Question

A red laser with wavelength 650 nanometres and a blue laser with wavelength 473 nanometres are red at
a difraction slit of width 0.1mm then onto a screen a long distance away.
A central bright point is formed at the same place for each laser. Calculate the ratio of the distances from
this central point to the next bright fringe for the two lasers (red / blue).

Answer 1

The condition for 1st diffraction minima is
  
where, d is the slit width. And lambda is the wavelength of the incident light. And for the large screen separation, we have the position of the first minimum from the central maxima is
   
And so,
   
  
And so, we have the position of the first maxima is
  
  
So, the ratio of the positions of the 1st bright spot in case for two different lights,