physics
posted by Rach .
A diffraction grating gives a secondorder maximum at as angle of 31‹ for violet light (ƒÉ = 4.0 ~ 102 nm). If the diffraction grating is 1.0 cm in width, how many lines are on this diffraction grating?

Sorry about the double post, and
the question is:
A diffraction grating gives a secondorder maximum at as angle of 31 degrees for violet light (wavelength = 4.0 x 102 nm). If the diffraction grating is 1.0 cm in width, how many lines are on this diffraction grating? 
n lambda = d sin( theta )
d=n * lambda/sinTheta
solve for d. That is the distance between slits, so lines/distance= 1/d
change wavelength to cm if you want lines per cm 
isn't that derived from the formula used for single slit though? and this is multiple slit (isn't that the same eqns as double slit?

so n= 2 (second order)
theta= 31 degrees
d= 0.1 m
lambda= 4.0 x 10^7 m
(i'm required to solve in m)
is this correct? 
no