Planck's constant

[Chriss]

Why has the Planck's constant has a value of 6.62606957 × 10⁻³⁴ joule∙second, and a standard uncertainty of 0.00000029 × 10⁻³⁴ joule∙second ?

 

Explain me the uncertainty.

Edited February 19, 2016 by Chriss

[Klaynos]

Limits of experimental precision...

[swansont]

Why has the Planck's constant has a value of 6.62606957 × 10⁻³⁴ joule∙second, and a standard uncertainty of 0.00000029 × 10⁻³⁴ joule∙second ?

 

Explain me the uncertainty.

 

All measurements have uncertainty; there is no such thing as an infinitely precise measurement.

[Sensei]

Why has the Planck's constant has a value of 6.62606957 × 10⁻³⁴ joule∙second,

AFAIK current value is 6.62607004*10^-34 J*s

 

and a standard uncertainty of 0.00000029 × 10⁻³⁴ joule∙second ?

 

Explain me the uncertainty.

It's normal practice.

Wikipedia is your friend:

https://en.wikipedia.org/wiki/Measurement_uncertainty

https://en.wikipedia.org/wiki/Accuracy_and_precision

 

 

Even if you measure mass on weight, it has mentioned +- some tolerance in reading. f.e. my weight has +-0.01 g.

Typical chemistry lab graduated cylinder has +-1 mL tolerance.

While calculating density of liquid (m/V), you would have to take both +- tolerance of mass and volume into account,

and calculate how precisely you can have density calculated..

Edited February 19, 2016 by Sensei

[Chriss]

Does static electricity have an uncertainty in measurement?

[John Cuthber]

Does static electricity have an uncertainty in measurement?

Yes- generally rather a large one.

[ajb]

Does static electricity have an uncertainty in measurement?

You are phrasing this very strangely.

 

 

All experiments have uncertainty in all measurements they make.

[EdEarl]

As a naked ape, nothing about our body lets measure anything exactly. Everything about your body is unique, including legs, eyes, and hair, until we look at subatomic particles. It is possible some electrons are identical to one another, but we cannot measure accurately enough to know.

 

To make a measurement, we compare two things, for example a standard meter with something we think is also a meter, but we cannot know they are exactly the same length, because there are limits on how small a difference we can see, even with a microscope. The same principle applies for all measurements and instruments (e.g., microscope) that aid making measurements.

Edited February 20, 2016 by EdEarl

[Klaynos]

I like this book on the subject:

 

http://www.amazon.com/Introduction-Error-Analysis-Uncertainties-Measurements/dp/093570275X

 

John R. Taylor, An Introduction to Error Analysis: The Study of Uncertainties in Physical Measurements

[swansont]

As a naked ape, nothing about our body lets measure anything exactly. Everything about your body is unique, including legs, eyes, and hair, until we look at subatomic particles. It is possible some electrons are identical to one another, but we cannot measure accurately enough to know.

 

To make a measurement, we compare two things, for example a standard meter with something we think is also a meter, but we cannot know they are exactly the same length, because there are limits on how small a difference we can see, even with a microscope. The same principle applies for all measurements and instruments (e.g., microscope) that aid making measurements.

 

Two things:

 

1. Some of the limitations having nothing to do with being naked apes. Nature is inherently noisy.

 

2. We can show that electrons are identical. The Pauli exclusion principle depends on it. Atoms (as described by QM) exist, thus electrons are identical particles, unless you are willing to justify tossing out QM.

[EdEarl]

 

Two things:

 

1. Some of the limitations having nothing to do with being naked apes. Nature is inherently noisy.

 

2. We can show that electrons are identical. The Pauli exclusion principle depends on it. Atoms (as described by QM) exist, thus electrons are identical particles, unless you are willing to justify tossing out QM.

When an electron absorbs a photon and jumps to a higher energy level around an atom, has it not changed? Moreover, the field shape of various electrons within an atom are different.

 

Two things:

 

1. Some of the limitations having nothing to do with being naked apes. Nature is inherently noisy.

 

2. We can show that electrons are identical. The Pauli exclusion principle depends on it. Atoms (as described by QM) exist, thus electrons are identical particles, unless you are willing to justify tossing out QM.

When an electron absorbs energy from a photon it has changed, has it not? And, we don't actually know what an electron is, we cannot see that detail. I believe the nucleus of an atom, e.g., hydrogen, has quark-antiquark pairs popping into existence and annihilating quickly, but they contribute mass. Is that the case within electrons?

