Q.

An air bubble of radius 0.1 cm lies at a depth of 20 cm below the free surface of a liquid of density 1000 kg/m3. If the pressure inside the bubble is 2100 N/m2 greater than the atmospheric pressure, then the surface tension of the liquid in SI unit is (use g = 10 m/s2)          [2025]

1 0.02  
2 0.1  
3 0.25  
4 0.05  

Ans.

(4)

P1=P0+pgh=P0+1000×10×20100

 P1=P0+2000

So, P2P1=2TR=(2T1×103)

 P2=P0+2100   (given)

So, P0+2100P02000=2T×103

100=2T×103

 T=(120)=0.05 N/m