Question

a physics teacher has demonstrated a single slit diffraction experiment to the students with a light source of wavelength 400nm and grating constant of 4000 lines per inch. Compute maximum number of dark fringes observed by him? If he replaces the given grating with another grating (5000 lines per inch) will he observe the same number of dark fringes?

Answer 1

The number of minima in the first case is

$$n_1=\dfrac {d_1}\lambda-1=1.$$

For another grating, it is

$$n_2=\dfrac {d_2}\lambda-1=0.$$