DIFFRACTION GRATING - Q10

10) Distinguish between a grating spectrum and a prismatic

spectrum.

Ans: Grating spectrum is a spectrum produced as a result of diffraction by a grating whereas; prismatic spectrum is a consequence of dispersion of light by a prism.

• In grating spectrum we can observe different orders of spectral lines on either side of spectrum which do not happen in prismatic spectrum.
• The prism spectrum is brighter than grating spectra.
• In case of a prism, the deviation is least for red and greatest for violet. While, in case of grating, deviation is least for violet and greatest for red. Hence, in prism spectrum, spectral colors are in order from red to violet. But in grating spectrum, spectral colors are in order from violet to red.
• Prism spectrum depends on nature of material of prism but grating spectra do not depend on material of grating.
• Resolving power of grating spectra is large. And that of prismatic spectrum is small.