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## Homework Statement

Hi

It is I again! Can someone please tell me where I went wrong? My answer is all over the place!

A narrow beam of light is directed normally at a single slit. The diffracted light forms a pattern on a white screen. A blue filter is placed in the path of the beam before it reaches the slit. The distance across five fringes including the central fringe is 18mm. Calculate the width of the central fringe

## Homework Equations

Using W= (2 x wavelength x D)/a

## The Attempt at a Solution

Solution:

Wavelength = 475nm (450-495 range)

D = 18mm

a= 5 (?)

I got 3.32nm!

Anybody???