If the thickness of a plate is 0.0032 cm, what shall be the phase retardation for a light of wavelength 5000 Å, given the principal refractive indices are 1.55 and 1.54?

If the thickness of a plate is 0.0032 cm, what shall be the phase reta

1.	If the thickness of a plate is 0.0032 cm, what shall be the phase retardation for a light of wavelength 5000 Å, given the principal refractive indices are 1.55 and 1.54?
A.	1.05π radians
B.	1.15π radians
C.	1.25π radians
D.	1.35π radians
Answer» C.