CBSE Class 12 · 2014 · Geometrical OpticsShort Answer

Two monochromatic rays of light are incident normally on the face

A B

of an isosceles right-angled prism

A B C

. The refractive indices of the glass prism for the two rays `1' and `2' are respectively

1.38

and

1.52

. Trace the path of these rays after entering through the prism.

Solution

Both rays enter normally through

A B

and strike the hypotenuse

A C

4 5^{\circ}

. TIR occurs if

sin 4 5^{\circ} > \frac{1}{μ}

, i.e.

μ > 2 \approx 1.414

∙

Ray 1:

μ = 1.38 < 1.414 \Rightarrow 4 5^{\circ} < θ_{c}

, the ray \emph{refracts out} of face

A C

∙

Ray 2:

μ = 1.52 > 1.414 \Rightarrow 4 5^{\circ} > θ_{c}

, the ray is \emph{totally internally reflected} at

A C

and leaves through

B C

CBSE Class 12 Board · 2014 · Subjective