A concave mirror is placed at the bottom of an empty tank with face upward and axis vertical. When sunlight falls normally on the mirror, it is focused at distance of \(32\ cm\) from the mirror. If the tank filled with water \(\left(\mu =\dfrac{4}{3} \right)\) upto a height \(20\ cm\) then the sunlight will now get focused at
1
\(16\ cm\) above water level
2
\(9\ cm\) above water level
3
\(24\ cm\) below water level
4
\(9\ cm\) below water level