A Film of Index of Refraction N₁ Coats a Surface $\lambda$

Multiple Choice

A film of index of refraction n₁ coats a surface with index of refraction n₂.When n₁ < n₂,the condition for constructive interference for reflected monochromatic light of wavelength $\lambda$ in air is

A) $t = m \frac { \lambda } { n _ { 1 } }$ .
B) $t = \left( m + \frac { 1 } { 2 } \right) \frac { \lambda } { n _ { 1 } }$ .
C) $2 t = m \frac { \lambda } { n _ { 1 } }$ .
D) $2 t = \left( m + \frac { 1 } { 2 } \right) \frac { \lambda } { n _ { 1 } }$ .
E) $4 t = m \frac { \lambda } { n _ { 1 } }$ .