Question

(b)Monochromatic light from a helium-neon laser of λ = 632.8 nm is incident on a diffraction grating containing 6000 lines/cm.(i)Analyse the number of bright fringes that can be observed.(2 marks)(ii)Calculate the angle for each bright fringe that occur.

Answer 1

The distance between two lits will be = lon bocorre d = 1cm = 0.1666X163x10 m = 0.1666x105m =1.66X 10 am Gooolnes So; d = 1.66*10-6m. → Now, to calcuble the no. of visible fringe: - for visibility of bright fringe in one half of screen o=90°. Thus, ma=dsino and=dsingoo Coin 96-1) n= order of maxima A = wavelength of sance used de distance blw slit, angle of diffection nad na=d =d This will give arden of maxima detained on one half of screen. So, total bright fringes = central maxmat bright fringe on both half of screen toted bright fringes= ant 1 1-66810 bin -0.00263x16 633.8% 10m This, m= 9.63

1x 63218X10 In The value of h can only be integer So, we will see bright fringes upto order of n=2, Total no. of bright foringes visible = ant! =2(2) H=5 Total no. bright fringes of risike E5 (i) To calculate angle for each bright fringe to occure- Put n=1,2 referately. > for na 1 :- na= dsino y 1.66x10 mx GX Sino sino = 381.20488 10 3 Sino = 0.3812048 , Orsino. (0-3812048) O= 29.40 for ne!- nd=dsino, 3 9x632-8x10mm = 1.66X10-m x sino Sino = 0,762409, 0= sint(0762409) o = 49.679,