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he rubber tube of a bicycle tyre is inflated to an absolute pressure P. Consider

ID: 700826 • Letter: H

Question

he rubber tube of a bicycle tyre is inflated to an absolute pressure P. Considering that the loss of pressure with time is due to the diffusion of N; and Oz through the rubber tube, the time it takes for the pressure to reduce to P is given by the following equation, assuming that the diffusions follows Fick's law with a linear profile through the tube wall and an effective diffusion coefficient Das. The surface area, volume and rubber wall thickness of the tube are S m. V m2 and w respectively. The atmospheric pressure outside the tube is Po In an experiment, the tube is placed inside a pressure container and as the pressure in the tube is falling from Pi to Pz the container pressure is raised to P2. In this case the time, t, taken for the pressure to fall to Pz is: A Halved B Equal to wV/S DA C Indeterminate D Infinity

Explanation / Answer

Inside the pressure container

The pressure in tube P2 approaches to pressure inside the container P2.

In the given equation, we can replace the atmospheric pressure outside of the tubes P0 from P2

The logarithmic part will vanish and the time taken

t = wV/SDAB

OPTION B IS THE CORRECT ANSWER