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## Homework Statement

An interference experiment employs two narrow parallel slits of separation

0.25mm, and monochromatic light of wavelength [tex]\lambda[/tex] = 500 nm. Estimate

the minimum distance that the projection screen must be placed behind

the slits in order to obtain a far-field interference pattern.

[tex]\lambda[/tex] = 500nm

d = .25mm = 2.5 *10^5 nm

D = distance to projection screen

## Homework Equations

I know that for a far-field interference pattern to emerge, d/D<<1 and d^2/[tex]\lambda[/tex]<<D

## The Attempt at a Solution

I don't know how to get an exact value for a minimum value of D. I know that D must be much greater than 125mm from the above, but I don't know how to get anything more specific than that.