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  • Surface tension of a soap bubble is 2.0 × 10–2 Nm–1 . Work done to increase the radius of soap bubble from 3.5cm to 7 cm will be: Take <img

Surface tension of a soap bubble is 2.0 × 10–2 Nm–1 . Work done to increase the radius of soap bubble from 3.5cm to 7 cm will be:
Take \left [\pi =\frac{22}{7} \right ]

Option: 1

9.24 × 10–4 J 


Option: 2

5.76 × 10–4 J 


Option: 3

0.72 × 10–4 J 


Option: 4

18.48 × 10–4 J


Answers (1)

\begin{aligned} & \mathrm{T}=2.0 \times 10^{-2} \mathrm{Nm}^{-1} \\ & \mathrm{r}_1=3.5 \mathrm{~cm}, \mathrm{r}_2=7 \mathrm{~cm} \\ & \mathrm{~W}=\mathrm{T} \Delta \mathrm{A} \times \mathrm{No} . \text { of air }- \text { liquid surface } \\ & \mathrm{W}=2 \mathrm{~T} .4 \pi\left(\mathrm{r}_2^2-\mathrm{r}_1^2\right) \\ & \mathrm{W}=2 \times 2 \times 10^{-2} \times 4 \pi\left[49-\frac{49}{4}\right] \times 10^{-4} \\ & \mathrm{~W}=16 \pi \times 10^{-6} \times 49 \times \frac{3}{4} \\ & \mathrm{~W}=1847.26 \times 10^{-6} \\ & \mathrm{~W}=18.47 \times 10^{-4} \mathrm{~J} \end{aligned}

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