Interference and polarization problems with wavelength 6000 Å

[Hrithik]

1.in an intrfrnce expmnt. wit monochromatic light of wavlngth 6000 AU only 50 fringes are observable.estimate d coherence of d source.

2.show a circularly polarised lght is eqvlnt to 2 mutually perpendicular plane polarised lt wit a phase diff of pie/2.

3.fringes of equal inclination are formed with a 2mm thck plnpll glass plate of n=1.50.how many fringes are formed entirely ? w=6000 AU

 

[Hrithik]

any help on what eqs to use please