In: Physics
light from a discharge tube containing a particular gas illuminates a diffraction grating and is observed on a screen 75.0cm behind the grating. The emission at wavelength 621nm creates a first-order bright fringe 38.0 cm from the central maximum. What is the wavelength of the bright fringe that is 47.3cm from the central maximum?
For diffraction grating, we have
where is the diffraction angle for respective wavelength
let 1 be known wavelength of spectral line so that 1 = 621 nm and its diffraction angle 1 is tan-1 (38/75) = 27o
Diffraction angle 2 of unknown wavelength 2 is given as, 2 = tan-1(47.3/75) = 32o
Hence unknown wavelength 2 is calculated as,
2 = [ 1 / sin 1 ] sin2 = [ 621 / sin27 ] sin32 = 725 nm