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Chapter 20: Q31P (page 527)
Explain how beam chopping reduces line noise and noise from source drift.
The phenomenon of beam chopping line noise and noise from a source drift directed beam is investigated using sample and reference cells.
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What level of stray light gives an absorbance error of 0.01 at an absorbance of 2? That is, what value of Sgives an apparent absorbance of 1.99?
Here is an extremely sensitive method for measuring nitrite () down to in natural waters. The water sample is treated with sulfanilamide and N-(1-naphthylethylenediamine) in acid solution to produce a colored product with a molar absorptivity of at 540 nm. The colored solution is pumped into a 4.5-meter-long, coiled Teflon tube whose fluorocarbon wall has a refractive index of 1.29. The aqueous solution inside the tube has a refractive index near 1.33. The colored solution is pumped through the coiled tube. An optical fiber delivers white light into one end of the tube, and an optical fiber at the other end leads to a polychromator and detector.
(a) Explain the purpose of the coiled Teflon tube and explain how it functions.
(b) What is the critical angle of incidence for total internal reflection at the Teflon/water interface?
(c) What is the predicted absorbance of a solution of colored reagent?
The exitance (power per unit area per unit wavelength) from a blackbody (Box 20-1) is given by the Planck distribution: where is wavelength, Tis temperature K), his Planck鈥檚 constant, Cis the speed of light, and kis Boltzmann鈥檚 constant. The area under each curve between two wavelengths in the blackbody graph in Box 20-1is equal to the power per unit areaemitted between those two wavelengths. We find the area by integrating the Planck function between wavelengthsand
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For a narrow wavelength range, the value of is nearly constant and the power emitted is simply the product .
(a) Evaluate and at
(b) Calculate the power emitted per square meter atin the intervalby evaluating the product
(c) Repeat part (b) for the interval
(d) The quantityis the relative exitance at the two wavelengths. Compare the relative exitance at these two wave-lengths atwith the relative exitance at 100K. What does your answer mean?
The prism shown here is used to totally reflect light at aangle. No surface of this prism is silvered. Use Snell's law to explain why total reflection occurs. What is the minimum refractive index of the prism for total reflection?
What are the advantages and disadvantages of decreasing monochromator slit width?
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