Jump to content


Photo
- - - - -

Plank's Constant for laymen.


  • Please log in to reply
15 replies to this topic

#1 Gareth56

Gareth56

    Atom

  • Senior Members
  • 271 posts

Posted 8 February 2008 - 02:54 PM

If a layman were to ask what is Planck's Constant and what does the figure 6.626 x10^-34 Js mean how could you describe what it means?
  • 0

#2 swansont

swansont

    Shaken, not stirred

  • Moderators
  • 27,303 posts
  • LocationWashington DC region

Posted 8 February 2008 - 03:10 PM

A very small layman? :-)

It's the quantum of angular momentum in quantum physics; all changes in angular momentum come in steps no smaller than this.

It's also the conversion factor from frequency to energy.
  • 0

Minutus cantorum, minutus balorum, minutus carborata descendum pantorum                                   To shake my vodka martini, click the up arrow ^

I am not a minimum-wage government shill.             Forget it, Jake — it's Crackpottown.

My SFN blog: Swans on Tea                                                           

 

 

                                                                                                                     

 

 


#3 Gareth56

Gareth56

    Atom

  • Senior Members
  • 271 posts

Posted 8 February 2008 - 03:14 PM

Thanks but sadly our layman is just looking at you with a very very blank expression :doh:
  • 0

#4 swansont

swansont

    Shaken, not stirred

  • Moderators
  • 27,303 posts
  • LocationWashington DC region

Posted 8 February 2008 - 03:46 PM

Things at the quantum level behave like they spin. If the spin vector is pointed in one particular direction, or has a particular magnitude, it can't smoothy change to another value.

It would be as if a motor could only go at 100 rpm, 200 rpm or 300 rpm, etc. but no value in between, or could only be aligned in a limited number of directions.

Planck's constant would be the equivalent of the 100 rpm increment. Except the "spinning" isn't a physical object actually spinning. (QM is quite weird)

This also applies to things behaving like they orbit, except in QM they don't really orbit like a planet orbits. You simply wouldn't be allowed to have a planet in any old orbit. Mars is OK, Earth is OK, but the spaceship orbit getting from one to the other isn't permitted.
  • 0

Minutus cantorum, minutus balorum, minutus carborata descendum pantorum                                   To shake my vodka martini, click the up arrow ^

I am not a minimum-wage government shill.             Forget it, Jake — it's Crackpottown.

My SFN blog: Swans on Tea                                                           

 

 

                                                                                                                     

 

 


#5 Gareth56

Gareth56

    Atom

  • Senior Members
  • 271 posts

Posted 8 February 2008 - 04:33 PM

OK, mist is beginning to lift :-)

So what do the units Js mean? I can fully understand what miles per hour or meters per second means but 'Joules second' is a tad mysterious.
  • 0

#6 Martin

Martin

    Physics Expert

  • Resident Experts
  • 4,596 posts
  • LocationSF Bay Area

Posted 8 February 2008 - 05:06 PM

OK, mist is beginning to lift :-)

So what do the units Js mean? I can fully understand what miles per hour or meters per second means but 'Joules second' is a tad mysterious.


Swansont has mentioned angular momentum several times, rotational momentum. Think about what combination of basic units would be appropriate to measure THAT and you will see that Js is a handy concise way of expressing it.

Ordinary linear momentum is measured in kg m/s
and the rotational momentum just equals that multiplied by the radius or lever arm, so kg m2/s

For example think of a half-meter radius wheel with lightweight axle and spokes and a massive 10 kg rim that is going 3 m/s at the rim. so there is 30 kg m/s of ordinary linear momentum, concentrated out at a radial distance of 1/2 meter. both factors, the rim's linear momentum and the radius, contribute to the angular momentum. So you multiply them and get
15 kg m2/s

But if you write a Joule in basic terms, it is just kg m2/s2. That is essentially just the definition of Joule. So multiplying by s
gets you Js as a nice concise way of writing the unit of angular momentum.
===============

there are other ways to think about it, like the Joule is also the unit of torque----"twist force"-----and the angular momentum you put on freely rotating body like a wheel is proportional to the torque you apply multiplied by the the length of time you apply it
  • 0
Loll quantum gravity SciAm
http://www.signallak...uantumJul08.pdf
cosmology SciAm
www.mso.anu.edu.au/~charley/papers/LineweaverDavisSciAm.pdf
http://www.einstein-...logy/index.html

#7 swansont

swansont

    Shaken, not stirred

  • Moderators
  • 27,303 posts
  • LocationWashington DC region

Posted 8 February 2008 - 05:10 PM

OK, mist is beginning to lift :-)

So what do the units Js mean? I can fully understand what miles per hour or meters per second means but 'Joules second' is a tad mysterious.


The amount of angular momentum is the linear momentum multiplied by the moment arm length (and a trig function if those aren't perpendicular). Linear momentum is mv, or kg-m/s, and multiply by the moment arm (m) to get kg-m^2/s. Well, a kg-m/s^2 is a Newton (force = ma) and a kg-m^2/s^2 is a Joule (work or energy)

So a kg-m^2/s is a J-s

Angular momentum (L) is also related to torque (T), T = dL/dt which gets you to the same point

(it can be misleading that torque and energy have the same units, because energy does not always involve rotation, so this unit analysis isn't generally used for macroscopic objects. Torque is usually left as N-m rather than represented as a Joule)
  • 0

Minutus cantorum, minutus balorum, minutus carborata descendum pantorum                                   To shake my vodka martini, click the up arrow ^

I am not a minimum-wage government shill.             Forget it, Jake — it's Crackpottown.