Edited February 20, 2016 by EdEarl

[swansont]

When an electron absorbs a photon and jumps to a higher energy level around an atom, has it not changed? Moreover, the field shape of various electrons within an atom are different.

 

When an electron absorbs energy from a photon it has changed, has it not? And, we don't actually know what an electron is, we cannot see that detail. I believe the nucleus of an atom, e.g., hydrogen, has quark-antiquark pairs popping into existence and annihilating quickly, but they contribute mass. Is that the case within electrons?

Same (identical) electron, different state. If electrons were not identical, they could all occupy a single energy and spin state.

 

Electrons have no internal structure.

[Sensei]

Same (identical) electron, different state. If electrons were not identical, they could all occupy a single energy and spin state.

 

Now, you're talking about "placement" of electrons inside of single atom/molecule.. While EdEarl started with particles of f.e. gas at different altitudes.

 

While making experiment in quantum physics typically there are used f.e. highly accelerated electrons to ionize medium, which can be gas such as Hydrogen.

When electrons/atoms come back to their ground state, they emit photons, that are split on prism, and analyzed as spectral lines.

 

Other example: vacuum tube, with two electrodes, and some metal between them,

electrons are emitted, and accelerated in electric field between electrodes, hit metal (or other solid) piece between them, and there are produced x-rays.

With peaks were are ionization energies of electrons of this metal.

 

But all this does not include gravity into account!

In classic physics object that is at higher altitude than other object, has slightly different, higher energy.

In other words: particle at 1 nm above other particle has slightly higher energy. With plentiful of such particles it gives rise to E=mgh

Substitute m by mass of proton m_p, or mass of electron m_e, and h by some 1 nm, 1 pm, or 1 fm... And they are not equal, when we take gravity into account.

This difference in energy is so meaningless small that it's way below precision of QM measurements (which are done in high ionization energies, in plasma state).

 

Electrons have no internal structure.

"Electrons have no internal structure according to currently known main stream physics",

is not the same as

"Electrons have no internal structure" (in absolute knowledge).

 

At the time Schrodinger was working on his equation, there were known only electron, photon and proton.

So I assume, early XX century physicians took as granted that proton is elementary particle, without internal structure, as well.

 

One could ask what is difference in electrons, one with 1 eV kinetic energy, other one with 1 keV kinetic energy, and another one with 1 MeV kinetic energy...

The first one after hitting material could not ionize anything, as it's too low energy, no trace in Cloud Chamber,

The second one after hitting material could ionize plentiful of particles, tiny (probably barely visible) trace in Cloud Chamber,

The third one will have the greatest impact from all three.. Large eye visible trace in Cloud Chamber.

Edited February 20, 2016 by Sensei

[swansont]

Now, you're talking about "placement" of electrons inside of single atom/molecule.. While EdEarl started with particles of f.e. gas at different altitudes.

 

No. I can't find where he said anything about a free electron gas. He said "an electron absorbs a photon and jumps to a higher energy level around an atom" so the rest of your example is beside the point. It's also moot, because an atom is sufficient to show that electrons are identical particles, as I already pointed out. The reason they have the structure they do is because of the Pauli exclusion principle. If they were not identical, they would be free to all drop into the ground state.

 

"Electrons have no internal structure according to currently known main stream physics",

is not the same as

"Electrons have no internal structure" (in absolute knowledge).

Any statements made in such a context always carries with it the caveat "according to what we currently know". It's implied.

[John Cuthber]

 

"Electrons have no internal structure according to currently known main stream physics",

is not the same as

"Electrons have no internal structure" (in absolute knowledge).

 

Where on that scale does "We have looked for evidence of an internal structure of the electron, but so far we have no found any." fall?

 

On a related note, what about these statements

"My bedroom contains no tigers according to currently known mainstream physics.

"My bedroom contains no tigers"

and

"I have looked for tigers in my bedroom and found none".

 

The real question is, do I need to take a gun to bed with me, and the answer in all three cases is "no".

 

Perhaps we can get back to the topic now (assuming that Chriss tells us what that actually is).

[Chriss]

If I want to measure the van der waals forces of what should I use ?

[Strange]

If I want to measure the van der waals forces of what should I use ?

 

 

Apparently, an atomic force microscope: https://phys.org/news/2016-05-physicists-van-der-waals-individual.html