Mole of an ideal gas is contained in a cubical volume V, ABCDEFGH at 300 K (figure). One face of the cube (EFGH) is made up of a material which totally absorbs any gas molecule incident on it .At any given time.

Options

A. the pressure on EFGH would be zero
B. the pressure on all the faces will be equal
C. the pressure on EFGH would be double the pressure on ABCD
D. the pressure on EFGH would be half that on ABCD

Answer

D

Explanation

When a moving molecule colloides elastically with the wall of the container, the momentum transformed by the molecule to the wall = mv - (-mv) = 2mv.
Force exerted by the molecule on the wall = Rate of change of momentum and pressure `="Force"/"Area"`.
This is for a normal surface of the cube.
But only the face EFGH is a totally absorbing surface. Hence only the momentum mv is transformed to it (instead of 2mv for the other surfaces).
`therefore` The pressure on EFGH = `1/2` of the pressure on ABCD.