Courses
Courses for Kids
Free study material
Offline Centres
More
Store Icon
Store

Find neon pressure in the manometer, when atmospheric pressure is 650 torr.

A) 665 torr
B) 80 torr
C) 570 torr
D) 650 torr

seo-qna
Last updated date: 20th Jun 2024
Total views: 55.5k
Views today: 0.55k
Answer
VerifiedVerified
55.5k+ views
Hint: Manometer is a device that works on the principle of hydrostatic equilibrium. Hydrostatic equilibrium states that the pressure at any point in a fluid at rest is equal, and its value is just the weight of the overlying liquid.

Complete step by step answer:
Moving back to the question figure, we can see that height h of the manometric fluid column above point A is,
$h = 49\;{\rm{cm}} - 39\;{\rm{cm}}$
$ \Rightarrow h = 8\;{\rm{cm}} \times \dfrac{{10\;{\rm{mm}}}}{{1\;{\rm{cm}}}}$
$ \Rightarrow h = 80\;{\rm{mm}}$
Since point A and B are at the same levels, therefore the pressure at point A and B is the same, and it can be written as,
$ \Rightarrow {P_A} = {P_B}$
Now, the pressure at point A can also be written as the sum of the pressure of neon gas and the pressure to manometric fluid column h. Therefore,
$ \Rightarrow {P_{Ne}} + h = {P_A}$ …… (I)
Here ${P_{Ne}}$ is the pressure due to neon gas.
But since ${P_A} = {P_B}$ therefore the equation (I) becomes,
$ \Rightarrow {P_{Ne}} + h = {P_B}$ …… (II)
Since point B is open to atmosphere and therefore, the pressure at point B is equal to the atmospheric pressure, i.e. ${P_B} = 650\;{\rm{torr}}$.
We will now substitute ${P_B} = 650\;{\rm{torr}}$ and $h = 80\;{\rm{mm}}$ in equation (II), and therefore it becomes,
$ \Rightarrow {P_{Ne}} + 80\;{\rm{mm}} = 650\;{\rm{torr}} \times \dfrac{{1\;{\rm{mm}}}}{{1\;{\rm{torr}}}}$
$ \Rightarrow {P_{Ne}} + 80\;{\rm{mm}} = 650\;{\rm{mm}}$
$ \Rightarrow {P_{Ne}} = 570\;{\rm{mm}} \times \dfrac{{1\;{\rm{torr}}}}{{1\;{\rm{mm}}}}$
$ \Rightarrow {P_{Ne}} = 570\;{\rm{torr}}$

Therefore, the neon pressure in the manometer is 570 torr, and the correct option is (C).

Note: Since we have seen how a manometer is used, let us know some more applications of a manometer in daily life. In addition to straight pressure and vacuum measurement, other process variables that are a function of pressure can be readily measured with a manometer. Typical uses are flow, filter pressure drop, meter calibrations, leak testing and tank liquid level.