A soap bubble, having radius of 1 mm, is blown from a detergent solution having a surface tension of 2.5 $ \times $ 10
–2
N/m. The pressure inside the bubble equals at a point Z
0
below the free surface of water in a container. Taking g = 10 m/s
2
, density of water = 10
3
kg/m
3
, the value of Z
0
is :