To make the central fringe at the center O. A mica sheet of refractive index 1.5 is introduced. Choose the correct statements(s)

To make path difference 0 at O.Mica sheet has to be introduce in front of  S1Geometrical path difference before entering slits should be balanced by optical path difference due to mica sheet.Before entering slits ∆xGeom=SS2-SS1=2d-d=2-1dAfter passing through slits ∆xoptical=S1O-S2O=μ-1t(2−1)d=(μ−1)t⇒t=(2−1)d(μ−1)⇒t=2(2−1)d