How Do You Calculate the Density of a Diffraction Grating?

[kinst]

Homework Statement

A diffraction grating uses light with a wavelength of 475 nm to generate an interference pattern. if the highest order maximum that appears is the fifth-order. what is the density of the grating in lines/cm?

Homework Equations

sinθ = mλ / d
t= (m + 1/2) (λ) / 2

The Attempt at a Solution

t = (m + 1/2) (λ) / 2
t - (5 + 1/2) (475 x 10^-9) / 2
t= (2.6125 x 10^-6) / 2
t= 1.30625 x 10^-6 cm


so i got the answer in cm and t is for thickness, but the question wants the answer in lines/cm, and i don't know how to get it like that, so please anyone can help

 

[kinst]

can anyone help??

 

[FreeZin]

maybe u can use 1/2t