Heat Engineering / Refrigeration Fundamentals TP. Hồ Chí Minh HUIT University

Chapter 1: Fundamental Concepts of Units in Thermology Dynamics - Comprehensive Examination

100 questions

180 min

Answer key

Exam info

Subject: Heat Engineering / Refrigeration Fundamentals
Exam type: University
Questions: 100
Duration: 180 min
Answers: ✓ With explanations
School: Đại học Công nghiệp TP.HCM (HUIT)

Questions (100)

Q 1.
A refrigeration engineer in Japan, working with the conventional metric system, needs to determine the mass of water that has the same mass as a 16 oz container of refrigerant. Using the conversion factor provided in Table 1-1, which of the following is the correct mass in kilograms?
- A.
  0.4536 kg
- B.
  0.4536 × 16 kg
- C.
  0.00226 kg
- D.
  16 × 2.205 kg
Q 2.
According to the textbook, the reason the International System of Units (SI) has not been fully adopted in the Japan Refrigeration and Air Conditioning textbook is primarily because:
- A.
  It is too early to adopt the SI metric system fully in the textbook, as the system is not used in gauge products.
- B.
  The yard-pound system is fundamentally incompatible with thermodynamic analysis.
- C.
  SI units cannot express pressure values above 1 atmosphere accurately.
- D.
  Japan has officially rejected the SI metric system by international treaty.
Q 3.
An object has a mass of 250 g on a calibrated scale. Using the textbook's conversion methodology, what is the equivalent mass in ounces (oz)?
- A.
  8.82 oz
- B.
  0.03527 × 0.25 oz
- C.
  28.35 oz
- D.
  8.82 × 16 oz
Q 4.
A technician weighs a copper coil and finds it has a mass of 1.36 kg. According to the textbook's examples and Table 1-1, what is the equivalent mass in pounds (lb)?
- A.
  3.00 lb
- B.
  0.62 lb
- C.
  1.36 lb
- D.
  2.9988 kg
Q 5.
The textbook defines mass as a fundamental property of an object that is a numerical measure of its inertia. Which of the following statements about mass, as described in the chapter, is most accurate?
- A.
  Mass is normally considered an unchanging property of an object, but at speeds approaching the speed of light, one must consider the increase in relativistic mass.
- B.
  Mass is defined as the force exerted on an object by Earth's gravitational field.
- C.
  Mass changes with location on Earth because gravitational acceleration varies.
- D.
  The SI unit of mass is the gram, defined as 1 cm³ of mercury at its densest point.
Q 6.
A laboratory has 5 lb of dry ice. Using the conversion formulae provided, what is the equivalent mass in kilograms?
- A.
  2.27 kg
- B.
  0.4536 × 5 × 2.205 kg
- C.
  0.9072 kg
- D.
  5 × 28.35 kg
Q 7.
Which of the following is the textbook's stated relationship for converting kilograms to ounces directly (using the provided conversion factor)?
- A.
  oz = 35.27 × kg
- B.
  oz = 0.03527 × kg
- C.
  oz = 0.0625 × kg
- D.
  oz = 2.205 × kg
Q 8.
According to the textbook, why is mass considered 'such a fundamental quantity that it is hard to define in terms of something else'?
- A.
  Because definitions of mass often seem circular since all mechanical quantities are defined in terms of mass, length, and time.
- B.
  Because mass varies significantly with temperature in all materials.
- C.
  Because mass is dependent on the gravitational field strength at the measurement location.
- D.
  Because mass is measured only with very imprecise instruments in everyday use.
Q 9.
