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Chapter 20: Q18P (page 526)
Explain how an optical fibre works. Why does the fibre still work when it is bent?
When the fibre is bent, theangle exceeds the critical angle, preventing light from leaving the core.
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Results of an electrochemical experiment are shown in the figure. In each case, a voltage is applied between two electrodes at timeand the absorbance of a solution decreases until the voltage is stepped back to its initial value at time. The upper traces show the average results for 100,300, and 1000 repetitions of the experiment. The measured signal-to-rms noise ratio in the upper trace is 60.0. Predict the signal-to-noise ratios expected for 300 cycles, 100 cycles, and 1 cycle and compare your answers with the observed values in the figure.
(a) In the cavity ring-down measurement at the opening of this chapter, absorbance is given by whereis the length of the triangular path in the cavity, Cis the speed of light, Tis the ring-down lifetime with sample in the cavity, and is the ring-down lifetime with no sample in the cavity. Ring-down lifetime is obtained by fitting the observed ring-down signal intensityto an exponential decay of the form , whereis the initial intensity and t is time. A measurement ofis made at a wavelength absorbed by the molecule. The ring-down lifetime for 21.0-cm-1 along empty cavity is andfor a cavity containing.role="math" localid="1664865078479" Find the absorbance ofat this wavelength.
(b) The ring-down spectrum below arises from and from of methane in outdoor air at 0.13. The spectrum arises from individual rotational transitions of the ground vibrational state to a second excited C-H)vibrational state of the molecule. (i) Explain what quantity is plotted on the ordinate ( Y-axis). (ii) The peak foris at. What is the wavelength of this peak in? What is the name of the spectral region where this peak is found?
Visible light strikes the surface of benzene at a angle. At what angle does the light ray pass through the benzene?
A spectrum has a signal-to-noise ratio of 8/1. How many spectra must be averaged to increase the signal-to-noise ratio to 20 / 1?
Find the minimum anglefor total reflection in the optical fiber in Figure 20-21 if the index of refraction of the cladding is 1.400 and the index of refraction of the core is
(a) 1.600 or
(b) 1.800.
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