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Multiple choice physics pressure in liquids and gases common consequences of the atmospheric pressure atmospheric pressure and its consequences important points about atmospheric pressure

A barometer kept in an elevator reads $76\ cm$ when it is at rest. If the elevator goes up with some acceleration, the reading will be

  1. $76\ cm$
  2. $> 76\ cm$
  3. $< 76\ cm$

  4. Zero
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A barometer measures atmospheric pressure based on the weight of the mercury column. When an elevator accelerates upward, the effective gravity (g_eff = g + a) increases, which would normally increase the pressure reading; however, the mercury column itself also experiences this increased effective gravity, causing the height to remain constant at 76 cm.

Multiple choice physics pressure in liquids and gases common consequences of the atmospheric pressure atmospheric pressure and its consequences important points about atmospheric pressure

The reading of a barometer containing some air above the mercury column is 73cm while that of a correct one is 76 cm. If the tube of the faulty barometer is pushed down into mercury until volume of air in it is reduced to half, the reading shown by it will be 

  1. 70 CM

  2. 72 CM

  3. 74 CM

  4. 76 CM
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In a faulty barometer with trapped air, the pressure at the mercury surface is P_atm = P_air + P_Hg. Using Boyle's law (P1V1 = P2V2) for the trapped air, where the volume is halved, the pressure of the air doubles. Solving the system of equations leads to the new reading of 70 cm.

Multiple choice physics pressure in liquids and gases common consequences of the atmospheric pressure atmospheric pressure and its consequences important points about atmospheric pressure

To construct a barometer, a tube of length $1 m$ filled completely with mercury and is inverted in a mercury cup. The barometer reading on a particular day is $76\ cm$. Suppose a $1 m$ tube is filled with mercury up to $76\ cm$ and then closed by a cork. It is inverted in a mercury column in the tube over the surface in the cup will be

  1. Zero
  2. $76\ cm$
  3. $> 76\ cm$
  4. $< 76\ cm.$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The tube contains air $($because it is not fully filled$).$ This air pressure against atmosphere pressure$,$ 

therefore$,$ height of column $<76cm$ 
Hence,
option $(D)$ is correct answer.

Multiple choice physics pressure in liquids and gases common consequences of the atmospheric pressure atmospheric pressure and its consequences important points about atmospheric pressure

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

  1. 10 cm

  2. 75 cm

  3. 13.6 cm

  4. 1.36 cm
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The pressure difference between the atmosphere and the lungs supports a column of water. The pressure difference is 10 mm Hg, which is equivalent to 1 cm of Hg. Using P = h_w * d_w * g = h_Hg * d_Hg * g, the height of the water column is 13.6 cm.

Multiple choice physics pressure in liquids and gases common consequences of the atmospheric pressure atmospheric pressure and its consequences important points about atmospheric pressure

Brass scale of a Barometer gives correct reading at  $0 ^ { \circ } \mathrm { C } .$  coefficient of linear expansion of brass is  $18 \times 10 ^ { - 6 } / ^ { - 6 } \mathrm { C } .$  If the barometer reads  $76\mathrm { cm } $ at   $20 ^ { \circ } \mathrm { C } ,$  the correct reading is $\left( \gamma _ { \mathrm { Hg } } = 18 \times 10 ^ { - 5 } / 0 \mathrm { C } \right)$

  1. $76.426 \mathrm { cm }$
  2. $75.7 \mathrm { cm }$
  3. $76.2736 \mathrm { cm }$
  4. $76.264 \mathrm { cm }$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$L _0=75$cm

$\begin{array}{l} a=18\times { 10^{ -6 } }{ /^{ 0 } }C \ \Delta T=20-0={ 27^{ 0 } }C \end{array}$
We know that the formula for the coefficient of linear expansion
$\begin{array}{l} L={ L _{ 0 } }\left( { 1+\alpha \Delta T } \right)  \ L=76\left( { 1+18\times { { 10 }^{ -6 } }\times 20 } \right)  \ =76\left( { 1+0.00036 } \right)  \ =76\times 1.00036 \ =76.2736 \end{array}$
Atmospheric pressure at $20^0C$ is $76.2736$ cm of brass.

Multiple choice physics pressure in liquids and gases common consequences of the atmospheric pressure atmospheric pressure and its consequences important points about atmospheric pressure

State whether true or false:

A simple barometer is compact and portable. 

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

FALSE
A simple barometer is neither portable nor compact. Thus, it cannot be carried from one place to other.
Since the apparatus is made up of glass, so there is also a chance of breaking.

Multiple choice physics pressure in liquids and gases common consequences of the atmospheric pressure atmospheric pressure and its consequences important points about atmospheric pressure

State whether true or false:

The air pressure can support $13.10 m$ vertical column of mercury. 

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$P = \rho gh$, where
$P = $air pressure $= 101325Pa$
$\rho = $density of mercury$ = 13594kg/{m}^{3}$
$\implies h = 0.76m$

It can support 0.76 m vertical column of mercury.
Hence the given statement is false.

Multiple choice physics pressure in liquids and gases common consequences of the atmospheric pressure atmospheric pressure and its consequences important points about atmospheric pressure

Water barometer is possible provided barometer tube is _____$m$ long.

  1. $1$
  2. $3$
  3. $5$
  4. $11$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

If water would be used in barometer, barometer tube should have the huge height of $10.3m$ Mercury is $13.6$ times more dense than water and a column weight of only $760 mm$ of Hg equals the forces generated by atmospheric pressure, so the tube can be much shorter.

Mercury is more dense. Its relative density is $13.534$ times that of water. So, to measure the atmospheric pressure, which is $760 mm$ of mercury you need a barometer ,with mercury, of length slightly more than $0.76 m$, say one meter to cover the special cases of some higher pressure. If you use water, you have to have the length of barometer of length (or height)  $13.534$ times the length of mercury barometer, which may be more than $11 m$ in length. Further mercury, being a metal has the shining quality which highlight its reading clear. Also mercury, having comparatively lower specific heat and good conductor of heat, could come to the same temperature of the atmosphere more quickly.

Multiple choice physics pressure in liquids and gases common consequences of the atmospheric pressure atmospheric pressure and its consequences important points about atmospheric pressure

Water is not used as a barometric liquid because 

  1. it is difficult to have a barometer tube 11 m long.

  2. water vaporises under vacuum conditions.

  3. water sticks to the side of glass tube.

  4. all the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Mercury is more dense. Its relative density is $13.534$ times that of water. So, to measure the atmospheric pressure, which is $760 mm$ of mercury you need a barometer ,with mercury, of length slightly more than $0.76 m$, say one meter to cover the special cases of some higher  pressure. If you use water, you have to have the length of barometer of  length (or height)  $13.534$ times the length of mercury barometer, which  may be more than $11 m$ in length. 


Further mercury, being a metal has the shining quality which highlight its reading clear. Also mercury, having comparatively lower specific heat and good conductor of heat, could come to the same temperature of the atmosphere more quickly.