A bulb contains O2 at pressure P. The time taken for the pressure to fall to P/2 by effusion is t_1. If the bulb instead contains H2 at the same initial pressure and temperature, the time for the pressure to fall to P/2 is t_2. The ratio t_1 : t_2 is

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A bulb contains $O X_{2}$ at pressure $P$ . The time taken for the pressure to fall to $P /2$ by effusion is $t_{1}$ . If the bulb instead contains $H X_{2}$ at the same initial pressure and temperature, the time for the pressure to fall to $P /2$ is $t_{2}$ . The ratio $t_{1} : t_{2}$ is

The effusion rate is proportional to

p / M

, so the pressure decays with a time constant proportional to

M

. The time for the same fractional drop scales as

M

t_{1} / t_{2} = 32/2 = 4