# Far-field interference pattern in double slit experiment

## Homework Statement

An interference experiment employs two narrow parallel slits of separation
0.25mm, and monochromatic light of wavelength $$\lambda$$ = 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.
$$\lambda$$ = 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/$$\lambda$$<<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.

## Answers and Replies

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