A diffraction grating is illuminated with yellow light. The diffraction pattern seen on a viewing screen consists of three yellow bright fringes, one at the central maximum and one on either side of it at . Then the grating is simultaneously illuminated with red light. Where a red and a yellow fringe overlap, an orange fringe is produced. The new pattern consists of .

(d) an orange fringe at 0°, yellow fringes at ±50°, and red fringes farther out

Explanation:

The available multiple choice to the question is:

(a) only red fringes at 0° and ±50°

(b) only yellow fringes at 0°and ±50°

(c) only orange fringes at 0∘ and ±50°

(d) an orange fringe at 0°, yellow fringes at ±50° , and red fringes farther out,

(e) an orange fringe at 0°, yellow fringes at ±50°, and red fringes closer in.

Further Explanation:

In diffraction there is a spot at 0° for all wavelengths, so the red fringe and yellow fringe will combine there to make orange fringe. However, the angle of diffraction increase with an increase in wavelength. The red fringer has a longer wavelength than the yellow fringe, so the yellow fringe will be at ±50°, and the red fringe farthers out.