Atomic Layers calculation in Feynman lectures

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Discussion Overview

The discussion revolves around the calculation of atomic layers in a material as presented in Feynman's lectures, specifically focusing on the relationship between atomic size and the number of atomic layers in a given thickness of material. Participants explore the methods for determining atomic dimensions and the implications of these measurements.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions how to calculate the number of atomic layers in 1 centimeter of material without knowing the size of the nucleus.
  • Another participant suggests that the answer is found in the first two paragraphs of the relevant section, implying that it is straightforward.
  • A different participant challenges the relevance of the equation Δx = vΔt in this context, stating it does not appear in the specified paragraphs.
  • One participant expresses confusion over Feynman's explanation regarding the determination of atomic size through light reflection and scattering, indicating a lack of intuitive understanding.
  • Another participant clarifies that the number of atomic layers relates to the size of the entire atom rather than the nucleus, mentioning methods such as diffraction gratings and chemical means to determine atomic size.
  • It is noted that using atomic weight, Avogadro's number, and density can help calculate the volume per atom, which is relevant to understanding atomic layers.

Areas of Agreement / Disagreement

Participants express differing levels of understanding regarding Feynman's explanation and the methods for calculating atomic layers. There is no consensus on the clarity of the material or the applicability of the proposed methods.

Contextual Notes

Some assumptions about the definitions of atomic size and the methods for measurement are not fully explored, leading to potential gaps in understanding. The discussion also highlights the dependence on specific sections of Feynman's text, which may not be universally interpreted.

Aleoa
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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 ?
 
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The answer is given in the first two paragraphs of the very same section.
 
Vanadium 50 said:
The answer is given in the first two paragraphs of the very same section.

\Delta x = v\Delta t ?
 
Aleoa said:
Δx=vΔt\Delta x = v\Delta t ?

Appears exactly nowhere in the first two paragraphs of 5.7.
 
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 :(
 
Aleoa said:
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.
 
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