Barometer And Manometer - Practice Questions & MCQ

Barometer-

Mercury Barometer was invented by Torricelli and it is a device used for measuring pressure.

Below is a figure showing the  Mercury Barometer device

From the figure we can say that

At Point C only atmospheric pressure is there.

So $P_C=P_0$
Ans since $B$ and $C$ are at the same horizontal level
So $P_C=P_B=P_A+\rho g h=0+\rho g h=\rho g h=P_0=$ Atmospheric pressure
For mercury barometer $\mathrm{h}=76 \mathrm{~cm}$ and
And using $\rho=13.6 * 10^3 \mathrm{~kg} / \mathrm{m}^3$
We get $P_0=1.013 * 10^5 \mathrm{~N} / \mathrm{m}^2=1 \mathrm{~atm}=76 \mathrm{~cm}$ of Hg

Manometer-

Manometers are the devices used for measuring gauge pressure of fluids.

Simple Manometer-

The figure of Simple Manometer is given below

And from the figure we can say that

The gauge pressure at point A in the vessel is 

$P_A=\rho g h$

Where =density of the liquid

U-tube Manometer-

Figure of U-tube manometer is given below

And from the figure we can say that

$
P_A=P_B
$

And The gauge pressure at point A is given by

$
P_A=\rho g h
$
 

Where

=density of the liquid