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Multiple choice physics fluid pressure pressure in air introduction to atmospheric pressure pressure exerted by air devices to measure pressure

An air tight container having a lid with negligible mass and a area of $8 c m^{2}$ is partially evacuated . If a 40N force is require to pull a lid off the container and the atmospheric pressure is $ 1.0 \times 10^{5} \mathrm{Ps}$ ,the presure in the container before it is opened must be

  1. 0.6atm

  2. 0.5atm

  3. 0.4atn

  4. 0.2atm
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
The pressure inside the container must be equal to the pressure developed by force applied and the atmospheric force would oppose the pull,

So,

$P _{external}=P _{inside}+P _{atmosphere}$

$=\dfrac{48}{0.008}=P _{inside}+1\times 10^5$

$P _{inside}=0.6\times 10^5-1\times 10^5$

$P _{inside}=-0.4\times 10^5\,Ps=0.4\,atm$

Multiple choice physics fluid pressure pressure in air introduction to atmospheric pressure pressure exerted by air devices to measure pressure

A gas is collected over the water at $25 ^ { \circ } \mathrm { C }$ . The total pressureof moist gas was 735$\mathrm { mm }$ of mercury. If the aqueous vapourpressure at $25 ^ { \circ } \mathrm { C }$ is 23.8$\mathrm { mm }$ . Then the pressure of dry gas is

  1. $760$ $\mathrm { mm }$

  2. $758.8$ $\mathrm { mm }$

  3. $710.8$ $\mathrm { mm }$

  4. $711.2$ $\mathrm { mm }$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The pressure of dry gas is calculated by subtracting the aqueous vapor pressure from the total pressure of the moist gas. Pressure_dry = Total_pressure - Vapor_pressure = 735 mm - 23.8 mm = 711.2 mm.

Multiple choice physics fluid pressure pressure in air introduction to atmospheric pressure pressure exerted by air devices to measure pressure

20$\mathrm { cm }$ containing mercury and two equal ends containing air at standardatmospheric prossure. If the tube is now turned to a vertical position, by what amount will the mercury bo displaced?
(Given : cross-section of the tube can be assumed to be uniform):

  1. 2.95$\mathrm { cm }$

  2. 5.18$\mathrm { cm }$

  3. 8.65$\mathrm { cm }$

  4. 0.0$\mathrm { cm }$
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice physics fluid pressure pressure in air introduction to atmospheric pressure pressure exerted by air devices to measure pressure

The height of mercury column in a simple barometer is h. As the tube is inclined to the vertical at an angle $  \alpha,  $ the length of mercury column along the length of the tube is l; then:

  1. $ 1=\frac{h}{\cos \alpha} $

  2. $ 1=h \cos \alpha $

  3. $ I=h $

  4. $ 1=\cos \alpha / h $
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In a barometer, the vertical height h is the projection of the length l of the mercury column along the tube. Thus, h = l * cos(alpha), which rearranges to l = h / cos(alpha).

Multiple choice physics fluid pressure pressure in air introduction to atmospheric pressure pressure exerted by air devices to measure pressure

If the intensity of the incident radio wave of  $1\mathrm { w } / \mathrm { w } ^ { 2 }$  is reflected by the surface, find the pressure exerted on the surface?

  1. $5.67 \times 10 ^ { - 9 } N / m ^ { 2 }$

  2. $6.67 \times 10 ^ { - 9 } N / m ^ { 2 }$

  3. $8.67 \times 10 ^ { - 9 } N / m ^ { 2 }$

  4. $9.67 \times 10 ^ { - 8 } \mathrm { N } / \mathrm { m } ^ { 2 }$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For reflecting surface, Pressure

$\begin{array}{l} =\frac { { 2F } }{ C }  \ =\frac { { 2\times 1 } }{ { 3\times { { 10 }^{ 8 } } } } =6.67\times { 10^{ -9 } }N/{ m^{ 2 } } \ Ans.\, \, (B) \end{array}$

Multiple choice physics fluid pressure pressure in air introduction to atmospheric pressure pressure exerted by air devices to measure pressure

Which limb of the tube should be connected to the pump?

  1. Limb having radius 2 mm

  2. Limb having radius 1 mm

  3. Any of the climb

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The pressure difference due to surface tension in a capillary tube is delta_P = 2 * T / R. To minimize the pressure required to move the meniscus or to control the flow, the limb with the smaller radius (higher capillary pressure) is typically connected to the pump.