if light of wavelength 6000 Å is made to incident over a thin film of refractive index 1.5 then minimum thickness of film for constructive interence in reflected light is :

Options

A. 1000 Å
B. 2000Å
C. 3000Å
D. 6000Å

Answer

A

Explanation

For constructive interference in reflected light
`2mu t cos r =(2n -1 )(lamda)/(2) `
` t=((2n-1)lamda)/(4 mu cos r)`
` t= ((2n-1)xx6000Å)/(4xx1.5xx1)`
`t=(2n-1)xx1000Å`
n=1
`t_("min")= 1000Å`