Distance between m=0/m=1 bright fringes

[crazyog]

Homework Statement

Two slits separated by 2.00x10^-5 are illuminated by light of wavelength 500nm. If the scree is 8.0m from the slits what is the distance between m = 0 and m=1 bright fringes?
answer is 10 cm

Homework Equations

d=m*lambda*L/y (for the short cute..for small angles)

The Attempt at a Solution

at m=0 d=0

at m=1
d=1*(500*10^-9)(8.0 m)/(2.0*10^-5) = 0.2m

so I am getting double...but I can't find a reason t multiply it by 1/2 ...

hmm
please help!

also, do i alway use m for bright fringe and (m+1/2) for dark...?

 

[crazyog]

I figured out there was a mistake on the answer sheet and the answer is 20 cm


haha thanks anyways