Help w/ physics gre problem: radiation spectra

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Discussion Overview

The discussion revolves around a physics GRE problem related to radiation spectra, specifically evaluating the correctness of various statements about electromagnetic radiation and its implications for understanding atomic and molecular structures. The scope includes conceptual clarification and technical reasoning regarding absorption and emission spectra.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Post 1 presents a question about which statement regarding radiation spectra is incorrect, suggesting that answer 'a' is the false one.
  • Post 2 reiterates the belief that if 'a' is false, then the other statements must be true.
  • Post 3 supports the assertion that 'a' is false, referencing the shell model of the nucleus and the energy levels of nucleons, which differ significantly from those of electrons.
  • Post 4 elaborates on why 'a' is incorrect, emphasizing that the electromagnetic spectrum in the infrared, visible, and ultraviolet regions is associated with electron transitions rather than nuclear structure, and confirms the truth of the other statements.
  • Post 5 expresses gratitude for the discussion and reflects on the simplicity of the question in hindsight.

Areas of Agreement / Disagreement

Participants generally agree that statement 'a' is incorrect and that the other statements are true, although the reasoning behind these assertions is discussed and elaborated upon.

Contextual Notes

Some participants reference the shell model and energy levels, but there may be assumptions regarding the definitions of terms like "nuclear structure" and "band spectra" that are not fully explored. The discussion does not resolve all potential ambiguities in the statements.

yxgao
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64. Electromagnetic radiation provides a means to probe aspects of the physical universe. Which of the following statements regarding radiation spectra is NOT correct?

a. lines in the infaret, visible, and ultraviolet regions of the spectrum reveal primarily the nuclear structure of the sample.
b. the wavelengths identified in an absorption spectrum of an element are among those in its emission spectrum.
c. absorption spectra can be used to determine which elements are present in distant stars.
d. spectral analysis can be used to identify the composition of galactic dust.
e. band spectra are due to molecules.

The answer is a. This makes sense to me, but I'm not sure exactly why it must be the correct answer, and the others answers are false. Can someone explain each one in some detail?

Thanks!
 
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yxgao said:
This makes sense to me, but I'm not sure exactly why it must be right, and the others are false.

According to the question, if a is the answer then it must be false and the others are true.
 
Nylex said:
According to the question, if a is the answer then it must be false and the others are true.

Yes,Nylex is right,answer a) is the false one.According to the shell model of the nucleus,nucleons are disposed in energy levels,similar to electrons in the entire atom,but the main difference is that the gaps between successive energy levels is huge,in the order of MeV,so that should take the emission/absorption spectrum to the lower (wavelength) X rays and definitely gamma.

Daniel.

PS.And beside,all of the other answers are true... :-p
 
The key to why answer 'a' is wrong is found in " infared, visible, and ultraviolet regions of the spectrum" and "nuclear structure ".

The electromagnetic spectrum in this range is due to emission from 'atoms', or more specifically the change of state of 'electrons', which orbit the nucleus. They tell nothing of the nuclear structure.

b. is true - An atom will absorb light that is characteristic of its emission spectrum.

c. is true - since b is true.

d. is true - follows from 'c' and 'b'.

e. is true - band spectra
The combination of many different spectral lines resulting from vibrational, rotational and electronic transitions. Unresolved band spectra may appear as a spectral continuum. (from IIUPAC Compendium of Chemical Terminology)
 
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Thanks a lot guys! I suppose that this was a rather simple question, looking back on it.
 

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