**UPDATED* Chapter 06: Physical Principles of Respiratory Care

What is the physical process whereby the gaseous form of a substance is changed back into its liquid state? a. Condensation b. Sublimation c. Vaporization d. Radiation

ANS: A During condensation, a gas turns back into a liquid.

For every liquid, there is a temperature above which the kinetic activity of its molecules is so great that the attractive forces cannot keep them in a liquid state. This temperature is called the a. critical temperature. b. melting point. c. flash temperature. d. triple point.

ANS: A When a liquid is heated to its critical temperature, it converts to a gas. This temperature is called the critical temperature.

By which of the following means can the internal energy of a substance be increased? 1. Cooling the substance 2. Performing work on the substance 3. Heating the substance a. 2 and 3 only b. 1 and 2 only c. 2 only d. 3 only

ANS: A You can increase the internal energy of an object by heating it or by performing work on it

What occurs during the evaporation of water? a. The adjacent air is warmed. b. The adjacent air is cooled. c. The water temperature rises. d. Heat is given up to the air.

ANS: B As the surrounding air loses heat energy, it cools. This is the principle of evaporation cooling.

Which of the following is a good clinical example of using the principle of convection to transfer heat? a. Humidifiers with immersion heaters b. Heated, enclosed infant incubators c. Wire-heated pneumotachometers d. Heated ventilator exhalation valves

ANS: B This is the principle behind forced-air heating in houses and convection heating in infant incubators.

Assuming a constant flow, what will happen to a fluid if the cross-sectional area of the tube in which its flows decrease? a. Its velocity will increase. b. Its velocity will decrease. c. Its density will decrease. d. Its viscosity will decrease.

ANS: B Throughout the tube, the fluid flows at a constant rate of 5 L/min. At point A, with a cross-sectional area of 5.08 cm2 , the velocity of the fluid is 16.4 cm/sec. At point B, the cross-sectional area of the tube decreases to 2.54 cm2 , half its prior value. At this point, the velocity of the fluid doubles to 32.8 cm/sec

What is the pattern of flow in which a fluid moves in discrete cylindrical streamlines? a. Transitional b. Turbulent c. Laminar d. Tracheal

ANS: C During laminar flow, a fluid moves in discrete cylindrical layers or streamlines.

The resistance to flow of a fluid through a tube can be computed according to which of the following formulas? a. Resistance = flow viscosity b. Resistance = flow ÷ pressure c. Resistance = pressure ÷ flow d. Resistance = flow pressure

ANS: C For any given tube length, flow resistance equals the difference in pressure between the two points along the tube divided by the actual flow. This is expressed as a formula: R = (P1 ?- P2) ÷ V

What is the density of a mixture of 40% oxygen (O2) and 60% helium at STPD? a. 0.34 g/L b. 0.55 g/L c. 0.68 g/L d. 1.25 g/L

ANS: C For the density of a gas mixture to be calculated, the percentage or fraction of each gas in the mixture must be known. For example, to calculate the density of air at STPD, the following equation is used: dwair = (FN2 gmw N2) + (FO2 gmw O2) ÷ 22.4 Ldwair = (0.79 28) + (0.21 32) ÷ 22.4 L dwair = 1.29 g/L

If a given mass of a gas is maintained at a constant temperature, what will decreasing its pressure do? a. Decrease its volume. b. Increase its mass. c. Increase its volume. d. Decrease its mass.

ANS: C If a gas-filled container could be enlarged, the gas would expand to occupy the new volume

Which of the following will occur when a gas undergoes expansion? 1. The pressure of the gas increases. 2. Molecular collisions decrease. 3. The gas temperature increases. a. 1 and 2 only b. 2 and 3 only c. 2 only d. 3 only

ANS: C If a gas-filled container could be enlarged, the gas would expand to occupy the new volume

Which of the following conditions tend to cause laminar flow to become turbulent (producing a high Reynold's number)? 1. High linear gas velocity 2. High gas density 3. Low gas viscosity 4. Smaller tube diameter a. 2, 3, and 4 only b. 2 and 3 only c. 1, 2, and 3 only d. 1 and 4 only

ANS: C In a smooth-bore tube, the laminar flow becomes turbulent when NR exceeds 2000 (the number is dimensionless). According to the previous formula, conditions favoring turbulent flow include increased fluid velocity, increased fluid density, increased tube radius, or decreased fluid viscosity. In the presence of irregular tube walls, turbulent flow can occur when NR is less than 2000

What is the term for the temperature at which the water vapor in a gas begins to condense back into a liquid? a. Triple point b. Critical pressure c. Dew point d. Boiling point

ANS: C The temperature at which condensation begins is called the dew point.

