13) Light with a wavelength of 550 nanometers in air travels with a speed of 1.9

Question

13) Light with a wavelength of 550 nanometers in air travels with a speed of 1.96 x 10^8 meters/second in a certain liquid. Calculate the index of refraction.
>answer is 1.53, why??

19) Consider unpolarized light, intensity I0, that enters a system of two polarizing sheets. The direction of motion for the light is along the positive z axis. After passing thru the first sheet, the intensity is I1 and the light is polarized parallel to the y axis. The light then passes through a second sheet with its polarizing axis forming a 30 degree angle with the first sheet. The intensity, I2, after the light passes through the second sheet is

the answer is I0 (cos^2 30o)/2, why??

Explanation / Answer

a) Given that

              v = 1.96 x 108 m/s

              = 550 nm

    We know that

             Refractive index = c / v

                                         = 3 x 108 / 1.96 x 108

                                         = 1.530

(b)

According to Malus law, we have

           I = Io cos2

When light passes through first sheet the intensity of the light is = Io / 2

With this intensity the light passes through second sheet so that

          I = I0 (cos2 30o)/2

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