ok....this is a very nice Q. provided that ur solving this one for the first time.....

there's a glass cube of edge length 'a'.......and made of material of refractive index  .......there's a dust particle placed at the geometrical centre of the cube........wats the amount of area that ill have to cover on the surface of the cube so that i am not able to see the dust particle from outside..........

im telling u.....ull feel good after solving this one.......

thanx ..

sumtimes questions need to be appreciated as welll

a^2/4(n^2-1) on each face

where n is refractive index

this was a good Q. and a good answer.........

oops!!! u missed a pi i guess........

neways im satisfied with ur answer .......

so mr mukund madhav how did u find the prob..........

dekho yaar........as u can see in the picture........any ray that goes for an angle of incidence beyond $ will be totally internally reflected........toh i will have to block all the rays at an angle of incidence of less than $......

but $= cosecinverse (n).........

so using this and edge lenght as a we can find out the base of the cone....and thus the area.......

ie area =pi R2

but R=a/2 tan $

and $= cosecinverse(n)....

so using all these informations we can get the reqd. result.....