A ray of light is incident normally on one face of30^(@)-60^(@)-90^(@)prism of refractive index 5//3immersed in water of refractive index4//3as shown in figure.

A ray of light is incident normally on one face of30^(@)-60^(@)-90^(@)

1.	A ray of light is incident normally on one face of30^(@)-60^(@)-90^(@)prism of refractive index 5//3immersed in water of refractive index4//3as shown in figure.
Answer» The EXIT angle `theta_(2)`of the ray is `SIN^(-1)(5//8)` Total internal reflection at point `P`ceasesif the refractive index of water is increased to `5//2sqrt(3)`by dissolving some substance. Total internal reflection at point P ceases if the refractive index of water is increased to `5//2sqrt3` by dissolving some substance. Total internal reflection at point `P`ceases if the refractive index of water is increased to`5//6`by dissolving some substances. Solution : Taking refraction at surface `BC` `(5)/(3)xxsin30^(@)=(4)/(3)xx sintheta_(2)` `(5)/(3)xx(1)/(2)=(4)/(3)"sin"theta_(2)` `"sin"theta_(2)=(5)/(8) rArr theta_(2)=sin^(-1)(5)/(8)` For I.T.R.to happen at P `60^(@)gtC rArr sin60^(@)gtsin C......(1)` for C `(5)/(3) "sin"C=(3)/(5)mu_(w)xx sin90^(@) rArr mu_(w)=(5)/(3)Sin C` `sinC=(3)/(5)mu_(w)....(2)` `(SQRT(3))/(2)ge(3)/(5)mu_(w)` `(5)/(2sqrt(3))gemu_(w)`