Which of the following would be the worst heat conductor? a. Water b. Glass c. Air d. Copper

ANS: C With fewer molecular collisions than in solids and liquids, gases exhibit low thermal conductivity.

What occurs when the temperature of a saturated gas drops down to its dew point? a. Excess water vapor will condense as visible droplets. b. The temperature of the surrounding air decreases. c. Any liquid water present will quickly evaporate. d. The relative humidity of the gas begins to decrease.

ANS: A Cooling a saturated gas below its dew point causes increasingly more water vapor to condense into liquid water droplets.

Solids maintain their shape because their atoms are kept in place by strong mutual attractive forces, called a. van der Waals forces. b. thermodynamic equilibrium. c. buoyancy. d. fluidics.

ANS: A Solids maintain their shape because their atoms are kept in place by strong mutual attractive forces, called van der Waals forces.

The ratio of the density of one fluid when compared with the density of another reference substance, which is typically water, describes the fluid's a. specific gravity. b. specific weight. c. atomic mass. d. atomic volume.

ANS: A The term specific gravity refers to the ratio of the density of one fluid when compared with the density of another reference substance which is typically water.

What is the change in state of a substance from liquid to gaseous form occurring below its boiling point? a. Evaporation b. Sublimation c. Boiling d. Vaporization

ANS: A A liquid can also change into a gas at temperatures lower than its boiling point through a process called evaporation.

Which of the following medical gases can be maintained in liquid form at room temperature? 1. Nitrous oxide 2. Carbon dioxide 3. O2 4. Helium a. 1 and 2 only b. 2, 3, and 4 only c. 2 and 3 only d. 2 and 4 only

ANS: A Both CO2 and N2O have critical temperatures above normal room temperature (Table 6-5).

What is the phenomenon whereby a liquid in a small tube tends to move upward against the force of gravity? a. Capillary action b. Shear stress c. Surface tension d. Buoyancy

ANS: A Capillary action is a phenomenon in which a liquid in a small tube moves upward against gravity

Which of the following is/are good clinical example(s) of the principle of capillary action? 1. Capillary stick blood samples 2. Absorbent humidifier wicks 3. Certain surgical dressings a. 1, 2, and 3 b. 1 and 2 only c. 2 and 3 only d. 2 only

ANS: A Capillary action is the basis for blood samples obtained by use of a capillary tube. The absorbent wicks used in some gas humidifiers are also an application of this principle, as are certain types of surgical dressings.

A gas at 50 C with a relative humidity of 100% is cooled to 37 C. Which of the following will occur? 1. Condensation on surfaces 2. Visible droplet formation 3. Warming of the adjacent air a. 1, 2, and 3 b. 1 and 2 only c. 1 and 3 only d. 2 and 3 only

ANS: A Condensed moisture deposits on any available surface, such as on the walls of a container or delivery tubing, or even on particles suspended in the gas. Condensation returns heat to and warms the surrounding environment, whereas vaporization of water cools the adjacent air.

In what processes of gas compression or expansion does the temperature remain constant? a. Isothermal b. Adiabatic c. Hypothermal d. Neutral kinetic

ANS: A During isothermal conditions, the temperature of an ideal gas should not change with either expansion or contraction.

What is the water vapor pressure of saturated gas at normal body temperature (37 C)? a. 47.0 mm Hg b. 43.8 mm Hg c. 37.0 mm Hg d. 98.6 mm Hg

ANS: A For example, air that is fully saturated with water vapor at 37 C and 760 mm Hg has a water vapor pressure of 47 mm Hg and an absolute humidity of 43.8 mg/L.

What is the primary means by which heat transfer occurs in fluids? a. Convection b. Radiation c. Conduction d. Evaporation

ANS: A Heat transfer in both liquids and gases occurs mainly by convection.

What is the motion referred to when solid molecules travel until they collide? a. Jiggle b. Jingle c. Surface tension d. Boiling point

ANS: A Solids have a fixed volume and shape. The molecules comprising the solid have the shortest distance to travel until they collide with one another. This motion has been referred to as a "jiggle."