According to the textbook's definition of a kilogram force (kgf), a 1 kg mass experiences gravitational acceleration of approximately 9.807 m/s². Which of the following is the textbook's definition of a kilogram force?
- A.
  A kilogram force is the force of gravity of an object having a mass of 1 kg.
- B.
  A kilogram force is the force required to accelerate a 1 kg mass to a velocity of 1 m/s.
- C.
  A kilogram force is the force exerted by a 1 kg mass under standard atmospheric pressure.
- D.
  A kilogram force is 4.448 times the magnitude of one pound force.
Q 10.
What is the textbook's precise statement for a Newton (N) in terms of mass, distance, and time?
- A.
  1 N = 1 kg·m/s², meaning if a force of 1 N is exerted on a 1 kg mass for 1 s, the mass ends up with a velocity of 1 m/s.
- B.
  1 N = 1 kg·m/s, indicating the velocity per unit mass.
- C.
  1 N is the gravitational pull on a 1 kg mass at the Earth's surface.
- D.
  1 N equals 1 kgf under all gravitational conditions.
Q 11.
From Table 1-2, how many Newton (N) correspond to exactly 1 kilogram force (kgf)?
- A.
  9.807 N
- B.
  0.1020 N
- C.
  2.205 N
- D.
  4.448 N
Q 12.
What is the relationship between 1 pound force (lbf) and 1 Newton (N) as given in Table 1-2?
- A.
  1 lbf = 4.448 N
- B.
  1 lbf = 0.4536 N
- C.
  1 lbf = 9.807 N
- D.
  1 lbf = 2.205 N
Q 13.
A textbook example states that if a force of 1 N is applied to a mass of 1 kg for 1 second, the resulting velocity is 1 m/s. Which fundamental physical relationship does this illustrate?
- A.
  Newton's second law, F = ma.
- B.
  Pascal's principle of fluid transmission.
- C.
  Newton's law of universal gravitation.
- D.
  The Stefan-Boltzmann law of radiation.
Q 14.
The textbook defines weight (W) using the relationship W = m·g_e. Which of the following is the textbook's value for g_e at Earth's surface?
- A.
  9.8 m/s² (or equivalently 32.2 ft/s²).
- B.
  1.033 m/s², equal to one atmospheric pressure unit.
- C.
  735.6 m/s², the textbook's pressure conversion factor.
- D.
  9.807 × 10⁻⁸ m/s², the Stefan-Boltzmann constant.
Q 15.
A refrigeration unit's compressor has a mass of 12 kg. Using g_e = 9.807 m/s², what is its weight in Newtons?
- A.
  117.7 N
- B.
  12 N
- C.
  1.224 kgf
- D.
  117.7 kgf
Q 16.
The textbook notes a custom to abbreviate 'kilogram force' as 'kilogram' and 'pound force' as 'pound', with symbols 'kgf' as 'kg' and 'lbf' as 'lb'. What is the practical implication of this convention for service technicians?
- A.
  Almost all weighing apparatus indicate units of mass, so technicians must remember the abbreviation when reading gauge pressures.
- B.
  Technicians must use only SI units and abandon the conventional metric system entirely.
- C.
  The yard-pound system should not be used for industrial refrigeration calculations.
- D.
  Mass and weight can be used interchangeably because of the abbreviations.
Q 17.
Given the gravitational equation F = G·(m₁·m₂)/d², the textbook simplifies this for Earth as W_e = m·g_e. Which value of g_e does the textbook use?
- A.
  9.8 m/s² or 32.2 ft/s²
- B.
  10 m/s² (approximated for engineering calculations)
- C.
  0.4536 m/s² corresponding to 1 lb
- D.
  1.033 m/s² corresponding to atmospheric pressure
Q 18.
An object with mass m is located on the Moon, where gravitational acceleration is approximately 1/6 of Earth's g_e. If its mass is 60 kg, what is its weight on the Moon (using the textbook's framework)?
- A.
  60 × 9.807/6 ≈ 98.07 N
- B.
  60 N
- C.
  60 × 9.807 N
- D.
  10 kg
Q 19.
According to the textbook, pressure is defined as:
