In the figure ABC is the cross-section of a right angled prism and BCDE is the cross-section of a glass slab. The value of theta so that light incident normally on the face AB does not cross the face BC is `(Given sin^-1 3//5=37^@)`

Options

A. `thetale37^(@)`
B. `thetalt37^(@)`
C. `thetale53^(@)`
D. `thetalt53^(@)`

Answer

b.

Explanation

`A=90^(@)-theta`
`rArr r_(2)=A=90^(@)-theta gt theta_(c)`
`costheta gt sintheta_(c)=(6//5)/(2//3)=(4)/(5)`
`(theta_(C)` is critical angle)
`theta lt cos^(-1)(4)/(5)=37^(@)`