The “sodium doublet” in the spectrum of sodium is a pair of lines with wavelengths 589.0 and 589.6 nm. We have to calculate the minimum number of rulings in a grating needed to resolve this doublet in the second-order spectrum.
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Solution: Click For PDF Version The resolving power for a grating is given by the equation
where N is the number of rulings in the grating and m is the order of the grating spectra. For the “sodium doublet”
and
Therefore, in order that the “sodium doublet” are resolved in the second order of the grating spectra, the minimum number of rulings in the grating has to be
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