Question

With the use of diagrams, explain why the slit width of a prism wavelength selector must be varied to provide constant effective bandwidths (specific wavelengths) but a constant slit width instead can be used to provide constant bandwidth with a grating monochromator?

calculate the frequency in hertz, the wave number in cm-1 Calculate the frequency in hertz, the wave number in cm!, the energy in joules, and the energy associated with the 317 nm wavelength energy source achieved from a He-Ne laser and used in the detection of Quinine (a chiral compound used to treat malaria and babesiosis).

Answer 1

Wavelength selectors limit the radiation absorbed by a sample to a certain wavelength or a narrow band of wavelengths.  

The wavelength, that is the output keeps
changing continuously for a considerable
spectral range in case of a prism
Wavelength selector while in case of a grating
monochromator, the output wavelength
remains same, as the radiation is dispersed in
the component wavelength.
As the output wavelength keeps varying, the slit
width is also required to be varied in case of a
prism wavelength selector in order to keep the
effective wavelength constant which is not
needed in case of a grating monochromator.

Slit width must be varied to get constant
effective wavelength in case of prism
Wavelength selector while it is almost same in case
of grating monochromator.

Fig a: Prism wavelength selector

Fig b: Grating Monochromator

Numerical