Exam 21: Spectrophotometers

Which statement(s)is(are)true for photomultiplier tubes? I Photomultiplier tubes are very sensitive detectors,amplifying the photoelectron current by approximately 1 million. II Emitted photoelectrons are accelerated toward positively charged electrodes called dynodes. III Electrons strike the dynode with a kinetic energy less than the original emitted kinetic energy. IV For each electron striking a dynode,more than one electron is knocked free.The additional electrons are accelerated toward the next dynode in the detector where amplification is repeated.

____________________ response is a function of incident light and produce an electrical current when struck by .For a given radiant power,current is____________________ analyte concentration.

The monochromator for a new instrument design must successfully resolve 0.005 nm at 631 nm.Calculate the minimum number of grooves per centimeter for the diffraction grating if the grating has a length of 5 cm.Assume first order diffraction.

Calculate the minimum grating length to successfully resolve 616.50 nm from 616.59 nm for first-order diffraction.The available diffraction grating is 10³ grooves per cm.

There are many types of noise.Of the noise types below,which is NOT correctly defined?

The true absorbance for a 1.0 x 10⁻⁵ M solution is 0.7526.If the percentage stray light for a spectrophotometer is 0.56%,calculate the percentage by which the apparent concentration deviates from the known concentration.

Which statements are true for optical fibers? I Optical fibers carry light by total internal refraction. II Optical fibers are constructed of a high-refractive-index transparent core enclosed in a lower refractive-index transparent cladding. III Optical fibers exploit Snells Law,n₁ sin ₁ = n₂ sin ₂,to transmit light along the length of the optical fiber. IV If n₁/n₂ < 1,there is an allowed range of angles _i in which essentially all light is reflected at the walls of the core,with negligible amounts of light penetrating the cladding.

Which property of noise does signal averaging exploit to improve the signal-to-noise ratio?

Spectrophotometers employ various sources of light.Which of the following is NOT true for spectrophotometer light sources?

Which property of laser light is NOT correctly defined/described?

Stray light is a problem for spectrophotometers that are not tightly sealed.What is the impact of stray light on the recorded absorbance?

Ni emits light at 345.85 nm and 346.17 nm in an atomic emission spectrophotometer.Can the spectrophotometer's monochromator successfully resolve 345.85 nm from 346.17 nm? The grating has a length of 5.0 cm in length and there are 5500 grooves per cm.Assume first-order diffraction.

A____________________ disperses light into its component wavelengths and selects a narrow band of wavelengths to pass on to the sample or detector.

Which of the following monochromator terms is NOT correctly defined?

Which is NOT an appropriate detector for a spectrophotometer?

____________________ are optical sensors based on an optical fiber.

Which is NOT true for photodiode arrays?

The signal-to-noise ratio for a single spectrum is 2.18.How many additional scans are required to increase the signal-to-noise ratio by a factor of 50?

Two components of an interferometer are a moveable mirror and a beam splitter.Which of the following are NOT true statements regarding each component in creating an interferogram? I When the mirror travels a distance of /4,deconstructive interference occurs. II The beam splitter alternates the incident light between a reference and the sample. III When the mirror travels a distance of /2,deconstructive interference occurs. IV The beam splitter splits the incident light between the stationary mirror and the moveable mirror.

Which of the following statements regarding double beam spectrophotometers is NOT true?