posted by jay .
White light strikes a grating with 1300 lines/cm at normal incidence. How many complete visible spectra will be formed on either side of the central maximum? (Take the range of visible wavelengths to be 400 - 700 nm.)
I used the equation
d sintheta = m wavelength: (1/1300cm)(1000)= [0.769m x sin90]/400nm = 1 (since you are supposed to round down). I tried with 700nm and 700-400=300nm. So, my answers were 0,1,2, or 3; all are wrong! Any help?