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NEET 2019 · Excess Pressure: Drops & Bubbles

Excess Pressure: Drops & Bubbles question from NEET 2019

Q54NEET 2019Easy

Excess Pressure: Drops & Bubbles

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

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Answer: (a)

  1. Excess pressure in the bubble ΔP=4TR=4×2.5×10−210−3=100\Delta P = \frac{4T}{R} = \frac{4 \times 2.5 \times 10^{-2}}{10^{-3}} = 100 Pa.
  2. At depth Z0Z_0 in water, pressure =P0+ρgZ0= P_0 + \rho g Z_0, so ρgZ0=100\rho g Z_0 = 100.
  3. Z0=100103×10=0.01Z_0 = \frac{100}{10^3 \times 10} = 0.01 m
  4. So the answer is (a) 1 cm.
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