A spectroscope prism separates the white light from a star into a very wide spectrum. When widely spread, black lines appear in the spectrum. Particular elements in a star create specific patterns in the lines. What can you conclude about a spectroscope from this passage?

a
It allows scientists to determine a star's evolutionary stage.
b
It helps scientists measure a star's mass.
c
It helps scientists detect dark matter.
d
It allows scientists to determine which elements are present in a star.

Which diagram correctly demonstrates the various forces acting on a ball moving horizontally with some speed?

Some material consisting of a collection of microscopic objects is kept at a high temperature. a photon detector capable of detecting photon energies from infrared through ultraviolet observes photons emitted with energies of 0.3 ev, 0.5 ev, 0.8 ev, 2.0ev, 2.5ev, and 2.8ev. these are the only photon energies observed. (a) draw and label a possible energy-level diagram for one of the microscopic objects, which has four bound states. on the diagram, indicate the transitions corresponding to the emitted photons. explain briefly. (b) would a spring–mass model be a good model for these microscopic objects? why or why not? (c) the material is now cooled down to a very low temperature, and the photon detector stops detecting photon emissions. next, a beam of light with a continuous range of energies from infrared through ultraviolet shines on the material, and the photon detector observes the beam of light after it passes through the material. what photon energies in this beam of light are observed to be significantly reduced in intensity (“dark absorption lines”)? explain briefly.

Glass has a hardness that is in the middle of the hardness scale. what is the hardness of glass?