Simple prism coupling technique to measure the refractive index of a liquid and its variation with temperature

We present a simple and novel prism coupling technique for the measurement of the refractive index of a liquid and its variation with temperature, which is typically ∼10−4/°C. The proposed experimental setup is based on a simplified version of the conventional critical angle method, and uses components easily available in an undergraduate laboratory. Experimental details and results of the measurements carried out on water and ethyl alcohol are reported, along with a discussion on the various sources of error. The measured values of the refractive indices and their temperature dependence are in good agreement with the standard values. Errors in the measured values of refractive index and its variation with temperature are less than 0.1% and 10%, respectively. The most attractive feature of the proposed technique is the simplicity of the experimental set up, which consists only of a prism and a light source (preferably a laser source).