What is the term for the ratio of the amount of water vapor in a volume of gas compared to the amount of the water in gas saturated at a normal body temperature of 37 C? a. Percent body humidity (BH) b. Relative humidity (RH) c. Absolute humidity d. Water vapor pressure

ANS: A The %BH of a gas is the ratio of its actual water vapor content to the water vapor capacity in saturated gas at body temperature (37 C). Thus, %BH is the same as RH, except that the capacity (or denominator) is fixed at 43.8 mg/L

The American National Standards Institute has set a water vapor content level of 30 mg/L as the minimum absolute humidity required for patients whose upper airways have been bypassed. This equals what body humidity (BH)? a. 68% b. 47% c. 75% d. 100%

ANS: A The %BH of a gas is the ratio of its actual water vapor content to the water vapor capacity in saturated gas at body temperature (37 C). Thus, %BH is the same as relative humidity, except that the capacity (or denominator) is fixed at 43.8 mg/L

At what temperature do all kinetic activities of matter cease? a. 0 K b. 0 degrees C c. 32 degrees C d. 0 degrees F

ANS: A The SI (Systeme Internationale) units for temperature are degrees Kelvin, with a zero point equal to absolute zero (0 K).

For which of the following purposes might a Venturi tube be used? 1. To restore fluid pressure distal to a restricted orifice 2. To help keep entrainment ratios constant with varying flows 3. To make possible entrainment of large volumes of gas a. 1, 2, and 3 b. 2 and 3 only c. 1 and 2 only d. 1 and 3 only

ANS: A The Venturi tube, as compared with a simple air injector, provides greater entrainment. Moreover, this design helps keep the percentage of entrained fluid constant, even when the total flow varies. A Venturi tube widens just after its jet or nozzle. As long as the angle of dilation is less than 15 degrees, this widening helps restore fluid pressure back toward project levels. However, the Venturi tube has one major drawback—any buildup of pressure downstream from the entrainment port decreases fluid entrainment.

What is the temperature at which the vapor pressure of a liquid equals the pressure exerted on the liquid by the surrounding atmosphere? a. Boiling point b. Dew point c. Triple point d. Melting point

ANS: A The boiling point of a liquid is the temperature at which its vapor pressure equals atmospheric pressure.

Which of the following occurs when the temperature of a gas rises? 1. The kinetic activity of the gas increases. 2. The rate of molecular collisions increases. 3. The pressure exerted by the gas rises. a. 1, 2, and 3 b. 1 and 2 only c. 2 and 3 only d. 3 only

ANS: A The velocity of gas molecules is directly proportional to temperature. As gas is warmed, its kinetic activity increases, its molecular collisions increase, and its pressure rises.

Under conditions of turbulent flow, what is the driving pressure? a. Proportional to the square of the flow b. Inversely proportional to the flow c. Linearly proportional to the flow d. Inversely proportional to the density

ANS: A This changeover from laminar to turbulent flow depends on several factors, including fluid density (d), viscosity (h), linear velocity (v), and tube radius (r). In combination, these factors determine Reynold's number (NR):NR = v d 2r/h

Does a patient have a recorded body temperature of 106 F. What is this temperature in degrees Celsius? a. 41 degrees C b. 98 degrees C c. 39 degrees C d. 22 degrees C

ANS: A To convert degrees Fahrenheit to degrees Celsius, use the following formula: C = 5/9 ( F - 32).

What is the term for the ratio of the actual water vapor present in a gas compared with the capacity of that gas to hold the vapor at a given temperature? a. Relative humidity b. Absolute humidity c. Water vapor pressure d. Percent body humidity

ANS: A When a gas is not fully saturated, its water vapor content can be expressed in relative terms using a measure called relative humidity

According to Avogadro's law, under standard conditions of temperature and pressure (0 C and 760 mm Hg), 1 mol of any gas occupies which of the following? a. 1.34 L b. 22.40 L c. 7.48 L d. 28.30 L

ANS: B At standard temperature and pressure, dry (STPD), the ideal molar volume of any gas is 22.4 L

The peak pressure on a ventilator reads 40 cm H2O. What is the equivalent pressure in mm Hg? a. 37.0 mm Hg b. 29.6 mm Hg c. 68.3 mm Hg d. 4.9 mm Hg

ANS: B Because of mercury's high density (13.6 g/cm3), it assumes a height that is easy to read for most pressures in the clinical range. Water columns can also be used to measure pressure (in cm H2O), but only at low pressures. Because water is 13.6 times less dense than mercury, 1 atm.

From a bedside capnograph (CO2 measuring device), you obtain a "dry" gas reading of 5.3% CO2 in a patient's exhaled gas. Given a barometric pressure of 765 mm Hg, what is the partial pressure of CO2 in this patient's exhaled gas? a. 347 mm Hg b. 41 mm Hg c. 164 mm Hg d. 35 mm Hg

ANS: B Dalton's law describes the relationship among the partial pressure and the total pressure in a gas mixture. According to this law, the total pressure of a mixture of gases must equal the sum of the partial pressures of all component gases. Moreover, the principle states that the partial pressure of a component gas must be proportional to its percentage in the mixture.