My SFN blog: Swans on Tea                                                           

 

 

                                                                                                                     

 

 


#8 bombus

bombus

    Molecule

  • Senior Members
  • 759 posts
  • LocationGogledd Cymru (North Wales)

Posted 8 February 2008 - 08:06 PM

It is the measure of the minimum 'grainyness' of the universe. It is the resolution of reality. Think of pixels on this computer screen. The plank constant is the minimum size of the pixels in our universe.

Is that lay enough?
  • 0
Never ever bloody anything ever!

#9 swansont

swansont

    Shaken, not stirred

  • Moderators
  • 27,303 posts
  • LocationWashington DC region

Posted 8 February 2008 - 09:27 PM

It is the measure of the minimum 'grainyness' of the universe. It is the resolution of reality. Think of pixels on this computer screen. The plank constant is the minimum size of the pixels in our universe.

Is that lay enough?


You may be confusing the planck length with planck's constant. (the former being the scale where you'd need a quantum theory of gravity because general relativity breaks down)
  • 0

Minutus cantorum, minutus balorum, minutus carborata descendum pantorum                                   To shake my vodka martini, click the up arrow ^

I am not a minimum-wage government shill.             Forget it, Jake — it's Crackpottown.

My SFN blog: Swans on Tea                                                           

 

 

                                                                                                                     

 

 


#10 bombus

bombus

    Molecule

  • Senior Members
  • 759 posts
  • LocationGogledd Cymru (North Wales)

Posted 9 February 2008 - 09:42 PM

You may be confusing the planck length with planck's constant. (the former being the scale where you'd need a quantum theory of gravity because general relativity breaks down)


I thought the plank constant was the mathematical function used to account for the plank length when attempting calculations regarding the sub-atomic realm.
  • 0
Never ever bloody anything ever!

#11 swansont

swansont

    Shaken, not stirred

  • Moderators
  • 27,303 posts
  • LocationWashington DC region

Posted 9 February 2008 - 11:29 PM

I thought the plank constant was the mathematical function used to account for the plank length when attempting calculations regarding the sub-atomic realm.


Planck's constant is one of the terms in the Planck length, but they aren't the same thing. The different units tell you that some other terms must be involved, and in the case of the Planck length G is involved (which is small), and so is c (in the denominator, cubed) which makes the terms smaller still.
  • 0

Minutus cantorum, minutus balorum, minutus carborata descendum pantorum                                   To shake my vodka martini, click the up arrow ^

I am not a minimum-wage government shill.             Forget it, Jake — it's Crackpottown.

My SFN blog: Swans on Tea                                                           

 

 

                                                                                                                     

 

 


#12 elas

elas

    Molecule

  • Senior Members
  • 628 posts

Posted 10 February 2008 - 08:30 PM

swansont

Except the "spinning" isn't a physical object actually spinning. (QM is quite weird)

How do you explain the anomalous magnetic moment if the particle does not spin?
  • 0

#13 Klaynos

Klaynos

    Insert Witty Comment

  • Moderators
  • 7,447 posts

Posted 10 February 2008 - 09:05 PM

swansont

Except the "spinning" isn't a physical object actually spinning. (QM is quite weird)

How do you explain the anomalous magnetic moment if the particle does not spin?


http://en.wikipedia....nt_of_electrons

No one said they didn't have angular momentum.
  • 0
Klaynos - share and enjoy.

#14 swansont

swansont

    Shaken, not stirred

  • Moderators
  • 27,303 posts
  • LocationWashington DC region

Posted 10 February 2008 - 11:11 PM

It's a QED correction

http://en.wikipedia....c_dipole_moment

(if course, this link is contained in the one Klaynos gave)
  • 0

Minutus cantorum, minutus balorum, minutus carborata descendum pantorum                                   To shake my vodka martini, click the up arrow ^

I am not a minimum-wage government shill.             Forget it, Jake — it's Crackpottown.

My SFN blog: Swans on Tea                                                           

 

 

                                                                                                                     

 

 


#15 elas

elas

    Molecule

  • Senior Members
  • 628 posts

Posted 11 February 2008 - 07:11 AM

PHILOSOPHY AND YOUR RANDOM THOUGHTS ARE NOT SCIENCE DO NOT POST THEM AS SUCH

One could reply that it is equally true to say that mathematical prediction is not science but, such comments are not really helpful. Instead I would point out that there is an alternative view derived from Stochastic Electrodynamics. The crux of the debate is exactly what should be included within the particle, and what should be considered as part, or all; of some external field. Mac Gregor lays out the case in 'The Enigmatic Electron' If the magnetic field of a particle is within the particle then the four different electron radii (as explained by Mac Gregor) can be shown to be distinct parts of a vacuum/anti-vacuum field.
  • 0

#16 1eyedjack

1eyedjack

    Lepton

  • Members
  • 4 posts

Posted 4 August 2008 - 08:58 PM

If anyone asks me a question how to explain a quantum physics phenomenon to a layman I direct him to read Mr Tomkins in Paperback, by George Gamow. I certainly couldn't explain it better than he.
  • 0




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users