Q.

A soap bubble, having radius of 1 mm, is blown from a detergent solution having a surface tension of 2.5×10-2N/m. The pressure inside the bubble equals that at a point Z0 below the free surface of water in a container. Taking g=10m/s2, density of water =103kg/m3, the value of Z0 is          [2019]

1 0.5 cm  
2 100 cm  
3 10 cm  
4 1 cm  

Ans.

(4)

The pressure at a point Z0 below the surface of water, PZ0=P0+ρgZ0

Also, pressure inside a soap bubble, P=P0+4TR

As per question, PZ0=P         P0+4TR=P0+ρgZ0

Z0=4TRρg=4×2.5×10-21×10-3×103×10=1×10-2m=1 cm