Question

A soap bubble of radius $\sqrt{7}$cm is blown. Work done in this process is used to store energy in capacitor at potential of $1$V using transducer. Charge stored is ________.

$(T=30dyne/cm)$

• A. $5.28\mu C$
• B. $10.56\mu C$
• C. $21.12\mu C$
• D. $21.12mC$

Answer 1

Answer: (B)

$10.56\mu C$

Change in energy of the soap bubble $=\Delta A\times T$.
Change in Area $=2\times 4\pi R^2$, (as the soap bubble has two surfaces).
Change in Energy $=2\times 4\pi \times 7\times 30ergs$
Thus, Energy of the capacitor $=$ work done on the bubble.

$\frac{1}{2}QV=2\times 4\pi \times 7\times 30\times {10}^{-9}$

$Q=10.56\mu C$