Lets say if a double slit were to be put into water. I understand that water has a bigger index of refraction than air so thus if you put a double slit into water you will get a smaller wavelength; because as the index of refraction increases wavelength decrease. Using the double slit formula; m (wavelength)= d sin Theta. You see that wavelength gets smaller the angle gets smaller making the the bright fringe closer together. Im not understand where in the formula shows bright fringe getting closer, cause i thought the D represents the length of the slit. And if thetha gets smaller does the "D" get bigger? how do i know that the bright fringe is getting closer together based on the formula?