Question

$1$ mole of an ideal gas is contained in a cubical volume $V$, $ABCDEFGH$ at $300 \,K$ as shown in 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,

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

Answer 1

Answer: (D)

The pressure on face $EFGH$ would be half that on face $ABCD$. This is because force $EFGH$ absorbs totally all the molecules incident on it. These molecules do not rebound. Change in momentum causing force and hence pressure is reduced to half compared to force//pressure on face $ABCD$ from where molecules rebound with an equal velocity.