Question

What value would u give the actual index of refraction of the plastic block?

Answer 1

About `n=1.5`.

Explanation:

You can check the a list to find out what indexes of refraction for plastics are. It is hard to find out these values theoretically and are often found experimentally.

Different plastics have different indexes of refraction. Also, each plastic has slightly different indexes at different wavelengths of light, though this difference is usually small. For example, the plastic acrylic has an index around `n = 1.498` where as Polystyrene (a different plastic), has an index around `n = 1.604`. These values are true of light with a wavelength of `486.1`nm which is the color blue. For acrylic with red light (wavelength `= 656.3`nm), `n` only equals `1.489`.

This causes color dispersion or rainbows when light diffracts enough to separate different wavelengths of different colors.

(Other factors also vary the index of refraction, such as temperature. The numbers above assume a temperature of `20` degrees Celsius).

Thus, the index of a block of plastic varies depending on the type of plastic, the wavelength, and even the temperature. But common values hover around `n=1.5`. Of course, the best way is test the block of plastic.