Tag: devices to measure pressure

Questions Related to devices to measure pressure

Atmospheric pressure can be measured by which of the following instruments

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

  1. doctor's thermometer

  2. mercury barometer

  3. speedometer

  4. none of these

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Correct Option: B
Explanation:

Speedometre is an instrument which is used to measure the speed of a vehicle.

Doctor's thermometre is used to measure the temperature of the body of the patient.
Mercury thermometre is used for measuring the atmospheric pressure.

The pressure energy per unit volume of a liquid is

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

  1. $ \frac {P}{\rho}$

  2. P

  3. P x $\rho$

  4. $ \frac {\rho}{P}$

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Correct Option: B
Explanation:

Pressure energy per unit volume=$=\dfrac{Work done}{Volume}=\dfrac{W}{V}=\dfrac{F.d}{A.d}$

$=\dfrac{F}{A}$
$=P$

'The atmospheric pressure at a place is $76  cm$ of $Hg$? State its value in $bar$.

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

  1. $1.013\times{10}^{5}$ $bar$

  2. $1 bar$

  3. $1.013\times{10}^{-5}$ $bar$

  4. None

Show answer
Correct Option: B
Explanation:

$1atm$ is the standard atmospheric pressure. 
In terms of length of mercury it is $76cm $ of Hg.

In SI units, the atmospheric pressure is $1atm=1.01325\times 10^{5}Nm^{-2}= 1 bar$

Unit for pressure used in weather maps is millibar. 1 millibar is equal to

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

    1. 1000 bar

    2. 100 kPa

    3. 100 Pa

    4. 1 atm

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    Correct Option: C
    Explanation:

    Bar is a unit of pressure.

    $1bar=10^5 Pa$
    Hence dividing by 1000 expresses the milli form of the unit.
    $\implies 1millibar=\dfrac{10^5}{1000}Pa$
    $=100Pa$

    $1\ atm$ of pressure is equal to

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

    1. $1\ Torr$

    2. $\dfrac{1}{760}\ Torr$

    3. $760\ Torr$

    4. $1.013 \times 10^5\ Torr$

    Show answer
    Correct Option: C
    Explanation:

    The pressure due to $760$ mm of mercury is equal to atmospheric pressure. Pressure equivalent to $1$mm of mercury is $1torr$. Hence the atmospheric pressure $1atm=760torr$.

    $1\ Pa$ of pressure is equal to:

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

    1. $7.5 \times 10^{-3}\ Torr$

    2. $7.5 \times 10^{3}\ Torr$

    3. $760\ Torr$

    4. $1\ Torr$

    Show answer
    Correct Option: A
    Explanation:

    Atmospheric pressure $=1atm=760torr=1.01\times 10^3Pa$

    $\implies 1Pa=\dfrac{760}{1.01\times 10^5}torr=7.5\times 10^{-3}torr$

    A measurement referenced to the atmospheric pressure and it varies from the measurement of barometric reading and manometer reading is called as 

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

    1. gauge pressure

    2. absolute pressure

    3. atmospheric pressure

    4. none of the above

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    Correct Option: A
    Explanation:

    Absolute pressure: It uses absolute zero (pressure in vacuum) as its zero point.

    Gauge pressure: It uses atmospheric pressure  as its zero point.
    Therefore, Absolute pressure = Atmospheric pressure + Gauge pressure
    A barometer reads the atmospheric pressure and a manometer reads absolute pressure (when closed from one end), therefore a measurement referenced to the atmospheric pressure varying from barometer reading and manometer is called as gauge pressure.

    A pressure equivalent to 1 mm of mercury is called 

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

    1. 1 torr

    2. 1 bar

    3. 1 pascal

    4. 1 atm

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    Correct Option: A
    Explanation:

    The pressure at the bottom of $760 mm$ of mercury is equal to atmospheric pressure.

    Also, $1atm=760torr$
    Hence, $1torr$ pressure and $1mm$  of mercury are equivalent.

    1 pascal (Pa) is equal to 

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

    1. $1 \times 10^{5} $ bar

    2. $1 \times 10^{3} $ bar

    3. $1 \times 10^{-3} $ bar

    4. $1 \times 10^{-5} $ bar

    Show answer
    Correct Option: D
    Explanation:

    We have,

                   $1 atm=1\times10^{5}Pa$ ,
    and         $1atm=1bar$ ,
    hence,   $1bar=1\times10^{5}Pa$ 
    or            $1Pa=1\times10^{-5}bar$

    $1\ Torr$ of pressure is equal to:

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

    1. $133\ Pa$

    2. $13\ Pa$

    3. $1\ Pa$

    4. none of these

    Show answer
    Correct Option: A
    Explanation:

    Atmospheric pressure $=1atm=1.01\times 10^5Pa=760torr$

    $\implies 1torr=\dfrac{1.01\times 10^5}{760}Pa$$=133Pa$