#### kreil

Gold Member

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**1. The problem statements, all variables and given/known data**

1) A think flake of mica (n=1.58) is used to cover one slit of a double-slit arrangement. The central point on the screen is now occupied by what had been the seventh bright side fringe (m=7) before the mica was used. If the wavelength=550nm, what is the thickness of the mica?

2)The reflection of perpendicularly incident white light by a soap film in air has an interference maximum at 600nm and a minimum at 450nm, with no min inbetween. If n=1.33 for the film, what is the film thickness, assumed uniform?

**2. Relevant equations**

[tex]2nt=m \lambda[/tex] (for destructive interference)

[tex]2nt=(m+ \frac{1}{2}) \lambda[/tex] (for constructive interference)

[tex] d sin(\theta)=m \lambda[/tex] (condition for bright fringes)

[tex] d sin(\theta)= (m+ \frac{1}{2}) \lambda[/tex] (condition for dark fringes)

**3. The attempt at a solution**

1) What confuses me here is that the mica only covers one slit. How is this taken into account? Can I just use the equations above?

2) Very lost on this one. Do I use the fringe equations to solve for m, which can then be used in another equation to solve for thickness.

Any other info on these questions is more than welcome.

Thanks,

Josh