Fringe Separation with a sheet of Glass

[BreadTomato]

Homework Statement

State a change to the separation of the fringe when a sheet of glass is placed in front of the bottom slit (this is a Double Slit Experiment). The light being passed is monochromatic red light.

Homework Equations

x = (landa)D / a

The Attempt at a Solution

After looking through the solution given to me, it appears that there will be no change to slit separation except that the fringe pattern shifts down, however I am unsure as to why no refraction occurs considering that light can refract, and wouldn't that change the fringe pattern depending on how the light diffracts out of the block?

Thank you very much!

 

[Khashishi]

The given solution looks fine.
Why do you say this: "I am unsure as to why no refraction occurs considering that light can refract"?
Does the solution say that no refraction occurs?

 

[rude man]

The sheet of glass is assumed planar so no refraction occurs, just a change in phase between the two slit sources going to the screen.