At 37 C and 760 mm Hg pressure, 0.023 ml of O2 can be dissolved in 1 ml of plasma, whereas at the same temperature and pressure, 0.510 ml of CO2 will dissolve in 1 ml of plasma. What explains this difference? a. CO2 diffuses more rapidly than O2. b. CO2 is more soluble in plasma than O2. c. CO2 has a greater molecular weight than O2. d. O2 has less affinity for plasma than CO2.

ANS: B For example, the solubility coefficient of O2 in plasma, at 37 C and 760 torr pressure, is 0.023 ml/ml. Under the same conditions, 0.510 ml of CO2 can dissolve in 1 ml of plasma.

Which of the following statements correctly describes gases? 1. Gases exhibit the phenomenon of flow. 2. Molecular forces of attraction are minimal. 3. Gases are challenging to compress. 4. Gases expand to fill their container. a. 1 and 2 only b. 1, 2, and 4 only c. 2, 3, and 4 only d. 3 and 4 only

ANS: B In a gas, attractive molecular forces are fragile. Thus, gas molecules, which lack restriction to their movement, exhibit rapid, random motion with frequent collisions. Gases have no inherent boundaries and are easily compressed and expanded. Moreover, like liquids, gases can flow.

Which of the following statements are true about viscosity? 1. The greater the viscosity, the greater the opposition to flow. 2. Viscosity is most important under conditions of turbulent flow. 3. The stronger the cohesive forces, the greater the viscosity. 4. Fluid viscosity is equivalent to friction between solids. a. 2 and 4 only b. 1, 3, and 4 only c. 1 and 3 only d. 2, 3, and 4 only

ANS: B Laminar flow consists of concentric layers of fluid flowing parallel to the tube wall at velocities that increase toward the center.

Which of the following design components of an air injector would result in entraining the greatest amount of air? 1. Small orifice jet 2. Large entrainment ports 3. Low-velocity gas flow a. 1, 2, and 3 b. 1 and 2 only c. 1 and 3 only d. 3 only

ANS: B The amount of air entrained depends on both the diameter of the jet orifice and the size of the air-entrainment ports. For a fixed jet size, the larger the entrainment ports, the greater the volume of air entrained and the higher the total flow. The entrained volume can still be altered, with fixed entrainment ports, by changing the jet diameter. Large jet results in a lower gas velocity and less entrainment, whereas a small jet boosts velocity, entrained volume, and total flow

According to Pascal's principle, the pressure exerted by a liquid in a container depends on which of the following? 1. Depth of the liquid 2. Density of the liquid 3. Shape of the container a. 3 only b. 1 and 2 c. 2 only d. 1 and 3

ANS: B The pressure exerted by a liquid depends on both its height (depth) and weight density (weight per unit volume), which is shown in equation form: PL = h dw.

Does a near-drowning patient have a recorded body temperature of 30 C. What is the equivalent temperature in degrees Fahrenheit? a. -4 F b. 86 F c. 32 F d. 77 F

ANS: B To convert degrees Celsius to degrees Fahrenheit, simply reverse the formula given in question 4: F = (9/5 C) + 32.

Which of the following represents a direct measure of the kinetic activity of water vapor molecules? a. Absolute humidity b. Water vapor pressure c. Percent body humidity d. Relative humidity

ANS: B Water vapor pressure represents the kinetic activity of water molecules in air.

When the water vapor content of a volume of gas equals its capacity, what is the relative humidity (RH) of this gas? a. 80% b. 100% c. 40% d. 60%

ANS: B When the water vapor content of a volume of gas equals its capacity, the RH is 100%. When the RH is 100%, a gas is fully saturated with water vapor.

A combination of neutral atoms, free electrons, and atomic nuclei describes a. potential energy. b. kinetic energy. c. plasma. d. compressed gases.

ANS: C Plasma has been referred to as the fourth state of matter and is a combination of neutral atoms, free electrons, and atomic nuclei. Plasmas can react to electromagnetic forces and flow freely like a liquid or a gas.

You obtain a mercury barometric reading of 760 mm Hg at 17 C. Using the following factor table, compute the corrected pressure. C 740 750 760 17 2.17 2.20 2.23 18 2.29 2.32 2.35 19 2.38 2.41 2.44 a. 223.0 mm Hg b. 747.7 mm Hg c. 757.8 mm Hg d. 762.3 mm Hg

ANS: C The U.S. Weather Bureau provides temperature correction factors for barometric readings.

