JEE Main & Advanced Physics Wave Optics / तरंग प्रकाशिकी Diffraction Gratings

One of the most useful tools in the study of light and of objects that emit and absorbs light is the diffraction grating.

(1) this device consists parallel slits of equal width and equal spacing called rulings, perhaps as many as several thousand per mm.

(2) The separation (d) between rulings is called grating spacing. (If N-rulings occupy a total width \[\omega \], then \[d=\frac{\omega }{N}\])

(3) For light ray emerging from each slit at an angle \[\theta ,\] there is a path difference \[d\sin \theta ,\] between each ray the one directly above. The d is called the grating element

\[d=a+e\]

where a = width of the slit e = opaque part

(4) The condition for formation of bright fringe is \[d\sin \theta =n\lambda ,\]where n = 0, 1, 2, .... is called the order of diffraction.