A small air bubble in a sphere of glass with radius 4 cm appears to be 1 cm from the surface when observed along a diameter. Find the true positino of the air bubble.

Explanation

`(1)/(-1)-(mu)/(u)=(1-mu)/(-R)`
Put `R=4cm, mu=1.5` to get `u=4//3 cm` . So, the object is `4//3` cm away from the surface.