CBSE Class 12 Physics 2019 Outside Delhi Set 1 Paper

Question : 22 of 27

Marks: +1, -0

A triangular prism of refracting angle

60^{∘}

is made of a transparent material of refractive index

\;{2}/{{√{3}}}

.
A ray of light is incident normally on the face

{\KL}

as shown in the figure. Trace the path of the ray as it passes through the prism and calculate the angle of emergence and angle of deviation.

Solution:

i_C

is the critical angle for the prism/material,

µ\;=\;{1}/{ sin \;i_C}

∴ \;\; sin \;i_C\;=\;{1}/{µ}=\;{{√{3}}}/{2}

⇒ \;\; i_C\;=60^{∘}

Angle of incidence at face

{\AC}

of the prism

=60^{∘}

Hence, refracted ray grazes the surface AC.

⇒ \;\text " Angle of emergence "\;=90^{∘}

⇒ \;\text " Angle of deviation "\;\;=30^{∘}

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