Preparation

Experiment: Finding the refractive index of a substance

Aim: Estimate the refractive index of perspex and vegetable oil.

L1 |LR |sin i |sin r |R.I | |90 |90 |1|1 |1 | |80 |42 |0.98 |0.67 |1.47 | |70 |39 |0.94 |0.63 |1.49 | |60 |35 |0.87 |0.57 |1.51 | |50 |32 |0.77 |0.53 |1.44 | |40 |25 |0.64 |0.42 |1.52 | |30 |21 |0.50|0.36 |1.39 * | |20 |13 |0.34 |0.22 |1.52 | |10 |7 |0.17 |0.12 |1.42 | |
The data collected relates to the aim, as the angle of incidence and the angle of refraction,are obtained and were able to be used, to find the relationship between both sets of results.

Uncertainty
The protractor used in this experiment was accurate to1.0° the Reading Uncertainty is half of this value – ±0.5° .

Mean refractive index = 1+1.47+1.49+1.51+1.44+1.52+1.39+1.52+1.42 = 1.42
9

ApparatusSemicircular perspex
Light box
Protractor
Generator

Method
1) Place the semicircular perspex block within the contours of the
semicircle drawn on the grid provided.2) Shine a single ray from the ray box along the 10 degrees line and
mark the position of the refracted ray with a cross.
3) Do likewise for the rest of the lineswith the assigned degree
value.
4) Remove the perspex block and draw lines to mark each refracted ray.
5) Measure the angles of refraction with the protractor andrecord
them onto the Results Table provided.
6) Do so for the rest of the Results Table.

Graph to verify the snell’s law

Conclusion
The refractive index ofPerspex, acquired through calculation, is 1.42. Neither method is totally accurate, but the value from the graph is close to the correct refractive index of Perspex.