Semi-cilinder Optical Behavior

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Description of the Experiment

This experiment has multiple purposes:

  1. Determine the refraction index of Plexiglass and verify Snell's law;
  2. Measure the critical angle at which there is total internal reflection;
  3. Study the power transmited and reflected in an optical interface, proving conservation of energy;
  4. Study the power transmited and reflected as a function of laser polarization, determining Brewster's angle.

This analisis can be done qualitatively by processing the picture from the camera or quantitatively by using the light sensor that sweeps the semicilinder angle-wise. Because of experimental constraints, the avaliable angle range is only 0º through 240º.


Links

  • Video: rtsp://elabmc.ist.utl.pt/optica.sdp
  • Laboratory: Intermediate at e-lab.ist.eu[1]
  • Control room: optica
  • Level: ****

Experimental Protocol

Protocol I

The ray tracer mode allows a qualitative analysis of the transmission and reflection of light in the inerface between plexiglass and air through the pictures captured by the camera.

The user chooses the starting and ending angle for the sweep. With some pictures and Snell's law it is possible to calculate the refraction index for the denser material (plexiglass). We suggest using an image processing software like Corelpaint, Photoshop or Draw (openoffice.org) to analyse the pictures: simply find the light rays and measure the angle between them.

Note: selecting angles between 0º and 180º means the light will shine upon the curved side of the semi-cilinder, whereas between 180º and 360º the light will shine on the straight side.


Protocol II

Under construction.


Protocol III

Under construction.


Protocol IV

Under construction.