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JEE Main 202117 MarchMorning Shift
Exam
JEE Main
Year
2021
Date
17 March
Shift
Morning Shift
Subject
Physics
Chapter
Mechanical Properties of Fluids

JEE Main 2021 · 17 March · Morning Shift · Physics · Mechanical Properties of Fluids

When two soap bubbles of radii a and b ( b > a ) coalesce, the...

When two soap bubbles of radii aa and bb(b>a)( b > a ) coalesce, the radius of curvature of common surface is:

Options

  1. Aabb−a\dfrac{ab}{b - a}
  2. Ba+bab\dfrac{a + b}{ab}
  3. Cb−aab\dfrac{b - a}{ab}
  4. Daba+b\dfrac{ab}{a + b}

Correct answer

A. abb−a\dfrac{ab}{b - a}

Step-by-step solution

Excess pressure at common surface is given by

Pex=4T(1a−1b)=4Tr{P}_{ex} = 4T\left(\dfrac{1}{a} - \dfrac{1}{b}\right) = \dfrac{4T}{r}

∴1r=1a−1b∴ \dfrac{1}{r} = \dfrac{1}{a} - \dfrac{1}{b}

r=abb−ar = \dfrac{ab}{b - a}

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