The inner and outer surfaces of a 25-cm-thick wall in summer are at 27 °c and 44 °c, respectively. the outer surface of the wall exchanges heat by radiation with surrounding surfaces at 40 °c, and convection with ambient air also at 40 °c with a convection heat transfer coefficient of 8 w/m2°c. solar radiation is incident on the surface at a rate of 150 w/m2. if both the emissivity and the solar absorptivity of the outer surface are 0.8, determine the effective thermal conductivity of the wall

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.