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The effect of a cool, dilute gas between an observer and a continuous hot source is that _____.a.)the spectral lines will be broadened by the heat from the sourceb.) dark absorption lines will appear in the spectrumc. )the peak of the continuous spectrum will be shifted toward lower frequenciesd.) the peak of the continuous spectrum will be shifted toward higher frequenciese.) bright emission lines will appear in the spectrum

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Answer:

b.) dark absorption lines will appear in the spectrum.

The effect of a cool, dilute gas between an observer and a continuous hot source is that dark absorption lines will appear in the spectrum.

Explanation:

Kirchhoff’s laws establish that:

  • A solid, liquid or dense incandescent gas emits a continuous spectrum.
  • A hot and diffuse gas produces bright spectral lines (emission lines).
  • A gas of lower temperature against a source of continuum spectrum, produces dark spectral lines (absorption lines) superposed in the continuum spectrum.

Stars are great scenarios to understand Kirchhoff’s laws. Since the spectrum¹ that is received from them will have different features according with the several configuration described above. Stars are not at homogeneous temperature, that leads to gradients in different layers because to its constant exchange of heat with its surroundings in an attempt to reach the thermodynamic equilibrium.

The continuum observed in the stellar spectra comes from the inner layer of the photosphere (higher temperature), while absorption lines are formed in the outer layer of the photosphere and the stellar atmosphere (lower temperature). More accurately, a photon of the inner layer of the photosphere will be absorbed by an electron of an atom or ion that is in the outer layer, generating an electronic transition², the electron, upon returning to its base state will emit a photon or a series of photons that will not necessarily go in the same direction of the incident photon, creating an absorption line in the stellar spectrum.

It is important to remember that photons are the particles that constitute light.

Keys terms:

¹Spectrum: Decomposition of light in its characteristic colors (wavelengths).

²Electronic transition: When an electron passes from one energy level to another, either for the emission or absorption of a photon.

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