Slit Diffraction in Water: Solving for the Distance Between Dark Fringes

[sghaussi]

slit diffraction in water?

Hello! I'm having trouble answer this homework problem:

Suppose the entire apparatus (light of wavelength X nm from a distant source is incident on a slit Y mm wide, and the resulting diffraction pattern is observed on a screen Z m away) is immersed in water (n=1.33).

Then what is the distance between the two dark fringes on either side of the central bright fringe?

I know what I want to use the equation for Dark fringes in single-slit diffraction:
sin(theta) = m*lamda/a

in my case, m = 1
and a = y

I'm not sure how to solve this problem now that the entire apparatus is immersed in water? I know water affects this, but how? Can you help me start this problem?

 

[Doc Al]

How does the wavelength of light depend on the index of refraction of the medium?

 

[sghaussi]

thanks! i knew it was a concept I had studied a few chaptes earlier but it completely slipped my mind. that's right, index of refraction depends on c and hte speed of light in that particular medium! =)