Chapter 7, Problem 7.39P

Interpretation Introduction

(a)

Interpretation:

In the pressure gauge, which is used for scuba diving, the indicated pressure needs to be determined.

Concept Introduction:

Pressure is defined as the force applied per unit surface area. There are many techniques used for measurement. In the case of fluids, it is the force applied by the particles of the liquid on the walls of the container.

Answer to Problem 7.39P

The reading on the pressure gauge shows 2600 psi.

Explanation of Solution

The pressure gauge as shown in the diagram has scale reading from 0 to 4000. Each unit is 500 psi and there are 4 subdivisions between each unit. This means that from 0 -500, each subunit is to be considered as 100 psi.

Now taking a closer look at the needle pointer, it is seen that the needle is one unit after 2500. This means that it is read as 2500+100=2600.

Thus, the needle indicating the pressure on the pressure gauge is 2600 psi.

  

Interpretation Introduction

(b)

Interpretation:

The measured pressure in psi needs to be converted into mm Hg.

Concept Introduction:

The standard atmospheric pressure is equivalent to 760mm Hg. This unit is roughly equal to the atmospheric pressure.

  $1\text{ atm}=\text{760 mm Hg}$

Also, the relation between the pressure in psi and atmospheric pressure is as follows:

  $1\text{ atm}=14.7\text{ psi}$

Answer to Problem 7.39P

The value after converting pressure in psi to mmHg is $\text{1}\text{.3}\times {\text{10}}^{\text{5}}\text{ mmHg}$.

Explanation of Solution

The conversion of psi to mmHg is as follows:

1 psi = 51.71484 mmHg

Hence, 2600 psi is converted as

  $\begin{array}{l}\text{=2600 psi }\left(\frac{\text{ 51}\text{.71484 mm Hg}}{1\text{ psi}}\right)\\ \text{=134,458}\text{.48 mm Hg}\\ \text{=1}\text{.3}\times {\text{10}}^5\text{ mmHg}\end{array}$

Therefore, the pressure value is $\text{1}\text{.3}\times {\text{10}}^{\text{5}}\text{ mmHg}$.