# Pressure needed to reduce size of soap bubble by half

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cylinder with the movable system contains air under pressure $p_1$and a soap bubble of radius R .
The pressure $p_2$to which the air should be compressed by slowly pushing the Piston into the cylinder for the soap bubble to reduce its size by half.
( the surface tension is T and temperature is maintained constant)

I tried it as $4T / R = p_i - p_1$

Then $4T / ( R/2) = p_i' - p_2$

where $p_i$ = internal pressure
and $p_i'$ = new internal pressure

From here I am unable to do as no relation for $p_i$ and $p_i'$

The answer given is $8 p_1 + 24T/R$ ;