Question

Action of paint gun is based on:
A. Bernoulli’s principle
B. Boyle’s law
C. Faraday’s law
D. Archimedes principle

Answer 1

Bernoulli’s principle gives the relation between pressure acting at a point on the surface of the liquid and the velocity of its particle. The principle states that the total energy of a small amount of an incompressible liquid flowing through a stream from one point to another remains constant throughout the displacement.

Complete step by step answer:
Look into the figure of the spray gun shown below.

We know that a spray gun is a kind of atomizer, i.e. an instrument used to spray liquids.
From the figure, we can see that in a spray gun apparatus we have a rubber bulb (represented by ‘B’), a narrow glass tube (represented by ‘T’) and a narrow aperture at the end (represented by ‘O’).
As we can see, the tube is inserted into the liquid. Now, when we squeeze the rubber bulb, the air flows through the tube and comes out through the narrow aperture at the end.
Since the aperture ‘O’ is narrow, the velocity of the air will increase when the air escapes out.
Hence, the pressure near ‘O’ gets reduced.
Therefore a pressure difference is caused there.
Due to the difference in pressure the liquid in the bottle rises through the vertical tube. But the stream of air coming through the tube due to the squeezing of the bulb blows the liquid into a fine spray.
Therefore, we can say that the action of a spray gun is based on Bernoulli’s principle.

Hence the correct answer is option A.

Note:
Bernoulli’s principle relation is a relation between pressure, kinetic energy and gravitational potential energy of a fluid in a stream line flow.
It is given as,
$P+\dfrac{1}{2}\rho {{V}^{2}}+\rho gh=\text{constant}$
Some other applications of Bernoulli’s principle are,
Venturi meter: It is an instrument used for measuring the rate of flow of liquids through pipes. This works on the principle of Bernoulli’s theorem.
The shape of the wings of the airplane is in such a way that the air passes at a higher speed over the upper surface of the wing than on the lower surface. The difference in the speed of the air is determined using Bernoulli’s equation.