193 - Interference at the gitter

193 – Interference at the gitter

Color spectrum due to interference  

 

Introduction to:  

  • Interference  
  • Light spectrum  
  • Spectral analysis  

 

Material:  

  • CD (Compact Disc)  
  • Flashlight  
  • Shade to catch the light (e.g. white wall)  

Instructions: 

  • Light at an angle of about 45° on the CD  
  • Hold the CD so that the reflected light falls on the screen  

Observation:  

  • In addition to a very bright, white luminous dot, you can see a colorful color spectrum.   
  • In addition, there may be a second spectrum that is much weaker.  

Explication: 

  • The grooves of the CD act as a gitter through which the light rays of the flashlight pass.  
  • The bright point of light is the main maximum of the interference figure, the colorful spectrum results from the first minor maxima. Depending on the frequency of the light, the first secondary maximum is at a different location.  
  • It is possible that the spectrum of the second minor maxima can still be seen.  

Tips:  

  • The gitter spacing of the grooves of the CD is 1.6 μm. This information can also be used to carry out quantitative measurements or calculations.