Tag: physics

Questions Related to physics

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

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

  1. $76\ cm$

  2. $> 76\ cm$

  3. $< 76\ cm$

  4. Zero

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Correct Option: A

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 

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

  1. 70 CM

  2. 72 CM

  3. 74 CM

  4. 76 CM

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Correct Option: A

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

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

  1. Zero

  2. $76\ cm$

  3. $> 76\ cm$

  4. $< 76\ cm.$

Show answer
Correct Option: D
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.

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

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

  1. 10 cm

  2. 75 cm

  3. 13.6 cm

  4. 1.36 cm

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Correct Option: C

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 $\left( \gamma _ { \mathrm { Hg } } = 18 \times 10 ^ { - 5 } / 0 \mathrm { C } \right)$

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

  1. $76.426 \mathrm { cm }$

  2. $75.7 \mathrm { cm }$

  3. $76.2736 \mathrm { cm }$

  4. $76.264 \mathrm { cm }$

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Correct Option: C
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.

A barometer kept in a stationary elevator reads $76 \mathrm { cm } ,$ If the elevator starts accelerating up the reading willbe 

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

  1. Zero

  2. equal to 76$\mathrm { cm }$

  3. more than 76$\mathrm { cm }$

  4. less than 76$\mathrm { cm }$

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Correct Option: D

State whether true or false:

A simple barometer is compact and portable. 

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

  1. True

  2. False

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Correct Option: B
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.

State whether true or false:

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

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

  1. True

  2. False

Show answer
Correct Option: B
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.

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

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

  1. $1$

  2. $3$

  3. $5$

  4. $11$

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Correct Option: D
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.

Water is not used as a barometric liquid because 

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

  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

Show answer
Correct Option: D
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.