- #1
spaghed87
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Homework Statement
A 550 lines/mm diffraction grating is illuminated by light of wavelength 550nm.
How many bright fringes are seen on a 3.1-m-wide screen located 2.1m behind the grating?
Homework Equations
[tex]\Delta[/tex]Y = [tex]\lambda[/tex]*L/d
where Y is equal to the fringe spacing... lamda is equal to the wavelength. d is equal to the separation... which is 0.001m/550lines in this case.
The Attempt at a Solution
I did [tex]\Delta[/tex]Y=(550*10^-9m*2.1m)/(~1.81*10-6) = 0.63525m
So then the width of 3.1m divided by the fringe spacing ~1.81*10^-6 gives me 4.87 which is unitless because it is n and equal to the number of gaps... now there are two fringes per gap so shouldn't the answer be 6? well... the last one is cut off so i can't round... so that would be 5 right? but mastering physics (my online homework website) still says I'm wrong. any ideas?