A question for all you scientists out there:

In the Wikipedia table of unit conversions, some factors have some numbers in brackets on the end, for instance:

= Bohr radius of hydrogen ≈ 5.2917721092(17)×10−11 m

Does the (17) represent an additional two significant figures that they are not really sure about, or what?

The Rev Dodgson said:

A question for all you scientists out there:

In the Wikipedia table of unit conversions, some factors have some numbers in brackets on the end, for instance:

= Bohr radius of hydrogen ≈ 5.2917721092(17)×10−11 m

Does the (17) represent an additional two significant figures that they are not really sure about, or what?

Note the words most probable
The Bohr radius (a₀) is a physical constant, equal to the most probable distance between the nucleus and the electron in a hydrogen atom in its ground state (non-relativistic and with an infinitely heavy proton). It is named after Niels Bohr, due to its role in the Bohr model of an atom. Its value is 5.29177210903(80)×10⁻¹¹ m.

Tamb said:

The Rev Dodgson said:

A question for all you scientists out there:

In the Wikipedia table of unit conversions, some factors have some numbers in brackets on the end, for instance:

= Bohr radius of hydrogen ≈ 5.2917721092(17)×10−11 m

Does the (17) represent an additional two significant figures that they are not really sure about, or what?

Note the words most probable
The Bohr radius (a₀) is a physical constant, equal to the most probable distance between the nucleus and the electron in a hydrogen atom in its ground state (non-relativistic and with an infinitely heavy proton). It is named after Niels Bohr, due to its role in the Bohr model of an atom. Its value is 5.29177210903(80)×10⁻¹¹ m.

Thanks Tamb.

Where was that from?

I note the numbers on the end, and number of SF, are different.

Also is there a source better than Wikipedia for getting a comprehensive list of conversion values?

Preferably in plain csv format or similar.

The Rev Dodgson said:

Tamb said:

The Rev Dodgson said:

A question for all you scientists out there:

In the Wikipedia table of unit conversions, some factors have some numbers in brackets on the end, for instance:

= Bohr radius of hydrogen ≈ 5.2917721092(17)×10−11 m

Does the (17) represent an additional two significant figures that they are not really sure about, or what?

I just searched for your Bohr radius of hydrogen ≈ 5.2917721092(17)×10−11 m and there are a heap of sites.

Note the words most probable
The Bohr radius (a₀) is a physical constant, equal to the most probable distance between the nucleus and the electron in a hydrogen atom in its ground state (non-relativistic and with an infinitely heavy proton). It is named after Niels Bohr, due to its role in the Bohr model of an atom. Its value is 5.29177210903(80)×10⁻¹¹ m.

Thanks Tamb.

Where was that from?

I note the numbers on the end, and number of SF, are different.

The Rev Dodgson said:

A question for all you scientists out there:

In the Wikipedia table of unit conversions, some factors have some numbers in brackets on the end, for instance:

= Bohr radius of hydrogen ≈ 5.2917721092(17)×10⁻¹¹ m

Does the (17) represent an additional two significant figures that they are not really sure about, or what?

The (17) represents the uncertainty in the last two digits of the value, not additional figures.

btm said:

The Rev Dodgson said:

A question for all you scientists out there:

In the Wikipedia table of unit conversions, some factors have some numbers in brackets on the end, for instance:

= Bohr radius of hydrogen ≈ 5.2917721092(17)×10⁻¹¹ m

Does the (17) represent an additional two significant figures that they are not really sure about, or what?

The (17) represents the uncertainty in the last two digits of the value, not additional figures.

So +-17?

The Rev Dodgson said:

A question for all you scientists out there:

In the Wikipedia table of unit conversions, some factors have some numbers in brackets on the end, for instance:

= Bohr radius of hydrogen ≈ 5.2917721092(17)×10−11 m

Does the (17) represent an additional two significant figures that they are not really sure about, or what?

How many decimal points does one need to include?

The Rev Dodgson said:

btm said:

The Rev Dodgson said:

A question for all you scientists out there:

In the Wikipedia table of unit conversions, some factors have some numbers in brackets on the end, for instance:

= Bohr radius of hydrogen ≈ 5.2917721092(17)×10⁻¹¹ m

Does the (17) represent an additional two significant figures that they are not really sure about, or what?

The (17) represents the uncertainty in the last two digits of the value, not additional figures.

So +-17?

No, ±17×10^-21; the last two digits of the value. That means the value is between 5.2917721075×10^-11 and 5.2917721109×10^-11

roughbarked said:

The Rev Dodgson said:

A question for all you scientists out there:

In the Wikipedia table of unit conversions, some factors have some numbers in brackets on the end, for instance:

= Bohr radius of hydrogen ≈ 5.2917721092(17)×10−11 m

Does the (17) represent an additional two significant figures that they are not really sure about, or what?

How many decimal points does one need to include?

For most practical purposes 3 or 4 significant figures is fine, but I want to get the actual agreed number to however many numbers they have.

btm said:

The Rev Dodgson said:

btm said:

The (17) represents the uncertainty in the last two digits of the value, not additional figures.

So +-17?

