# Single-slit Diffraction Question Pls help

1. May 31, 2009

### 9giddjl

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

Monochromatic light of 585 nm is shone on a slit of width 8.0 x 10^-2 mm and the interference pattern is produced on a screen 1.8 m from the source. What is the width of the first-order bright fringe?

2. Relevant equations

PD/w=x/L

3. The attempt at a solution
PD=? Im not sure what n would be.. thats my main problem
wavelength= 5.85 x 10^-7 m
L= 1.8 m
w= 8 x 10^-5 m

When I used n=1 wavelength, i got the right answer, but n=1 is the first order dark fringe.. can someone please explain to me this.. i would just like to know what n would be.. thankyou any help is muchly appreciated.

thankyou xie xie ni mm goi!

2. May 31, 2009

### Hootenanny

Staff Emeritus
Why do you think that?

Doesn't n refer to the nth maximum?

3. May 31, 2009

### mrblister68

single slit diffraction equations lead to dark fringes, however as the separation between two dark fringes and two bright fringes are the same, it does not make any difference