GATE 2022 MT – Question 47
A gas bubble of radius 0.01 mm is trapped in molten steel at 1773 K. External pressure is 1.5 bar and surface tension at this temperature is 1.4 N/m. Given 1 bar $=10^5$ Pa, its internal pressure is ______ bar (one decimal place).
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Correct answer: 4.3 to 4.3
Explanation
For one spherical gas–liquid interface, $\Delta P=2\gamma/r$. With $r=10^{-5}$ m, $\Delta P=2(1.4)/10^{-5}=2.8\times10^5$ Pa = 2.8 bar. Add 1.5 bar external pressure: **4.3 bar**.