Thinnest film in which the reflected light will be a maximum?

[vrobins1]

Homework Statement

Monochromatic light, at normal incidence, strikes a thin film in air. If (lambda) denotes the wavelength in the film, what is the thinnest film in which he reflected light will be a maximum?

Homework Equations

2d = (m+1/2)(lambda/n_film) for minimal reflection and

2d = m(lambda/n_film) for max reflection

The Attempt at a Solution

I used the second formula above:

2d = m(lambda/n) and solved for d;
I got d = lambda/2n , but someone else in my class says it is lamba/4n,

Can anyone offer any insight? Thanks!

 

[Carid]

I think this reference may be of some help.

https://www.physicsforums.com/archive/index.php/t-112763.html