A green laser pointer of wavelength 532 nm532\text{ nm}532 nm is incident normally on a diffraction grating. A student measures the angle between the central maximum and the second-order maximum to be 32.2∘32.2^\circ32.2∘.
What is the number of lines per millimetre of the diffraction grating?
250 lines/mm250\text{ lines/mm}250 lines/mm
500 lines/mm500\text{ lines/mm}500 lines/mm
800 lines/mm800\text{ lines/mm}800 lines/mm
1000 lines/mm1000\text{ lines/mm}1000 lines/mm
