a rectangular block of glass on a printed page is lying on a horizontal surface . find the minimum value of the refractive index of a glass for which the letters on the page are not visible from any of the vertical sides of the block???????

buddy wat i feel is the quest is incomplete.....

either its given that its a square block......... or a block wid gven lenghth and breadth....... so that we may find sin of angle..... maximium angle of incidence...........

thus we will impose restriction on that....... that is total internal reflection....... and find refractive index...........

Cheers!!!!!

I think so too...if its a square,then it easily works out to rt 2.

See,in the given figure, the black rays are the path of light.Only if the light gets totally internally reflected will the print be invisible.

The red line is the normal.

You know refractive index =sin i/sin r..

sin r =1 as r= 90..

sin i, as seen in figure(angle @ is angle i there..), is h/rt.(h²+l²)..

and we're stuck there..

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But if its a square, h=l

and sin i = refractive index = rt 2.

so please check the question..

if a blok of ABCD is considred the min. angle of incidence for which the ray gts tir at surface BC of  the given glass blok is 45degrees & hence 1/sinc vill be obviously =root2