Type-B optical flat is tested for parallelism. What is the formula for the difference of the thickness of the flat at 2 points on the adjacent fringe? ( is the refractive index)

Type-B optical flat is tested for parallelism. What is the formula for

1.	Type-B optical flat is tested for parallelism. What is the formula for the difference of the thickness of the flat at 2 points on the adjacent fringe? ( is the refractive index)
A.	/2*(1/ ) microns
B.	/4*( ) microns
C.	* microns
D.	*( /2) microns
Answer» B. /4*( ) microns