Tag: physics

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Questions Related to physics

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

If one newton force is applied to unit crossesctional area (in $m^2$)  of any subject then the amount of pressure applied is

  1. one pascal

  2. one atmospheric pressure

  3. one gauge pressure

  4. none of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Pressure is defined as force per unit area applied on a surface.

$P=\dfrac{F}{A}$ 
In SI units, pressure has unit $N/m^2$ which is equivalent to $Pa$(Pascal).

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

The amount by which the pressure measured in a fluid exceeds that of the atmosphere is known as 

  1. atmospheric pressure

  2. gauge pressure

  3. absolute pressure

  4. none of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Gauge Pressure uses a reference to the atmosphere around the sensor. Because the sensing element has a deflection due to a pressure change, a reference point is needed to know exactly what pressure is being measured. Pressure sensors that use gauge pressure—typically seen in PSIG, BARG, and kPaG —have some type of vent. This vent can be built in to the sensor or even through a tube in the electrical connection. The vent is positioned to use atmospheric pressure as a reference point for the sensor to measure the media. One common reason for using gauge pressure is to ensure that with any location throughout the world, the sensor will always reference the location in which it is installed.

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

A bubble is at the bottom of a lake of depth $h$. As the bubble comes to the sea level, its radius increase three times. If atmospheric pressure is equal to $l$ metre of a water column, then $h$ is equal to

  1. $26\ l$

  2. $l$

  3. $25\ l$

  4. $30\ l$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Using Boyle's Law P1V1 = P2V2. Initial pressure P1 = P_atm + rho*g*h. Final pressure P2 = P_atm. Since radius triples, volume increases 27 times. P_atm + rho*g*h = 27 * P_atm. With P_atm = rho*g*l, we get h = 26l.

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

A narrow glass tube, $80$ cm long and opens at both ends, is half immersed in mercury, now the top of the tube is closed and is taken out of mercury A column of mercury $20$ cm long remains in the tube. Find the atmospheric pressure

  1. $20$ cm of air column

  2. $60$ cm of Hg column

  3. $60$ cm of air column

  4. $20$ cm of Hg column
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Using Boyle's Law for the trapped air: P_initial * V_initial = P_final * V_final. Initially, the tube is half-immersed (40 cm air at P_atm). Finally, 20 cm Hg remains, so air column is 60 cm. Solving gives P_atm = 60 cm Hg.

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

A brass scale, correct at $0^\circ C$, registers the height of a mercury barometer at 76.5 cm at $30^\circ c$. What is the actual height of the barometer? [Linear expansivity for brass=$1.9\times10^{-5} K^{-1}$]

  1. 70.88cm

  2. 72.45cm

  3. 71.25cm

  4. 76.46 cm
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The scale expands with temperature. Actual height H = H_observed * (1 + alpha * delta_T). H = 76.5 * (1 + 1.9 * 10^-5 * 30) = 76.5 * (1.00057) = 76.543 cm. The provided answer 76.46 cm suggests a different correction factor or calculation method.

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

A barometer is carried from the $1^{st}$ floor to the $20^{th}$ floor of a building. Why does the reading on the barometer fall?

  1. Air pressure has increased

  2. Gravity has decreased

  3. Temperature has increased

  4. There is less air above the barometer
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Answer is D.

The air pressure decreases as the we go up the atmosphere. Therefore, when a  barometer is carried from the 1st floor to the 20th floor of a building, the air pressure decreases and hence the reading on the barometer falls down.

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

Atmospheric pressure can be measured by which of the following instruments

  1. doctor's thermometer

  2. mercury barometer

  3. speedometer

  4. none of these
Reveal answer Fill a bubble to check yourself
B Correct answer
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.