A beam of light consisting of red, green and blue colours is incident on a right angled prism. The refractive index of the material of the prism for the above red, green and blue wavelengths are 1.39, 1.44 and 1.47, respectively.


The prism will:

  • Option 1)

    separate all the three colours from one another

  • Option 2)

    not separate the three colours at all

  • Option 3)

    separate the red colour part from the green and blue colours

  • Option 4)

    separate the blue colour part from the red and green colours

 

Answers (1)

As we learnt in 

Critical angle -

sin c = Refractive index of rarer medium / Refractive index of denser medium

- wherein

When angle of incidence of a travelling from a dence medium to rarer medium is greater than critical angle, no refraction occurs.

 angle of incidence at surface AC= 45^{\circ}

Critical Angle of incidence

sin\ c=\frac{1}{\mu}

For red \mu_r=1.39

For green \mu_g=1.44

For blue \mu_b=1.47

Since refractive index of green and blue is greater than \sqrt{2} and hence their critical angles are less than 45^{\circ}

So green and blue will be completely reflected while red will emerge out of prism. Hence red will be separated from green and blue.

 

 


Option 1)

separate all the three colours from one another

Option 2)

not separate the three colours at all

Option 3)

separate the red colour part from the green and blue colours

Option 4)

separate the blue colour part from the red and green colours

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