The diffracted light from a periodic line grating is observed with a goniometer. The diffraction angles of spectral lines in different orders of diffraction are measured for the spectral lines from a Hg spectral lamp. By using gratings with different grating constants the angular spectral dispersion in dependence on grating constant is determined.
The effect of the total number of grating lines taking part in the diffraction is observed by reducing the beam width with an adjustable slit and the diffraction on that slit is taken into account. The spectral resolving power of a grating with given grating constant and useful beam width is observed and compared with theoretical considerations.
Benefits
understand fundamentals of spectroscopy
compact setup
precise and reproducible results
Tasks
Adjustment of the grating spectroscope
Measure the diffraction angle for different wavelenght and order of diffraction
Measure the diffraction angle for different grating constants
Identify the mercury (Hg) spectral lines
Determine the grating constant for known spectral lines
Determine the angular dispersion in dependence on grating constant
Observe the spectral resolving power with reduced beam width - when can spectral lines still be separated?
What you can learn about
Maxwell relationship
Dispersion
Polarisability
Refractive index
Prism
Rowland grating, Diffraction grating
Spectrometer
Goniometer
Constructive and destructive interference
Interference and diffraction on edge, slit, and grating