1.

A printed page is kept pressed by a transparent cube of edge t. The refractive index of the cube varies us mu (z) =1 + z /t, where x is the vertical distance from bottom of the cube. If viewed from top, then the printed letters appear to be shifted by an amount

Answer»

`(1-ln2) t `
` (2ln 2-1)t `
`(t)/(2ln2)`
`(2t)/(3ln2)`

Solution :
Condider an ELEMENTAL strip at a height z of thickness dz.
Apparent height =`("Real height ")/(RI)= (d)/(mu(z))`
`dh = (dz)/(1+ (z)/(t))`
`dh = ((t)/(t +z))dz`
`h INT _(0) ^(z) (t)/(t +z).dz`
`h = [t ln (t + z) ]_(0)^(2) =t [ln (1+ t) - ln (t+ 0)]`
`h = t ln ""(2t)/(t) = t ln 2`
Shift, `Deltax, = t- t ln2`
`implies Delta X = (1- ln 2) t `


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