Measurement and comparison of refractive index of the water samples collected from different surface water sources in Namibia

A thesis submitted in partial fulfilment of the requirements for the Degree of Master of Science

Refractive index is an important optical parameter that exhibits the optical properties of materials. Single-Diffraction Method (SDM) and Abbe’s Refractometer Method (ARM) have been used for the measurements of refractive indices of twelve water samples collected from different surface water sources in Namibia. SDM employs a diffraction grating, rectangular glass cell and Ne-He laser emitting a monochromatic light of 632.5 nm. Refractive indices of water samples were measured without knowledge of refractive indices of the diffraction grating and the rectangular glass cell, and without measuring the angles of refraction, reflection and diffraction of the laser light. Experimental values obtained for refractive indices of the twelve water samples are presented. By comparison of refractive index values from SDM and ARM, their refractive index uncertainties values were lower than 0.1. This uncertainty error could be attributed to SDM instrument limitation error. More-over, turbidity, salinity, hydrogen ions (pH) and density values were measured for the water samples. From the statistical model, there exist non linear regression between salinity, pH and turbidity and the results from refractive indices from both methods. However, a linear correlation between SDM and ARM refractive index values was found to exist. Moreover, the correlation seems to exist between refractive index and density of water samples which is more notable in sea water samples. The root test was found to be 0.9535~1 for refractive index measurements from SDM and ARM.