Question

An observer looks down on two glass plates, one placed on top of the other. The top plate pivots about a line of contact at its edge as shown in the figure. The angle created by the pivoting motion increases in time. Which is true?

1. The entire plate surface alternates between dark and bright as time advances    
2. The width of alternating bright and dark fringes aligned parallel to the line of contact increases with time.    
3. The width of alternating bright and dark fringes aligned parallel to the line of contact decreases with time.    
4. The width of alternating bright and dark fringes aligned perpendicular to the line of contact of constant in time, but become blurrier as time advances.