How many lines in a grating must be illuminated to obtain a resolving power of 300 in a third-order spectrum?
A)900
B)100
C)300
D)10

Question

Quizplus · Accepted Answer

Resolving power, R= Nm where N is the number of lines illuminated and m is the diffraction order. Given m=3 and R=300. Therefore, N= R/m = 300/3 = 100. So, 100 lines in a grating must be illuminated to obtain a resolving power of 300 in a third-order spectrum. Hence, the correct answer is option B).

How Many Lines in a Grating Must Be Illuminated to Obtain