A, is the SI unit of electric current. It is defined by taking the fixed numerical value of the elementary charge e to be ##1.602176634×10^{−19}## when expressed in the unit C, which is equal to A s, where the second is defined in terms of ##∆ν_{Cs}##."

see: https://www.bipm.org/utils/common/pdf/si-brochure/SI-Brochure-9-EN.pdf

GoodQuestion said:
I was wondering: what would be the value of Vacuum Permettivity in the case 1 meter (say 1m") would be defined as the distance we nowadays see as 1,10 meters.
Under the current definitions of the SI the meter is defined as: "The metre, symbol m, is the SI unit of length. It is defined by taking the fixed numerical value of the speed of light in vacuum c to be 299792458 when expressed in the unit m/s, where the second is defined in terms of ##∆ν_{Cs}##."

So, if 1 METRE = 1.1 metre then c = 299792458 metre/second = 272538598 METRE/second

Then, since in the current SI we have $$\epsilon_0=\frac{e^2}{4 \pi \alpha \hbar c}$$ Thus, keeping all other SI defining constants the same and keeping physics the same, we simply have a reduction in the numerical value of c by a factor of 1.1 and thus an increase in the numerical value of ##\epsilon_0## by a factor of 1.1

GoodQuestion said:
So, in short, my question is: is the calculated version of E0" correct?
Yes, but you shouldn't write it in units of F/m since you have changed the units.
 
Last edited:
Shouldn't ##\hbar## change also, because there's a meter in there as well?

Assuming the value of KG en second stays the same, shouldn't this lead to ##\varepsilon0##" becomes ##\varepsilon0 \cdot 1,1{^3}## ?
 
GoodQuestion said:
Shouldn't ##\hbar## change also, because there's a meter in there as well?
It is not necessary, but you certainly could do that if you wish.
 

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