Question:
A spherical balloon of radius $3 \mathrm{~cm}$ containing helium gas has a pressure of $48 \times 10^{-3}$ bar. At the same temperature, the pressure, of a spherical balloon of radius $12 \mathrm{~cm}$ containing the same amount of gas will be____________ $\times 10^{-6} \mathrm{bar}$.
Solution:
(750)
At constant temperature and number of moles
$P_{1} V_{1}=P_{2} V_{2}$
$P_{1}=48 \times 10^{-3} \mathrm{bar} ; V_{1}=\frac{4}{3} \pi(3)^{3}$
$V_{2}=\frac{4}{3} \pi(12)^{3}$
$P_{2}=\frac{P_{1} V_{1}}{V_{2}}=\frac{48 \times 10^{-3} \times(3)^{3}}{(12)^{3}}$
$=\frac{48 \times 10^{-3}}{64}=7.5 \times 10^{-4}=750 \times 10^{-6} \mathrm{bar}$