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Dispersion and resolving power of  a grating spectroscope

Dispersion and resolving power of a grating spectroscope

Item no.: P2210300

Experiment Type: Teacher Experiment, Laboratory Experiment

Difficulty Expenditure of Time print
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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. 


  • understand fundamentals of spectroscopy
  • compact setup
  • precise and reproducible results



1. To adjust the spectrometer-goniometer.

2. To determine the refractive index of various liquids in a hollow prism.

3. To determine the refractive index of various glass prism.

4. To determine the wavelengths of the mercury spectral lines.

5. To demonstrate the relationship between refractive index and wavelength (dispersion curve).

6. To calculate the resolving power of the glass prisms from the slope of the dispersion curves.

7. Determination of the grating constant of a Rowland gratin based on the diffraction angle (up to the third oder) of the high intensity spectral lines of mercury.

8. Determination of the angular dispersion of a grating.

9. Determination of the resolving power required to separate the different Hg-Lines. Comparison with theory


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 
  • Spectral resolving power
Document     Filesize
p2210300e.pdf Experiment guide, English 528.43 KB

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