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 $\rho_{w}$ )

• A. $R^{2}\sqrt{\frac{2 \rho_{w}\,g}{3T}}$
• B. $R^{2}\sqrt{\frac{\rho_{w}\,g}{6T}}$
• C. $R^{2}\sqrt{\frac{\rho_{w}\,g}{T}}$
• D. $R^{2}\sqrt{\frac{3\rho_{w}\,g}{T}}$

Answer 1

Answer: (A)

$R^{2}\sqrt{\frac{2 \rho_{w}\,g}{3T}}$

Answer 2

When the bubble gets detached, Buoyant force = force due to surface tension