What is the term for the actual content or weight of water present in a given volume of air? a. Percent body humidity b. Water vapor pressure c. Absolute humidity d. Relative humidity

ANS: C Absolute humidity can be measured by weighing the water vapor extracted from air using a drying agent

What is the equilibrium condition in which a gas holds all the water vapor molecules that it can? a. Evaporation b. Stabilization c. Saturation d. Body humidity

ANS: C At this point, the air over the water is saturated with water vapor. However, vaporization does not stop once saturation occurs.

Which of the following are true about boiling? 1. Boiling a liquid requires more energy than does evaporating it. 2. A liquid's boiling point varies with the atmospheric pressure. 3. The greater the ambient pressure, the lower is the boiling point. a. 2 and 3 only b. 1 and 3 only c. 1 and 2 only d. 1, 2, and 3

ANS: C Because the weight of the atmosphere retards the escape of vapor molecules, the greater the ambient pressure, the greater is the boiling point.

What are the forms of vaporization? 1. Boiling 2. Freezing 3. Evaporation 4. Sublimation a. 3 only b. 1 and 2 only c. 1 and 3 only d. 1, 2, and 4 only

ANS: C Both boiling and evaporation are forms of vaporization.

Archimedes' principle is applied clinically in which of the following devices? a. Nebulizer b. Capillary tube c. Hydrometer d. Humidifier

ANS: C Clinically, Archimedes' principle is used to measure the specific gravity of certain liquids. A hydrometer is used to measure the specific gravity of certain liquids.

During some pulmonary function tests, saturated gas exhaled from a patient's lungs is gathered at room temperature. Which of the following correction-factor tables would you use to determine what volume this gas occupied in the patient's lungs? a. Standard temperature, standard pressure, dry (STPD) to body temperature, ambient pressure, saturated (BTPS) b. BTPS to STPD c. Ambient temperature, ambient pressure, saturated (ATPS) to BTPS d. ATPS to STPD

ANS: C Correction from ATPS to standard temperature and pressure (0 C and 760 torr), dry (STPD).

What is the physical process whereby atoms or molecules tend to move from an area of higher concentration or pressure to an area of lower concentration or pressure? a. Sublimation b. Melting c. Diffusion d. Capillary action

ANS: C Diffusion is the process whereby molecules move from areas of high concentration to areas of lower concentration.

What is the most common application of Bernoulli's principle in respiratory care equipment? a. Fluidic ventilator b. Pneumotachygraph c. Air injector d. U-tube manometer

ANS: C In respiratory care, the most common application of fluid entrainment is the air injector.

Which of the following would help to decrease a patient's loss of body heat? 1. Increase the temperature of the room. 2. Increase the exposed skin surface area. 3. Move the patient away from cold windows. a. 1 and 2 only b. 2 and 3 only c. 1 and 3 only d. 3 only

ANS: C In simple terms, for an object with a given emissivity, the larger the surface area (relative to mass) and the lower the surrounding temperature, the greater is the radiant heat loss per unit time.

Which of the following is a false statement about O2? a. No pressure can keep it in a liquid state above -118.8 C. b. Below its boiling point, it remains liquid at ambient pressure. c. Its critical temperature is above normal room temperature. d. It cannot be turned into a liquid at room temperature.

ANS: C Liquid O2 is produced by separating it from a liquefied air mixture at a temperature below its boiling point or critical temperature (-183 C or -297 F). After it is separated from air, the O2 must be maintained as a liquid by being stored in insulated containers below its boiling point. As long as the temperature does not exceed -183 C, the O2 will remain liquid at atmospheric pressure. If higher temperatures are needed, higher pressures must be used. If at any time the liquid O2 exceeds its critical temperature of -118.8 C, it will convert immediately to a gas.

According to Poiseuille's law, the pressure needed to drive a fluid through a tube will increase under which of the following conditions? 1. Increased fluid viscosity 2. Decreased tube length 3. Decreased rate of flow 4. Decreased tube radius a. 1 and 2 only b. 2, 3, and 4 only c. 1 and 4 only d. 1, 3, and 4 only

ANS: C The difference in pressure required to produce a given flow, under conditions of laminar flow through a smooth tube of fixed size, is defined by Poiseuille's law:P = 8nl/r4, where P is the driving pressure gradient, n is the viscosity of the fluid, l is the tube length is the fluid flow, r is the tube radius, and 8 is a constant.

