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 coalece under isothermal conditions then the radius of the new bubble is

• A. 2.3 cm
• B. 4.5 cm
• C. 5 cm
• D. 7 cm

Answer 1

The correct option is C 5 cm

Since the pressure inside the bubble

$P_{net}=P_a+P_b$

$\frac{4T}{R}\times \frac{4}{3}\pi R^3=\frac{4T}{r_1}\times \frac{4}{3}\pi r_1^3+\frac{4T}{r_2}\frac{4}{3}\pi r_2^3$

$R^2=r_1^2+r_2^2=3^2+4^2$

$R=5cm$