The amount of work done in blowing a soap bubble such that its diameter increases from d to D is (T= surface tension of the solution)

(a) $4\mathrm{\pi }\left({\mathrm{D}}^{2}-{\mathrm{d}}^{2}\right)\mathrm{T}$                     (b) $8\mathrm{\pi }\left({\mathrm{D}}^{2}-{\mathrm{d}}^{2}\right)\mathrm{T}$

(c) $\mathrm{\pi }\left({\mathrm{D}}^{2}-{\mathrm{d}}^{2}\right)\mathrm{T}$                        (d) $2\mathrm{\pi }\left({\mathrm{D}}^{2}-{\mathrm{d}}^{2}\right)\mathrm{T}$

(d)

$\mathrm{W}=\mathrm{T}×8\mathrm{\pi }\left({\mathrm{r}}_{2}^{2}-{\mathrm{r}}_{1}^{2}\right)=\mathrm{T}×8\mathrm{\pi }\left(\frac{{\mathrm{D}}^{2}}{4}-\frac{{\mathrm{d}}^{2}}{4}\right)\phantom{\rule{0ex}{0ex}}=2\mathrm{\pi }\left({\mathrm{D}}^{2}-{\mathrm{d}}^{2}\right)\mathrm{T}$

Difficulty Level:

• 8%
• 37%
• 16%
• 40%