The Diffraction Grating for A Level Physics

 

Diffraction grating is a glass slide with a series of parallel transparent

lines, called slits, on it.

When a beam of monochromatic beam strikes it, light waves diffract through the slits, creating a pattern of alternating bright and dark spots, known as fringes, on a surface where light falls - in addition to a central, wider bright spot.

At the centre, the light waves meet up in phase. On either side of the central fringe, however, they meet up with with increasing path differences between the waves in question.

 

 

For bright fringes, the path differences are multiples of λ and for the dark fringes that alternate between the bright fringes, the path differences are multiples of λ/2.