Which of the following occurs (s) when water vapor is added to dry gas at constant pressure? 1. The volume occupied by the gas mixture decreases. 2. The relative humidity of the mixture increases. 3. The partial pressure of the original gas is reduced. a. 1 and 2 only b. 1 and 3 only c. 1, 2 and 3 d. 3 only

ANS: C The dry volume of a gas at a constant pressure and temperature is always smaller than its saturated volume. The opposite is also true. Correcting from the dry state to the saturated state always yields a larger gas volume. The pressure exerted by water vapor is independent of the other gases with which it mixes, depending only on the temperature and RH. Therefore, the addition of water vapor to a gas mixture always lowers the partial pressures of the other gases present.

Both a compressed gas cylinder and its regulator are at room temperature with all valves in the off position. After the cylinder is opened and gas begins flowing, you note that the regulator is extremely cold to touch. Which of the following principles best explains this observation? a. Adiabatic compression b. Gay-Lussac's law c. Joule-Thompson effect d. Venturi principle

ANS: C The rapid expansion of real gases causes substantial cooling. This phenomenon of expansion cooling is called the Joule-Thompson effect. Adiabatic compression can also occur in gas delivery systems where rapid compression occurs within a fixed container. The rise in temperature caused by this rapid compression can ignite any combustible material in the system. It is for this reason that RTs must take care to clear any combustible matter from high-pressure gas delivery systems before pressurization.

What is the internal force that opposes the flow of fluids (equivalent to friction between solid substances)? a. Conductivity b. Kinetic energy c. Viscosity d. Density

ANS: C Viscosity is the force opposing a fluid's flow.

Which of the following equations can be used to calculate the pressure exerted by a liquid? a. Liquid pressure = liquid depth ÷ liquid density b. Liquid pressure = liquid depth surface area c. Liquid pressure = liquid density liquid viscosity d. Liquid pressure = liquid density liquid depth

ANS: D The pressure exerted by a liquid depends on both its height (depth) and weight density (weight per unit volume), which is shown in equation form: PL = h dw.

One atmosphere (1 atm) of pressure is equivalent to which of the following? 1. 29.9 in Hg 2. 14.7 lb/in2 3. 1034.0 g/cm2 4. 76 mm Hg a. 1, 2, and 3 b. 2 and 4 c. 1 and 3 d. 1, 2, and 3 only

ANS: D At sea level, the average atmospheric pressure will support a column of mercury 76 cm (760 mm) or 29.9 in height. If we also know that mercury has a density of 13.6 g/cm3(0.491 lb/in3), then the average atmospheric pressure (PB) is calculated as follows: cgs units: PB = 76 cm 13.6 g/cm3 = 1034 g/cm2fps units: PB = 29.9 in 0.491 lb/in3 = 14.7 lb/in2

With all else equal, under which of the following conditions would the drop in pressure occurring while a fluid flows through a tube be greatest? a Tube Diameter Fluid Viscosity A Small Low B Large Low C Large High D Small High a. A; Small; Low b. B; Large; Low c. C; Large; High d. D; Small; High

ANS: D Available energy decreases because frictional forces oppose fluid flow. Frictional resistance to flow exists both within the fluid itself (viscosity) and between the fluid and the tube wall. In general, the greater the viscosity of the fluid and the smaller the cross-sectional area of the tube, the greater is the drop in pressure along the tube.

According to Avogadro's law, which of the following is/are TRUE? 1. One gram of any substance contains the same number of particles. 2. Equal volumes of gases at standard temperature, standard pressure, and dry (STPD) have the same number of molecules. 3. Equal numbers of gas molecules at STPD occupy the same volume. a. 1 and 2 only b. 1, 2, and 3 c. 2 and 3 only d. 1 only

ANS: D Avogadro's law states that the 1-g atomic weight of any substance contains exactly the same number of atoms, molecules, or ions.

What term is used for the transfer of heat by the direct interaction of atoms or molecules in a hot area with atoms or molecules in a cooler area? a. Radiation b. Convection c. Condensation d. Conduction

ANS: D Conduction is the transfer of heat by direct contact between hot and cold molecules

In the lung's alveoli, there are four gases mixed together: O2, carbon dioxide, nitrogen, and water vapor. At a normal barometric pressure of 760 mm Hg, alveolar O2 exerts a partial pressure of 100 mm Hg, CO2 40 mm Hg, and water vapor 47 mm Hg. What is the alveolar partial pressure of nitrogen? a. 187 mm Hg b. 713 mm Hg c. 660 mm Hg d. 573 mm Hg

ANS: D Dalton's law describes the relationship among the partial pressure and the total pressure in a gas mixture. According to this law, the total pressure of a mixture of gases must equal the sumof the partial pressures of all component gases. Moreover, the principle states that the partial pressure of a component gas must be proportional to its percentage in the mixture.

