A tank is filled with a liquid of refractive index √ 2, up to a height of 30 cm. A tiny bulb is glowing at the bottom of the tank. Calculate the…

$\displaystyle \sin i_c = \dfrac{1}{\sqrt{2}}$$\displaystyle i_c = 45^{0}$$\displaystyle \tan i_c = \dfrac{r}{d}$$\displaystyle r = d \tan 45^{0}$$\displaystyle r = 30 \times 1 \ \text{cm}$$\displaystyle D = 2r = 60 \ \text{cm}$Alternatively:$\displaystyle D = 2r = \dfrac{2d}{\sqrt{n^{2}-1}}$$\displaystyle = \dfrac{2 \times 30}{\sqrt{\left(\sqrt{2}\right)^{2}-1}}$$\displaystyle D = 60\,\text{cm}$