An observer can see through a pin-hole the top end of a thin rod of height h, placed as shown in

Doubtnut

An observer can see through a pin-hole the top end of a thin rod of height h, placed as shown in the figure. The height of beaker is `3h` and its radius is h. When the beaker is filled with a liquid up to a height `2h`, he can see the lower end of the rod. Then the refractive index of the liquid is

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