Question

Derive an expression for the excess pressure inside a soap bubble ?

Answer 1

Heya,Im a new user (teacher of physics just came to know about this site and decided to help you!) 
Good question!
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Now time to unlock its answer!!
let atmospheric pressure=Po
pressure due to charge on bubbles(P)=¥^2/2€
where ¥ is surface charge density and € is permetivity of medium. 
now 
Pnet=Pi+P-Po
where Pi is initial pressure of bubble

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Pnet=Pi+P-Po
4T/r=(Pi-Po)+¥^2/2€
here T is surface tension in bubble and r is the radius of bubble .
(Pi-Po)=4T/r- ¥^2/2€
so,
excees pressure =4T/r- ¥^2/2€
because difference of initial pressure and atmospheric is known as excess pressure in bubble.
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