In comparing photons of different wavelengths, we find that the energy carried by a photon
is larger if the wavelength is shorter.
In what way does a photon of blue light not differ from a photon of yellow light in a vacuum?
The energy of a photon of X-rays, compared to the energy of a photon of visible light, is
An electron volt (eV) is a unit of
Spectral lines are of particular importance in astronomy because
each different element has a characteristic line spectrum.
Atoms in a hot, low-density gas (e.g., in a laboratory-type spectral source) emit a spectrum that is
a series of specific colors, unique to the type of atom in the tube, but fixed in position even when the gas temperature changes.
The gas in interstellar space between the stars is very tenuous (“thin”). Near a hot star, this gas is heated to a high temperature. Any such hot, tenuous gas emits light
only at specific wavelengths (“spectral lines”), and these spectral lines do not change in wavelength as the temperature changes.
The chemical makeup of a star's surface is obtained by
spectroscopy of the light emitted by the star.
If a certain gas is heated and observed through a grating, a bright line spectrum will be seen. If instead, a source of continuous spectrum shines through a cooler sample of this same gas, a dark absorption spectrum is observed. How do the positions of the lines in these two spectra compare?
The lines in the two spectra will be at the same frequencies. They will be the same spectra.
Chemical pollution often results in large numbers of very small particles being emitted into the atmosphere. What effect, if any, will this have on the color of the sunset?
It should make the sunset look more red.
The physical structure of an atom is
negatively charged electrons moving around a very small but massive, positively charged core.
The overall diameter of a typical atom is about
10^–10 m, or 0.1 nm.
The New Zealand physicist Lord Rutherford and his colleagues in England demonstrated the existence of the very small but massive nucleus inside every atom in which crucial experiment?
deflection, and occasional reflection backward, of energetic nuclear particles from a beam aimed at a thin metal sheet
Most of the mass of ordinary matter resides in the
nuclei of atoms.
The diameter of the nucleus of a typical atom (as measured by Rutherford in the early 1900s) is
10^–4 of the diameter of the atom.
The atomic number that designates the position of an element in the periodic table is equal to the
number of protons in the nucleus of the atom.
Isotopes of a particular element in the periodic table have which nuclear property in common?
same number of protons but different numbers of neutrons
The isotope 15N has an atomic number of 7. This isotope has
7 protons and 8 neutrons.
The specific colors of light emitted by an atom in a hot, thin gas (e.g., in a tube in a laboratory or a gas cloud in space) are caused by
electrons jumping to lower energy levels, losing energy as they do so.
When astronomers look for evidence of hydrogen gas in the spectra of the Sun, the planets, and nearby stars, the positions of the spectral features or “lines” due to hydrogen
are always in the same pattern, characteristic of hydrogen gas, as seen in the laboratory.
Electrons in atoms
occupy levels whose energies are fixed.
Ionization of an atom occurs when
an electron is removed from the atom.
An ionized hydrogen atom is simply
The observed change in wavelength due to the Doppler effect occurs
only when the light source has a radial velocity (toward or away from the observer).
The spectrum of a star shows an equivalent set of dark absorption lines to those of the Sun, but with one exception: Every line appears at a slightly longer wavelength, shifted toward the red end of the spectrum. What conclusion can be drawn from this observation?
The star is moving rapidly away from Earth.
An astronomer photographs the spectrum of an object and finds a spectral line at 499 nm wavelength. In the laboratory, this spectral line occurs at 500 nm. According to the Doppler effect, this object is moving
toward Earth at 1/500 the speed of light.
A star looks predominantly yellow to an observer who is at rest with respect to the star. To an observer moving away from the star at 1% of the speed of light
the star will still look predominantly yellow, but each part of the spectrum will be shifted to slightly longer wavelengths.
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