An application of Bernoulli's equation for fluid flow is found in

$Assertion :$ The velocity of flow of a liquid is smaller when pressure is larger and vice-versa.
$Reason :$ According to Bernoulli's theorem,for the stream line flow of an ideal liquid,the total energy per unit mass remains constant.

Water (of density $\varrho$) flows steadily through a horizontal pipe of variable cross-section. If the pressure of water is $P$ at a point where the flow speed is $V$,then the pressure at another point where the flow speed becomes $3V$ is:

Water is flowing in a conical tube as shown in the figure. The velocity of water at area $A_2$ is $60 \,cm/s$. The values of $A_1$ and $A_2$ are $10 \,cm^2$ and $5 \,cm^2$ respectively. The pressure difference between the two cross-sections is: (in $\,N/m^2$)

What is a venturi-meter? Explain its construction and working.