- #1
Kalibasa
- 21
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Homework Statement
I'm really struggling with this one.
"A diffraction grating with 600 lines/mm is illuminated with light of wavelength 500 nm. A very wide viewing screen is 2.0 m behind the grating."
a) What is the distance between the two m=1 fringes?
b) How many bright fringes can be seen on the screen?
Homework Equations
d sinθ= mλ where d is the distance between the slits in the grating and m is the diffraction order of the fringes
y=Ltanθ where y is the distance between the fringes and L is the distance to the viewing screen
The Attempt at a Solution
I finally got the first part. I found d (d=1/N where is slits/mm) and then using d sinθ= mλ, I solved for θ for both fringes and then plugged this into y=L tanθ. I found the difference between these two y values (0.629 m each way) to get 1.3 m, which the book says is correct.
But now I have no idea how to solve the second part. How can I know how many fringes there are on the screen if I don't know the width of the screen?