What is the absolute humidity (water vapor content) of saturated gas at normal body temperature (37 C)? a. 47.0 mg/L b. 37.0 mg/L c. 98.6 mg/L d. 43.8 mg/L

ANS: D For example, air that is fully saturated with water vapor at 37 C and 760 mm Hg has a water vapor pressure of 47 mm Hg and an absolute humidity of 43.8 mg/L.

Which of the following factors determine how much of a given gas can dissolve in a liquid? 1. Solubility coefficient of the gas 2. Temperature of the liquid 3. Gas pressure above the liquid a. 2 and 3 only b. 1 and 2 only c. 1 and 3 only d. 1, 2, and 3

ANS: D Henry's law predicts how much of a given gas will dissolve in a liquid. According to this principle, at a given temperature, the volume of a gas that dissolves in a liquid is equal to its solubility coefficient times its partial pressure.

Respiratory therapists must ensure that any oil or dust is cleared from high-pressure medical-gas delivery systems before pressurization. Why is this action needed? a. Inhaled dust particles can cause pneumoconiosis. b. The oil or dust can cause a leak in the system. c. Oil or dust does not easily mix with medical gases. d. Adiabatic compression could ignite the oil or dust.

ANS: D In an adiabatic process, the container is insulated, resulting in no heat transfer into or out from the system. If the volume increases, the internal energy decreases to perform the work and thus the temperature decreases. If the volume is increased the internal energy is also increased, resulting in a higher temperature

What temperature is necessary to liquefy O2 at 1 atm pressure? a. -118.8 C b. -181.1 F c. -463.3 F d. -183.0 C

ANS: D Liquid O2 is produced by separating it from a liquefied air mixture at a temperature below its boiling point (-183 C or -297 F). After it is separated from air, the O2 must be maintained as a liquid by being stored in insulated containers below its boiling point. As long as the temperature does not exceed -183 C, the O2 will remain liquid at atmospheric pressure. If higher temperatures are needed, higher pressures must be used. If at any time the liquid O2 exceeds its critical temperature of -118.8 C, it will convert immediately to a gas

Which of the following are true of liquids? 1. They are easy to compress. 2. They exert pressure. 3. They exert buoyant force. 4. They conform to their containers. a. 2 and 4 only b. 1, 2, and 3 only c. 1 and 3 only d. 2, 3, and 4 only

ANS: D Liquids exhibit flow and assume the shape of their container. Liquids also exert pressure, which varies with depth and density. Variations in liquid pressure within a container produce an upward supporting force, called buoyancy.

The peak pressure on a ventilator reads 30 cm H2O. What is the equivalent pressure in kilopascals (kPa)? a. 37.0 kPa b. 68.0 kPa c. 4.9 kPa d. 2.9 kPa

ANS: D One kPa equals approximately 10.2 cm H2O or 7.5 mm Hg

In International System (SI) units, what is any quantity of matter that contains 6.023 1023 atoms, molecules, or ions? a. Pound (lb) b. Gram (g) c. Ounce (oz) d. Mole (mol)

ANS: D One mole of a gas, at a constant temperature and pressure, should occupy the same volume as 1 mol of any other gas. This ideal volume is termed the molar volume.

What is the common British unit of pressure? a. Newton (N)/m2 b. dyne/cm2 c. Pascal (Pa) d. lb/in2 (psi)

ANS: D Pounds per square inch (lb/in2), or "psi," is the British fps pressure unit.

Which of the following best describes the physical concept of pressure? a. Weight ÷ unit volume b. Mass acceleration c. Force distance d. Force ÷ unit area

ANS: D Pressure is a measure of force per unit area.

What force is responsible for the spherical shape of liquid droplets and their ability to keep this shape when placed into an aerosol suspension? a. Cohesion b. Adhesion c. Viscosity d. Surface tension

ANS: D Surface tension is a force exerted by like molecules at a liquid's surface. A small drop of fluid provides a good illustration of this force. Cohesive forces affect molecules inside the drop equally from all directions. However, only inward forces affect molecules on the surface. This imbalance in forces causes the surface film to contract into the smallest possible surface area, usually a sphere or curve (meniscus). This phenomenon explains why liquid droplets and bubbles retain a spherical shape.

If the absolute humidity in a medical gas being delivered to a patient is 14 mg/L, then what is the body humidity (BH)? a. 7% b. 16% c. 24% d. 32%

ANS: D The %BH of a gas is the ratio of its actual water vapor content to the water vapor capacity in saturated gas at body temperature (37 C). Thus %BH is the same as RH, except that the capacity (or denominator) is fixed at 43.8 mg/L

What physical principle underlies most fluidic circuitry? a. Poiseuille's law b. Bernoulli's principle c. Law of continuity d. Coanda effect

ANS: D The primary principle underlying most fluidic circuitry is a phenomenon called wall attachment, or the Coanda effect. This effect is observed mainly when a fluid flows through a small orifice with properly contoured downstream surfaces.

