Plank constant

[Jacques]

My question is simple, but I can't find an answer with google or wiki:(

How does Plank found that value ?

[math]h=6.6*10^{-34} J s[/math]

How did he derived it ?

Thanks

[swansont]

It was/is experimentally determined, not derived.

 

http://www.physics.umd.edu/lecdem/services/demos/demosp2/p2-01.htm

http://www.aip.org/pnu/1998/split/pnu391-2.htm

[Jacques]

Thanks for the links.

I can read that h is the slope of the stopping potential as a function of frequency, mutiplied by the electron charge.

h=e(V2-V1)/(f2-f1)

Why does the electron charge putted in the equation ?

 

I tried to check if this expression give the good unit of measure.

 

The unit of V is m2·kg·s-3·A-1

The unit of f is s-1

The unit of e is s·A

so the unit of h is m2·kg·s-1

 

The unit of J is m2·kg·s-2

So the unit of h is J·s or m2·kg·s-1 which is consitent

 

I was surprise to see that ampere (A) was a SI base units. I was expecting something more fundamental like the Coulomb © and that A would be a derived unit C·s-1

[swansont]

Thanks for the links.

I can read that h is the slope of the stopping potential as a function of frequency, mutiplied by the electron charge.

h=e(V2-V1)/(f2-f1)

Why does the electron charge putted in the equation ?

 

Because qV gives you the energy of the electron accelerated through a potential.

[Fred56]

It's a proportionality between two measurable aspects, but which two...

(angular) momentum; wavenumber; frequency; spin; charge? What dimensionality (units)?

[bombus]

The plank constant is the size of pixels in the simulation that we inhabit!