# 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 m

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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.

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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`