Question

a) What happens to the center spot as you slowly rotate the replica diffraction grating about its geometrical center? (Rotate here means to make the plane of the grating no longer perpendicular to the laser beam.)

b) What happens to the spots for n =1 and the spots for n = 2 as the grating is rotated?

c) Will you be able to observe the bright spots for n =1 and n = 2 if you spin the grating 90 ̊ while keeping the plane of the grating perpendicular to the laser beam? (In other words what once was the side of the grating, make it the bottom.)

Answer 1

Answer of a:

When the replica diffraction grating is rotated about its geometrical centre, the centre spot is also rotated in the same direction with same angle with respect to normal. When the replica diffraction grating is rotated clockwise at degree with respect to normal, the centre spot is also rotated toward clockwise at degree. When the replica diffraction grating is rotated counter clockwise at degree with respect to normal, the centre spot is also rotated toward counter clockwise at degree.

Answer of b:

As the replica diffraction grating is rotated clockwise or anticlockwise, the centre spot is also rotated at the same angle with respect to normal. For this reason, the n =1 and n = 2 spots are also rotated because they are diffracted rays and make diffraction angle with the normal.

Answer of c:

When spin is rotated , the incidence light is completely blocked by the grating and no n =1 or n = 2 spots are observed.