A diver at a depth of 12 cm, ses the sky in a cone of semi-vertical angle :
Given,
The refractive index water is μw=43
From the figure it can be seen that ray coming out of water making an angle as r=90∘
Applying Snell’s law of refraction
μwsinθ=μasin90∘
Where μa=1 and μw=43
Therefore,
43sinθ=1⇒sinθ=34
∴θ=sin−1(34)