Question

light of wavelength 400 nm shines through a diffracting rating making fringes on a screen 60 cm from the grating. a first order bright fringe is obersved on that screen 30 cm from the central maximum. how far from the central max would a first order bright fringe fall on that screen from light of wavelength of 800 nm?

Answer 1

y = L tan

so,

tan = y / L

= arctan ( y/L)

where y is distance between center maximum and first order fringe

so,

= arctan (0.3 / 0.6)

= 26.56 degree

so,

separation between slits,

d = m / sin 26.56

d = 1 * 400e-9 / sin 26.56

d = 894.42 nm

Now,

for = 800 nm

sin = 1 * 800 / 894.42

= 63.43 degree

so,

y = L tan

y = 60 * tan 63.43

y = 120 cm