A rectangulat block of refractive index `mu` is placed on a printed page lying on a horizontal surface as shown in Fig. , Find the minimum value of `mu` so that the letter L on the page is not visible from any of the vertical sides.

Explanation

`sinC=1//mu`
`DeltaABC`, `i_0+C=90^@impliesi_0=90^@-C`
For T.I.R. on vertical face
`i_0geC`
`(90^@-C)geC`
`90^@ge2C`
`45^@geC`
`sin45^@gesinC`
`1/sqrt2ge1/mu`
`mugesqrt2`
`mu_(min)=sqrt2`