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Properties of Matter question

2025 · 23 Jan · Shift 2 · Q73
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Properties of Matter question

2025 · 23 Jan · Shift 2 · Q73

JEE MainPhysicsProperties of MatterNumerical+4 / −1
An air bubble of radius 1.0 mm is observed at a depth 20 cm below the free surface of a liquid having surface tension 0.095 J/m20.095 \mathrm{~J} / \mathrm{m}^20.095 J/m2 and density 103 kg/m310^3 \mathrm{~kg} / \mathrm{m}^3103 kg/m3. The difference between pressure inside the bubble and atmospheric pressure is ‾N/m2\underline{\hspace{2cm}}\mathrm{N} / \mathrm{m}^2​N/m2. (Take g=10 m/s2\mathrm{g}=10 \mathrm{~m} / \mathrm{s}^2g=10 m/s2 )
Numerical answer
View written solutionFree

Correct answer: 2190

  1. Given data
  • Radius of air bubble: r=1.0 mm=1.0×10−3 mr = 1.0\text{ mm} = 1.0 \times 10^{-3}\text{ m}r=1.0 mm=1.0×10−3 m
  • Depth below liquid surface: h=20 cm=0.20 mh = 20\text{ cm} = 0.20\text{ m}h=20 cm=0.20 m
  • Surface tension: T=0.095 N/mT = 0.095\text{ N/m}T=0.095 N/m
  • Density of liquid: ρ=103 kg/m3\rho = 10^3\text{ kg/m}^3ρ=103 kg/m3
  • Acceleration due to gravity: g=10 m/s2g = 10\text{ m/s}^2g=10 m/s2

We need:

Pinside−PatmP_{\text{inside}} - P_{\text{atm}}Pinside​−Patm​

  1. Pressure outside the bubble

At depth hhh in a liquid, the pressure is:

Poutside=Patm+ρghP_{\text{outside}} = P_{\text{atm}} + \rho g hPoutside​=Patm​+ρgh

So,

ρgh=(103)(10)(0.20)=2000 N/m2\rho g h = (10^3)(10)(0.20) = 2000\text{ N/m}^2ρgh=(103)(10)(0.20)=2000 N/m2

Hence,

Poutside=Patm+2000P_{\text{outside}} = P_{\text{atm}} + 2000Poutside​=Patm​+2000

  1. Excess pressure inside an air bubble in a liquid

For an air bubble in a liquid, there is only one liquid surface, so excess pressure is:

Pinside−Poutside=2TrP_{\text{inside}} - P_{\text{outside}} = \frac{2T}{r}Pinside​−Poutside​=r2T​

Substitute values:

2Tr=2(0.095)1.0×10−3=0.1910−3=190 N/m2\frac{2T}{r} = \frac{2(0.095)}{1.0 \times 10^{-3}} = \frac{0.19}{10^{-3}} = 190\text{ N/m}^2r2T​=1.0×10−32(0.095)​=10−30.19​=190 N/m2

  1. Pressure inside bubble relative to atmospheric pressure

Pinside−Patm=(Poutside−Patm)+(Pinside−Poutside)P_{\text{inside}} - P_{\text{atm}} = (P_{\text{outside}} - P_{\text{atm}}) + (P_{\text{inside}} - P_{\text{outside}})Pinside​−Patm​=(Poutside​−Patm​)+(Pinside​−Poutside​)

=2000+190=2190 N/m2= 2000 + 190 = 2190\text{ N/m}^2=2000+190=2190 N/m2

  1. Final answer

2190 N/m2\boxed{2190\text{ N/m}^2}2190 N/m2​

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