a) A 900 line/mm diffraction grating is illuminated by light of wavelength 600 n

Question

a) A 900 line/mm diffraction grating is illuminated by light of wavelength 600 nm. How many bright fringes are seen on a paper 0.20-m-wide screen located 0.5 m behind the grating? ( Hint: assume fringe , m=0 is at the center of the paper; hence, you have 10 cm available in each side of the center fringe to determine the number of fringes you will get in total.)
b) What is d the separation of the slit in nm?
c) What is the angle form between the first fringe ( Ym=1) and the central fringe (Ym=0 ).
(Hint: To solve this you must first find the Height of Ym =1 )

Explanation / Answer

(b) 900 lines / mm = 9.0^5 line/m ..
slit separation = 1/ 9.0^5 = 1.111^-6m .. .. , d = 1,111^-9m (nm)

(a) The max angular displacement across the half-screen width ..
Tan = 0.10m / 0.50m = 0.20 .. .. = 11.30º(max)
From the grating equation .. sin11.30 = m/d
m(max) = d sin11.30 / .. .. 1.11^-6m x sin11.3 / 600^-9m .. .. m(max) = 0.36 !!

not even m = 1 falls on the screen

i,think there is some thing wrong in the data!

thanks

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