Tag: pressure in air

Questions Related to pressure in air

To increase pressure, either force has to be increased or area of contact has to be decreased.

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

  1. True

  2. False

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Correct Option: A

By sucking through a straw, a student can reduce the pressure in his lungs to $750 mm$ of Hg (density = $\displaystyle 13.6{ gm }/{ { cm }^{ 3 } }$). Using the straw, he can drink water from a glass upto a maximum depth of: 

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

  1. $10 cm$

  2. $75 cm$

  3. $13.6 cm$

  4. $1.36 cm$

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Correct Option: C
Explanation:

Pressure difference created $= 10 mm$ of Hg 
This must be equal to the pressure of water column being created in the straw. If height of water column be $h$

$h \rho g = \dfrac{10}{10} \times 13.6 g$
$hg \times 1 = 13.6 g$
$h = 13.6 cm$

$1$ millibar is equal to a pressure of

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

  1. ${10}^{5}pa$

  2. $100pa$

  3. $1000pa$

  4. ${10}^{-3}pa$

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Correct Option: B
Explanation:

We know that $1$ bar $= 10^5 Pa$

So, $1$ millibar $=10^{-3}$ bar $=10^{-3}\times 10^5 Pa=100 Pa$

One gram mole of oxygen is enclosed in a vessel at a temperature of $27$ and at one atmospheric pressure. The vessel is thermally insulated and is moved with a constant speed $u _0$. Calculate $u _0$ if the rise in temperature is $1K$ when the vessel is suddenly stopped?

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

  1. $35.6 m/s$

  2. $45 m/s$

  3. $90 m/s$

  4. $60 m/s$

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Correct Option: B
Explanation:

since internal energy depends only on the temperature ,

as the temperature changes,
the change in internal energy is
$\Delta U= \dfrac{nfR \Delta T}{2}$

vessel contains a gas of mass M,
change in kinetic energy $= \dfrac{nMv^2}{2}$

$\dfrac{nfR \Delta T}{2}$= $\dfrac{nMv^2}{2}$

$\dfrac{2}{\dfrac{c _p}{c _v} - 1}$

$f = \dfrac{2}{\dfrac{2}{5}}$ = 5

putting value

$v = 45 m/s$

What will be the pressure in pascal due to a mercury column of $76$cm. Density of mercury is $13.6$ g$cm^2$, $g=980$ cm$s^2$?

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

  1. $1.0129\times 10^5$Pa

  2. $1.0129\times 10^4$Pa

  3. $1.0129\times 10^3$Pa

  4. $1.0129\times 10^2$Pa

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Correct Option: A
Explanation:

 h$=76cm$

Pressure=?

Formula to be used : $P=hgd$

Where h = height of mercury column and

 d= density of mercury$=13.6 gm/cc$

acceleration due to gravity$=980 cm/s²$

$P=hgd=13.6\times 980\times 76=1012928dyne.cm²$

The height of the mercury column in a simple barometer is $h$. As the tube is inclined with the vertical at an angle $\alpha$, the length of the mercury column along the length of the tube will become:

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

  1. $h\cos{\alpha}$

  2. $\dfrac{h}{\cos{\alpha}}$

  3. $h\sin{\alpha}$

  4. $\dfrac{h}{\sin{\alpha}}$

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Correct Option: B

Barometer was constructed by

physics pressure pressure in air introduction to atmospheric pressure devices to measure pressure

  1. Vermicelli

  2. Torricelli

  3. Archimedes

  4. Newton

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Correct Option: B
Explanation:

Barometer is a device used to measure atmospheric pressure. It was first constructed by Torricellli in the year 1643.

At sea level, the vertical height of mercury supported in the tube of simple barometer is ______ $cm$ above the mercury level in the bowl.
physics pressure in fluids and atmospheric pressure pressure in air introduction to atmospheric pressure devices to measure pressure

  1. $36$

  2. $76$

  3. $100$

  4. $7$

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Correct Option: B
Explanation:

The height to which mercury rises in simple barometer is $76cm$.

This is the reason that  atmospheric pressure is often expressed as $76cm$ of Hg at sea level.

Length of glass tube in simple barometer is
physics pressure in fluids and atmospheric pressure pressure in air introduction to atmospheric pressure devices to measure pressure

  1. $100\,mm$

  2. $1\,cm$

  3. $100\,cm$

  4. $1\,mm$

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Correct Option: C
Explanation:

A mercury barometer has a glass tube, of length approximately 100cm, closed at one end with an open mercury-filled reservoir at the base. 

The vacuum created in simple barometer is known as __________ vacuum
physics pressure in fluids and atmospheric pressure pressure in air introduction to atmospheric pressure devices to measure pressure

  1. Newton's

  2. Barometric

  3. Torricellian

  4. Archimedes

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Correct Option: C
Explanation:

A simple barometer or a mercury barometer has a glass tube closed at one end with an open mercury-filled reservoir at the base. The weight of the mercury creates a vacuum in the top of the tube known as Torricellian vacuum.