JEE Main | 2014Momentum and CollisionHard
Question
On heating water, bubbles being formed at the bottom of the vessel detatch and rise. Take the bubbles to be spheres of radius R and making a circular contact of radius r with the bottom of the vessel. If r << R, and the surface tension of water is T, value of r just before bubbles detatch is (Density of water is ρw)
Options
A.R2
B.
C.
D.
Solution
When the bubble gets detached,
Buoyant force = force due to surface tension
∫ T × dl sin θ =
π R3 ρwg⇒ T × 2πr ×
π R3 ρwg⇒ r2 =
⇒ r = R2
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