The spacing between the slits of a diffraction grating is 1600 nm (1 nm = 10-9 m). how many lines per mm does this grating have?

Explanation:

It is given that,

Slit spacing,

We need to find the lines per mm in the grating. The relation between the slit spacing and number of lines is given by :

N = 625000 m

or

So, number of lines per mm is 625. Hence, this is the required solution.