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9.2 , surface tension — Physics STD 11 Science — Question

Rajasthan BoardEnglish MediumSTD 11 SciencePhysics9.2 , surface tension1 Mark
MCQ
A soap bubble of radius $R$ is blown. After heating the solution a second bubble of radius $2R$ is blown. The work required to blow the second bubble in comparison to that required for the first bubble is
  • A
    Double
  • B
    Slightly less than double
  • ✓
    Slightly less than four times
  • D
    Slightly more than four times
✓

Answer

Correct option: C.
Slightly less than four times
c
(c) Work done to form a bubble of radius $R$

${W_1} = 8\pi {R^2}{T_1}$

Work done to form a bubble of radius $2R$

${W_2} = 8\pi {(2R)^2}{T_2}$$ = 32\pi {R^2}{T_2}$ ?$\frac{{{W_1}}}{{{W_2}}} = \frac{{{T_1}}}{{4{T_2}}}$

If surface tension of soap solution is same then

${W_2} = 4{W_1}$

But in the problem temperature of solution is increased so its surface tension decreases.

$\therefore {W_2} < 4{W_1}$

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