Questions
for Week Two—Spectroscopy and materials
Write
well-reasoned verbal answers to these questions. You should be able to find the
base for your answer in the week’s readings, but the questions are not directly
answered there. You have to think them out, using the facts and concepts from
the reading. Calculations are not necessary, though if you find it useful,
include them by all means. Make sure your prose is clear and complete. One or
two paragraphs should be enough for each question.
(1) High resolution spectroscopy is
carried out in the gas phase, under high vacuum, and at very low
temperature. Explain how each of these
conditions affects resolution.
(2)
The
selection rule for an electronic or vibrational transition is that the molecule
posses a transient dipole moment, but for rotation a permanent dipole is
required. Explain why this is true.
(3)
What does it mean
to say, “At high temperatures, the filament sublimes”?
(4)
Define “p-type”
and “n-type” materials.
(5)
Note 1 of the LED
article mentions weight reduction of vehicles due to the lighter lamp
assemblies and wiring possible with the use of LED’s, and claims that this
reduces fuel use. Make a rough estimate of what percentage reduction in fuel
use one might expect in a typical car or truck from this effect. Assume that
fuel use is proportional to the vehicle’s total weight. The numbers in this
exercise can be very rough; the point is to see whether the effect mentioned is
likely to be big or small. So if you don’t have very exact weights for typical
vehicles, estimate that, too, using rough numbers about the dimensions of the
vehicle, the thickness of steel in various key places, the volume of the engine
block, etc.