Posted by physics on .
Monochromatic light from a heliumneon laser (wavelength=632.8 nm) shines at a right angle onto the surface of a diffraction grating that contains 130 960 lines/m. Find the angle at which one would observe the firstorder maximum.
formula: (a+b)Sin theta = n wavelength
(a+b) = 1
____ m; n=1
wavelength=632.8*10^9 m
=6.328*10^7m
Sin theta=6.32^8 * 10^7 * 130960
= 6.328*10^7*130960*10^5
theta= 4.7536deg
= 4.75
is this done correctly?
130960

physics 
drwls,
I don't know what a and b are supposed to be in your diffrection grating formula. The correct form of the quation is
d (sin i + sinr) = m*lambda
where i and r are the angles of incidence and reflection.
In your case sin i = 0, m = 1, and d is the grating line separation, which is your case is 1/(130960m^1) = 7.636*10^6 m.
Therefore
d sin r = 632.8*10^9 m
sin r = 632.8*10^9*130960 = 0.08287
r = 4.75 degrees
So you got the right answer, anyway