question_answer

When light of wavelength \[\lambda \] falls on a thin film of thick- ness t and refractive index n, the essential conditions for the production of constructive interference fringes by the rays A and B is: (m = 1,2,3,...)

A)  \[2nt\,\cos \,r=\left( m-\frac{1}{2} \right)\lambda \]

B) \[2nt\,\cos \,r=m\lambda \]

C)  \[nt\,\cos \,r=\left( m-\frac{1}{2} \right)\lambda \]

D)    \[nt\,\cos \,r=m\lambda \]