Question

. Light travels at different speeds through materials due the refractive index of that material. Given that I have a transparent polymer material, would light travel faster or slower through it if it (a) have zero stress on it or (b) have a substantial, but still elastic, stress on it (say 20 MPa for HDPE)? Explain.

Answer 1

Hey there!

Given the conditions , we know that the refractive index can be given with the formula, n = c/v , where c is the velocity of light in vacuum and v is the velocity of light in that medium. The ratio between these two ratios are given as refractive index. In that case , as the opaqueness of the material increases, the refractive index increases along, in that case the refractive index through a transparent material can be assumed to be among the 1.5 - 1.8 range.

(a) If there is no stress, then it means that the material is in a normal condition. So we could say that the refractive index is going to be the same. Hence there would be that slight decrease in the speed when it passes through the material in accordance with it's refractive index as always. No additional increase or decrease in speed of light in the material.

(b) Let me say that , density increases with increased stress experienced on the material. Hence materials with increased density have higher refractive index. In that case, higher refractive index means that the material reduces the speed of light through the material.

I hope the explanation helps... Cheers :)