Q: A small air bubble of 0.1 mm diameter is formed just below the surface of water. If surface tension of water is 0.072 Nm^{-1}, the pressure inside the air bubble in kilo Pascal is (Atmospheric pressure = 1.01 × 10^{5} pa)

(a) 28.9

(b) 0.289

(c) 0.0289

(d) 103.88

Ans: (d)

Sol: Pressure inside $ \displaystyle P_{in} = P_0 + \frac{2 S}{r} $

Since $ \displaystyle \frac{2 S}{r} = \frac{2\times 0.072}{0.1 \times 10^{-3}/2}= 2880 Pa = 2.88 kPa $

$ \displaystyle P_{in} = 101 + 2.88 $

= 103.88 kPa