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A rectangulat block of refractive index ...

A rectangulat block of refractive index `mu` is placed on a printed page lying on a horizontal surface as shown in Fig. , Find the minimum value of `mu` so that the letter L on the page is not visible from any of the vertical sides.

Text Solution

Verified by Experts

The letter L will not be visible from the vertical sides if the light ray does not enter through it.
We can apply the condition of no emergenc for a prism of angle `A=90^(@)` .
That is `mu gt (1)/(" sin "(A)/(2)` or `mu gt (1)/(" sin "(90^(@))/(2)` or `mu gt sqrt2`
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