Question

A spherical soap bubble of radius 2 cm attached to the outside of a spherical bubble of radius 4 cm. Then what is the radius of the common surface? 

(A) 3.5 cm 

(B) 4 cm 

(C) 4.5 cm 

(D) 3 cm

Answer 1

The correct option is (B) 4 cm.

Explanation:

For bubble P = (4T / r)

 ∴ P₂ – P₁ = (4T / r₂) – (4T / r₁) = 4T [(1 / r₂) – (1 / r₁)]

hence (1 / r) = (1 / r₂) – (1 / r₁)

∴ (1/r) = (1/2) – (1/4) = (1/4) 

∴ r = 4 cm