Physics Interference & Diffraction
posted by Christina on .
Given Information: Light of wavelength 631 nm passes through a diffraction grating having 485 lines/mm.
Part A: What is the total number of bright spots (indicating complete constructive interference) that will occur on a large distant screen?
*Answer: 7 (this is correct)
Part B: What is the angle of the bright spot farthest from the center?
*Answer: ???
I am not sure what equation to use for this part of the problem....

There will be a bright spot wherever
d sin A = N *lambda,
where lambda is the wavelength, d is the line spacing, and N is an integer (including zero).
(1/485)*10^3 m sin A = N*631*10^9 m
sin A = N* 0.306
Allowed values of N are +/1,2,3 and 0
So there are seven bright spots
B. The center of the pattern is n=0. Compute the angle for which N = + or  3 and you will have the answer. 
Ooh wonderful! There is another problem similar to it...I am having trouble finding the # of fringes, but I think once I get help with that I can solve for the angle!!!
GIVEN: Light of wavelength 585 nm falls on a slit 6.66×10−2 mm wide.
Part A: On a very large distant screen, how many totally dark fringes (indicating complete cancellation) will there be, including both sides of the central bright spot?
*Answer: ?????
Part B: At what angle will the dark fringe that is most distant from the central bright fringe occur?
*Answer: I'm asuming that this will be the equation to use: d*sinA=(N+.5)*L