Question

Work done in blowing a soap bubble of radius $R$ is $W$. The additional amount of work done to increase its radius to $\sqrt{3}R$ is :

• A. $3W$
• B. $2W$
• C. $W$
• D. $\frac{W}{3}$

Answer 1

The correct option is B $2W$

Let,

$T=$ surface tension

$R=$ radius of soap

Work done, $W=T.\pi R^2$

Now, $R^{\prime }=\sqrt{3}R$

Work done,

$W^{\prime }=T.\pi 3R^2$

$W^{\prime }=3W$

Additional work done, $\delta W=3W-W=2W$

The correct option is B.