Undergrad Atomic Layers calculation in Feynman lectures

[Aleoa]

The lecture is here, paragraph 5-7.

Feynman is trying to explain how to measure the size of the nucleus.

He writes :

"Suppose we have a piece of material
1 centimeter thick. There will be about 10^8 atomic layers.

Since we don't know the size of the nucleous, how can be possible to calculate how many atomic layers are situated in 1 centimer of a (unspecified) material ?

 

[Vanadium 50]

The answer is given in the first two paragraphs of the very same section.

 

[Aleoa]

The answer is given in the first two paragraphs of the very same section.

\Delta x = v\Delta t ?

 

[Vanadium 50]

Δx=vΔt\Delta x = v\Delta t ?

Appears exactly nowhere in the first two paragraphs of 5.7.

 

[Aleoa]

I think this part:
"First, from an observation of the way light of short wavelength (x-radiation) is reflected from a pattern of marks of known separation, we determine the wavelength of the light vibrations. Then, from the pattern of the scattering of the same light from a crystal, we can determine the relative location of the atoms in the crystal, obtaining results which agree with the atomic spacings also determined by chemical means. We find in this way that atoms have a diameter of about 10−10" role="presentation">10−10 meter."

Unfortunately, i don't understand it , neither intuitively :(

 

[jtbell]

Since we don't know the size of the nucleous, how can be possible to calculate how many atomic layers are situated in 1 centimer of a (unspecified) material ?

The number of atomic layers is related to the size of the entire atom, not the size of the nucleus. The size of atoms can be determined e.g. by methods that Feynman describes in the paragraph immediately following Fig. 5-9 (which I now see you've quoted above). That method uses the concept of diffraction gratings, which you can read about in Chapter 30.

Another method is to use the material's "atomic weight" (g/mole), Avogadro's number (atoms/mole) and the material's density (g/cm³) to arrive at the volume per atom. This is basically the "chemical means" that Feynman referred to.