QJEEM14Ph3021: JEE Main 2014 Physics - Class 11 JEEM14Ph3021 Solution: On heating water, bubbles being formed at the bottom of the…

Question

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On heating water, bubbles being formed at the bottom of the vessel detach and rise. Take the bubbles to be spheres of radius

R

and making a circular contact of radius

r

with the bottom

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 detach is: (density of water is

ρ_{w}

)

Accepted Answer

When the bubble gets detached, Buoyant force

=

force due to surface tension
JEE Main 2014 (Offline) Physics - Properties of Matter Question 242 English Explanation

Force due to excess pressure

=

upthrust
Access pressure in air bubble

= \frac{2 T}{R}

\frac{2 T}{R} (π r^{2}) = \frac{4 π R^{3}}{3 T} ρ_{w} g

\Rightarrow r^{2} = \frac{2 R^{4} ρ_{w} g}{3 T}

\Rightarrow r = R^{2} \sqrt{\frac{2 ρ_{w} g}{3 T}}

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