A grating spectrometer is used to resolve wavelengths 660.0 nm and 661.4 nm in second order.
(a) How many slits per centimeter must the grating have to produce both wavelengths in second order? (The answer is either a maximum or a minimum number of slits per centimeter.)
(b) The minimum number of slits required to resolve two closely spaced lines is N = λ/(m Δλ), where l is the average of the two wavelengths, Δλ is the difference between the two wavelengths, and m is the order. What minimum number of slits must this grating have to resolve the lines in second order?