A small air bubble (cavity of air) of radius `'h'`. Find the pressure inside the bubble.

Explanation

Out of water and air (inside the bubble) air is on concave part.

Pressure excess inside a liquid bubble kept in air :-

So pressure inside the liquid bubble `= P_(0) + (4T)/(r)`
So pressrue excess inside the liquid bubble `= (4T)/(r)`
Alternaltive method :-
Draw free body diagram of half part of bubble. The force on this hemisphere are :
`(i)` Pushing force on the left half liquid due to right half liquid will be `(P_("in"))(pir^(2))`
`(ii)` Pushing force due to atmospheric pressure will be `(P_(0)) xx ("facing area") = P_(0) (pir^(2))`
`(iii)` Surface tension force on both inner and outer surface will be `(T)(2pir) xx 2`
Applying force balance
`(P_("in"))(pir^(2)) = P_(0)(pir^(2)) + (T)(2pir) xx 2 rArr P_("in") = P_(0) + (4T)/(r)`, So pressure excess inside a liquid bubble `= (4T)/(r)`