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Imagine you have two identical perfect linear polarizers and a source of natural light. Place them one behind the other and position their transmission axes at 0 and 50 degrees respectively. Now insert between them a third linear polarizer with its transmission axis at 25 degrees. If 1000 W/cm2 of natural light is incident, how much will emerge with and without the middle polarizer in place?

Respuesta :

Answer:

Without the third polarizer inserted in the middle of the first and second polarizer the irradiance of light that would emerge from the second polarizer is

             [tex]I_2=321.39 W/cm^2[/tex]

With the insertion of the third polarizer  at the middle of the first and second polarizer the irradiance of light that would emerge from the second polarizer is

              [tex]I_4 = I(\theta_d_1) = 337.3 W/cm^2[/tex]

Explanation:

From the question we are told that the

         The angle between the transmission axis of first linear polarizer and the vertical axis  is [tex]\theta_1 = 0^o[/tex]

                   The angle between the transmission axis of second linear polarizer and the vertical axis  is [tex]\theta_2 = 50^o[/tex]  

                   The angle between the transmission axis of third linear polarizer and the vertical axis  is [tex]\theta_2 = 25^o[/tex]  

         The  irradiance of the incident natural light is [tex]I = 1000 W/cm^2[/tex]

Generally a  linear polarizer divides the irradiance of a natural light by 2

  So For the first polarizer the irradiance of the natural light would become

              [tex]I_1 = \frac{I}{2}[/tex]

Substituting values

             [tex]I_1 = \frac{1000}{2}[/tex]

                 [tex]=500 \ W/cm^2[/tex]

Now looking at the question we can deduce that the angle between the transmission axis of the and second polarizer is

               [tex]\theta_d = \theta _2 - \theta_1[/tex]

Substituting values

               [tex]\theta_d = 50^o - 0^o[/tex]

                    [tex]=50^o[/tex]

According to Malus Law the irradiance of light that would come out from  the second polarizer is obtained by this mathematical expression

      [tex]I(\theta_d) = I_1 cos^2(\theta_d)[/tex]

Substituting values

       [tex]I_2 = I(\theta_d) = 500 *cos (50)[/tex]

           [tex]=321.39 W/cm^2[/tex]

 When the third polarizer is inserted between the first and second polarizer, we have that

  The angle between the first  polarizer and the third polarizer is mathematically evaluated as

               [tex]\theta_d_1 = \theta_3 - \theta_1[/tex]

Substituting the values

             [tex]\theta_d_1 = 25^o -0^o[/tex]

                  [tex]= 25^o[/tex]

According to Malus Law the irradiance of light that would come out from  the third  polarizer is obtained by this mathematical expression

              [tex]I(\theta_d_1) = I_1 cos^2(\theta_d_1)[/tex]

              [tex]I(\theta_d_1) = I_1 cos^2 (25)[/tex]

Substituting values

             [tex]= 500 cos^2(25)[/tex]

              [tex]I_3 = I(\theta_d_1) = 410.69 W/cm^2[/tex]

The angle between the third polarizer and the  second polarizer is  mathematically evaluated as

               [tex]\theta_d_2 = \theta_2 - \theta_3[/tex]

Substituting the values

             [tex]\theta_d_2 = 50^o -25^o[/tex]                    [Note the third polarizer is placed at the

                  [tex]= 25^o[/tex]                                The middle of the first and second

                                                             polarizer

According to Malus Law the irradiance of light that would come out from  the second  polarizer is obtained by this mathematical expression

              [tex]I(\theta_d_2) = I_3 cos^2(\theta_d_2)[/tex]

              [tex]I(\theta_d_1) = I_3 cos^2 (25)[/tex]

Substituting values

             [tex]= 410.69 cos^2(25)[/tex]

              [tex]I_4 = I(\theta_d_1) = 337.3 W/cm^2[/tex]