A cubical transparent slab is used as a paper weight. What should be the minimum refractive index of the material of the slab so that letters below it are not visible from any of its vertical faces.

A cubical block of glass is placed on a printed page lying on a horizontal surface. Then, the minimum value of refractive index of glass for which the letters on the page are not visible from any of the vertical faces of the block is

Word ‘Newton’s printed on a paper and is placed on a horizontal surface below a cubical glass. The minimum value of refractive index of a cubical glass for which letters are not visible from any vertical faces, of the glass, is (Critical angle =45°)

Light enters at an angle of incidence in a transparent rod of refractive index n. For what value of the refractive index of the material of the rod the light once entered into it will not leave it through its lateral face whatsoever be the value of angle of incidence.

Light enters at an angle of incidence in a transparent rod of refractive index n. For what value of the refractive index of the material of the rod the light once entered into it will not leave it through its lateral face whatsoever be the value of angle of incidence.