Question

A soap bubble in vacuum, has a radius of $3$cm and another soap bubble in vacuum has a radius of $4$cm. If the two bubbles coalesce under isothermal condition, then the radius of new bubble is :

• A. $4.3$cm
• B. $4.5$cm
• C. $5$cm
• D. $7$cm

Answer 1

The correct option is B $4.5$cm

Total volume is conserved.
$\therefore \frac{4\pi }{3}(3{)}^3+\frac{4\pi }{3}(4{)}^3=\frac{4\pi }{3}{R}^3$
or $R\equiv 4.5$cm.