Biology Cabinet

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Optical Path Lenght of Low Density Polyethylene Film
By Nasif S. Nahle
July 23, 2011

The following graph depicts the Optical Path Length (OPL) of a sheeting of Low Density Polyethylene at different wavelengths in the optical spectrum. The light reflected by the inner surfaces of the boxes used in the Greenhouse Effect Experiment is not monochromatic; consequently, the principle of Coherence doesn't apply.

Additionally, the Extinction Coefficient of Polyethylene Film is 0.0, which means that the solar radiation does not suffer any change after crossing the film. The radiation emitted by the inner surfaces of the boxes either change after they cross the sheeting of polyethylene film.
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The phase shift of the sunlight waves is 0.00834 nm; therefore, the coherence principle does not apply in the case of sunlight passing through a polyethylene film because the sunlight is not monochromatic and its phase change is negligible.

On the other hand, the light reflected by the inner surfaces of the box covered with polyethylene film is either monochromatic; consequently, the principle of coherence cannot be applied on the radiation emitted by those surfaces. The phase change of the light reflected by the inner surfaces is 0.001 nm, consequently the coherence principle either applies in this case because the phase change of the reflected radiation (0.1) is negligible (0.001).

The thickness of one of the sheets of polyethylene film that I used in my experiment was 0.051 mm. This number must be taken into account to calculate the Optical Path Length (OPL) and the phase shift of the waves of sunlight and of the light reflected by the surface The cover of 0.051 mm thick polyethylene film was replaced with a cover of 0.3 mm thick polyethylene film.

The results did not vary considerably, as the following graph shows: