A pile 4m high driven into the bottom of a lake is 1m above the `
`water . Determine the length of the shadow of the pile on the bottom of the lake if `
` the sun rays make an angle of `45^@` with the water surface . The refractive index`
` if water is `4/3`. `

Explanation

From Snell's law,
`4/3=(sin45^(@))/(sinr)`

Solving this equation, we get, `r=32^(@)`
Further, EF=(DE) tan `32^(@)`=1.88 m
`therefore` Total length of shadow, L=CF
or L=(1+1.88) m =2.88 m
The thickness of the cube =t=9.0 cm. The shift in the position of the printed letters is
`Deltad=(1-1/mu)d=(1/1-1.5)xx9.0 cm=3.0 cm`