No, ±17×10^-21; the last two digits of the value. That means the value is between 5.2917721075×10^-11 and 5.2917721109×10^-11

Ah, yes. 2 × 17 =34

btm said:

The Rev Dodgson said:

btm said:

The (17) represents the uncertainty in the last two digits of the value, not additional figures.

So +-17?

No, ±17×10^-21; the last two digits of the value. That means the value is between 5.2917721075×10^-11 and 5.2917721109×10^-11

OK, that’s what I meant :)

Seems Tamb found a more precise figure then.

Tamb said:

The Rev Dodgson said:

A question for all you scientists out there:

In the Wikipedia table of unit conversions, some factors have some numbers in brackets on the end, for instance:

= Bohr radius of hydrogen ≈ 5.2917721092(17)×10−11 m

Does the (17) represent an additional two significant figures that they are not really sure about, or what?

Note the words most probable
The Bohr radius (a₀) is a physical constant, equal to the most probable distance between the nucleus and the electron in a hydrogen atom in its ground state (non-relativistic and with an infinitely heavy proton). It is named after Niels Bohr, due to its role in the Bohr model of an atom. Its value is 5.29177210903(80)×10⁻¹¹ m.

Looks like it came from:
https://en.wikipedia.org/wiki/Bohr_radius

So the Wikipedia values are inconsistent by 8×10⁻22 m.

The Rev Dodgson said:

Tamb said:

The Rev Dodgson said:

A question for all you scientists out there:

In the Wikipedia table of unit conversions, some factors have some numbers in brackets on the end, for instance:

= Bohr radius of hydrogen ≈ 5.2917721092(17)×10−11 m

Does the (17) represent an additional two significant figures that they are not really sure about, or what?

Note the words most probable
The Bohr radius (a₀) is a physical constant, equal to the most probable distance between the nucleus and the electron in a hydrogen atom in its ground state (non-relativistic and with an infinitely heavy proton). It is named after Niels Bohr, due to its role in the Bohr model of an atom. Its value is 5.29177210903(80)×10⁻¹¹ m.

Looks like it came from:
https://en.wikipedia.org/wiki/Bohr_radius

So the Wikipedia values are inconsistent by 8×10⁻22 m.

Nobody said wikipedia was perfect unless they said it about their own post.

roughbarked said:

The Rev Dodgson said:

Tamb said:

Note the words most probable
The Bohr radius (a₀) is a physical constant, equal to the most probable distance between the nucleus and the electron in a hydrogen atom in its ground state (non-relativistic and with an infinitely heavy proton). It is named after Niels Bohr, due to its role in the Bohr model of an atom. Its value is 5.29177210903(80)×10⁻¹¹ m.

Looks like it came from:
https://en.wikipedia.org/wiki/Bohr_radius

So the Wikipedia values are inconsistent by 8×10⁻22 m.

Nobody said wikipedia was perfect unless they said it about their own post.

What?

You mean it isn’t The Answer to Everything?

The Rev Dodgson said:

roughbarked said:

The Rev Dodgson said:

Looks like it came from:
https://en.wikipedia.org/wiki/Bohr_radius

So the Wikipedia values are inconsistent by 8×10⁻22 m.

Nobody said wikipedia was perfect unless they said it about their own post.

What?

You mean it isn’t The Answer to Everything?

The Rev Dodgson said:

roughbarked said:

The Rev Dodgson said:

Looks like it came from:
https://en.wikipedia.org/wiki/Bohr_radius

So the Wikipedia values are inconsistent by 8×10⁻22 m.

Nobody said wikipedia was perfect unless they said it about their own post.

What?

You mean it isn’t The Answer to Everything?

]citation required[
fixed.

The Rev Dodgson said:

roughbarked said:

The Rev Dodgson said:

Looks like it came from:
https://en.wikipedia.org/wiki/Bohr_radius

So the Wikipedia values are inconsistent by 8×10⁻22 m.

Nobody said wikipedia was perfect unless they said it about their own post.

What?

You mean it isn’t The Answer to Everything?

Wiki is a self correcting system
knowledge is corrected and added to over time

The (17) is the uncertainty in the last two digits.

5.2917721092(17)×10^-11^ m means between 5.2917721075 ×10^-11^ m and 5.2917721109×10^-11^ m

dv said:

The (17) is the uncertainty in the last two digits.

5.2917721092(17)×10^-11^ m means between 5.2917721075 ×10^-11^ m and 5.2917721109×10^-11^ m

That’s just what btm said.

But thanks anyway :)

btm said:

The Rev Dodgson said:

btm said:

The (17) represents the uncertainty in the last two digits of the value, not additional figures.

So +-17?

No, ±17×10^-21; the last two digits of the value. That means the value is between 5.2917721075×10^-11 and 5.2917721109×10^-11

Thanks. I hadn’t know that. I’ve seen this notation oodles of times (eg. in Handbook of Chemistry and Physics) but never known what it meant.

roughbarked said:

The Rev Dodgson said:

roughbarked said:

Nobody said wikipedia was perfect unless they said it about their own post.

What?

You mean it isn’t The Answer to Everything?

[citation required]