Which of the following methods would increase the rate of evaporation of a container of water? 1. Increase the temperature of the surrounding air. 2. Decrease the pressure of the surrounding air. 3. Increase the temperature of the water. 4. Decrease the pressure of the surrounding air. a. 1 and 3 only b. 2 and 4 only c. 2, 3, and 4 only d. 1, 2, and 3 only

ANS: D The warmer the air, the more vapor it can hold. Specifically, the capacity of air to hold water vapor increases with temperature. The warmer the air making contact with a water surface, the faster is the rate of evaporation.

Which of the following are true about molecular water vapor? 1. Water vapor exhibits kinetic activity. 2. Molecular water vapor can be seen. 3. Water vapor exerts pressure. a. 1 and 2 only b. 2 and 3 only c. 1, 2, and 3 d. 1 and 3 only

ANS: D To be distinguished from visible particulate water, such as mist or fog, this invisible gaseous form of water is called molecular water. Molecular water obeys the same physical principles as other gases and therefore exerts a pressure called water vapor pressure.

Which of the following properties of gases distinguish them from liquids—that is, are unique to the gaseous phase of matter? 1. Gases fill the available space. 2. Gases exhibit viscosity. 3. Gases exert pressure. 4. Gases are readily compressed. a. 2 and 3 only b. 1 and 3 only c. 2 and 4 only d. 1 and 4 only

ANS: D Unlike liquids, gases are readily compressed and expanded and fill the spaces available to them by diffusion.

Which of the following are true statements regarding evaporation? 1. Evaporation is a type of vaporization. 2. The process of evaporation warms the surrounding air. 3. Evaporation is the change of a liquid substance into a gas. 4. For evaporation to occur, heat energy is needed. a. 2 and 4 only b. 1, 2, and 3 only c. 1 and 3 only d. 1, 3, and 4 only

ANS: D Vaporization is the change of state from liquid to gas. Vaporization requires heat energy. According to the first law of thermodynamics, this heat energy must come from the surroundings. In one form of vaporization, called evaporation, heat is taken from the air surrounding the liquid, thereby cooling the air.

According to Bernoulli's principle, as a fluid flows through a narrow passage or stricture, which of the following will occur? 1. Fluid velocity will decrease. 2. Lateral pressure will fall. 3. Total energy will increase. a. 2 and 3 only b. 1 and 2 only c. 3 only d. 2 only

ANS: D When a fluid flows through a tube of uniform diameter, pressure decreases progressively over the tube length. When the fluid passes through a constriction, the pressure drop is much greater. This large pressure drop can be observed in the fourth water column in Figure 6-24. The eighteenth-century scientist Daniel Bernoulli was the first to carefully study this effect, which now bears his name. According to the law of continuity, as the fluid moves into the narrow or constricted portion of the tube, its velocity must increase (vb > va). According to the Bernoulli's theorem, the higher velocity at point b should result in a lower lateral pressure at that point (Pb < Pa). Thus, as a fluid flows through the constriction, its velocity increases and its lateral pressure decreases.

After placing a liquid into a small-diameter glass tube, you observe the formation of a convex (upwardly curved) meniscus. What conclusion is correct? a. The liquid must have a very low surface tension. b. Strong adhesive forces exist between the liquid and glass. c. The liquid must have an extremely high viscosity. d. Strong cohesive forces exist among the liquid molecules.

ANS: D When the liquid is water, the meniscus is concave because the water molecules at the surface adhere to the glass more strongly than they cohere to each other. In contrast, a mercury meniscus is convex. In this case, the cohesive forces pulling together the mercury atoms exceed the adhesive forces trying to attract the mercury to the glass.

Which of the following methods of heat transfer requires no direct contact between the warmer and cooler substances? a. Conduction b. Convection c. Evaporation d. Radiation

ANS: D While conduction and convection require direct contact between two substances, radiant heat transfer occurs without direct physical contact.

At a room temperature of 22 C, air has the capacity to hold 19.4 mg/L of water vapor. If the absolute humidity in the air is 7.4 mg/L, then what is the relative humidity (RH)? a. 45% b. 58% c. 70% d. 38%

ANS: D If the absolute humidity is 7.4 mg/L, then the RH is calculated as follows: %RH = 7.4 mg/L ÷ 19.4 mg/L 100 %RH = 0.38100 %RH = 38%