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Chapter 20: Q3P (page 525)
Would you use a tungsten or a deuterium lamp as a source of 300-nm radiation? What kind of lamp provides radiation at 4-mm wavelength?
We would use a deuterium lamp as a source of 300-nm radiation.
Silicon carbide globar lamp provides radiation at wavelength.
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The true absorbance of a sample is 1.000, but the mono chromator passes 1.0% stray light. Add the light coming through the sample to the stray light to find the apparent transmittance of the sample. Convert this answer back into absorbance and find the relative error in the calculated concentration of the sample.
In Figure 20-35, the relative detection limit is 37 after 1sof signal averaging, 12.5 after 10s, and 5.6 after 40 sof signal averaging. Based on the value of 37 at 1 s, what are the expected detection limits at 10 sand 40 sin an ideal experiment?
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 measurement with a signal-to-noise ratio of 100 / 1 can be thought of as a signal, S, with 1 % uncertainty, e. That is, the measurement is.
(a) Use the rules for propagation of uncertainty to show that, if you add two such signals, the result is total signal , giving a signal-to-noise ratio of .
(b) Show that if you add four such measurements, the signal-tonoise ratio increases to 200 / 1.
(c) Show that averaging n measurements increases the signal-to-noise ratio by a factor of compared with the value for one measurement.
Explain how beam chopping reduces line noise and noise from source drift.
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