When a glass slab is placed on a cross made on a sheet, the cross appears to be raised by `1cm`. The thickness of the glass is `3cm`. The critical angle for glass is

Options

A. `sin^(-1)(0.33)`
B. `sin^(-1)(0.5)`
C. `sin^(-1)(0.67)`
D. `sin^(-1)((sqrt(3))/(2))`

Answer

C

Explanation

We can write shift, `1=3(1-(1)/(mu))`
`implies 1-(1)/(mu)=(1)/(3)`
`implies mu=(3)/(2)`, Now using `(1)/(sini_(c))=(3)/(2)impliessini_(c)=(2)/(3)`
`implies i_(c)=sin^(-1)(0.67)`, where `i_(c)` is the critical angle.