How Does the Central Maximum Shift When a Laser Beam's Angle Changes?

[physics2011]

Homework Statement

A laser beam, with a wavelength of 532 nm, is directed exactly perpendicular to a screen having tow narrow slits spaced .15 mm apart. Interference fringes, including a central maximum, are observed on a screen 1.0 m away. The direction of the beam is then slowly rotated around an axis parallel to the slits to an angle of 1.0 degrees. By what distance does the central maximum on the screen move?

Homework Equations

Theta=m(lambda/d)
ym=(m*L*lambda)/d

The Attempt at a Solution

I do not understand how to find the position change of the central maximum because for the central maximum, m=0 so the position goes to 0 regardless of the angle of incidence of the light. Basically, I can't figure out how to even set up the problem.

Thanks

 

[aim1732]

When light is incident at an angle on the set-up there is some path difference between the initial rays starting from the slits so that the central maximum - the point where path difference is zero - shifts. You can try finding out this path differnce by construction.