- A.
  The force exerted on a unit area, P = F/A.
- B.
  The mass of fluid above a given point.
- C.
  The volume occupied by a fluid per unit mass.
- D.
  The temperature change caused by force application.
Q 20.
Which unit of pressure is associated with the conventional metric system as discussed in the textbook?
- A.
  kgf/cm²
- B.
  Pascal (Pa)
- C.
  psi (lb/in²)
- D.
  Newton per square meter
Q 21.
A 5 kgf solid rests on a flat surface with a bottom area of 5 cm². What pressure does it exert, using the textbook's convention?
- A.
  1 kgf/cm²
- B.
  25 kgf/cm²
- C.
  0.2 kgf/cm²
- D.
  5 kgf/cm²
Q 22.
The Pascal (Pa) is defined in the textbook as:
- A.
  A Newton per square meter.
- B.
  A kilogram force per square centimeter.
- C.
  A pound per square inch.
- D.
  One kilogram mass times gravity.
Q 23.
What is the relationship between 1 kPa and 1 Pa as given in the textbook?
- A.
  1 kPa = 1000 Pa
- B.
  1 kPa = 0.001 Pa
- C.
  1 kPa = 100 Pa
- D.
  1 kPa = 9.807 Pa
Q 24.
According to the textbook, what does Pascal's Law state?
- A.
  Pressure applied on a confined fluid is transmitted equally in all directions.
- B.
  Pressure at the bottom of a fluid column is equal to atmospheric pressure plus the fluid's weight.
- C.
  The buoyant force on an object equals the weight of the displaced fluid.
- D.
  Gas pressure is inversely proportional to its volume at constant temperature.
Q 25.
The textbook illustrates Pascal's Law using a fluid-filled cylinder with chambers of different shapes. What key observation do the pressure gauges in this demonstration show?
- A.
  Pressure is transmitted equally in all directions and chambers regardless of chamber size or shape.
- B.
  Pressure decreases as the chamber cross-section expands.
- C.
  Pressure increases with depth in the fluid.
- D.
  Pressure is greatest in the smallest cross-section chamber.
Q 26.
The textbook defines atmospheric pressure as the force exerted by the weight of the air column above a given area. At sea level, the textbook states that a 1 cm² column of air from sea level to the top of the atmosphere weighs approximately:
- A.
  1.033 kgf (or 14.70 lbf)
- B.
  0.4536 kgf, equivalent to 1 lb.
- C.
  9.807 kgf, the weight of a 1 kg mass under Earth's gravity.
- D.
  760 kgf, the standard mercury column weight.
Q 27.
Which of the following expresses atmospheric pressure according to the textbook's equivalences?
- A.
  1 atm = 1.033 kgf/cm² = 760 mmHg = 101.3 kPa = 14.70 lbf/in² = 29.92 in.Hg
- B.
  1 atm = 14.22 kgf/cm² = 0.9678 mmHg
- C.
  1 atm = 100 Pa = 1.033 psi
- D.
  1 atm = 0 kgf/cm², since atmospheric is the reference zero.
Q 28.
The textbook defines 'partial vacuum' and 'perfect vacuum'. Which of the following statements is correct?
- A.
  Partial vacuum is a pressure lower than atmospheric pressure, but not a perfect vacuum; perfect vacuum cannot be reduced further.
- B.
  Partial vacuum is a pressure higher than atmospheric pressure.
- C.
  Perfect vacuum is a pressure equal to atmospheric pressure.
- D.
  Partial vacuum refers to atmospheric pressure itself.
Q 29.
How does the textbook express a perfect vacuum in multiple units?
- A.
  0 kgf/cm² = 0 mmHg = 0 Pa = 0 psi = 0 in.Hg
- B.
  1 atm = 760 mmHg = 14.7 psi
- C.
  1.033 kgf/cm² = 101.3 kPa = 29.92 in.Hg
- D.
  Negative atmospheric pressure values
Q 30.
The textbook notes that a simple barometer uses mercury. Under standard conditions at sea level, the height of the mercury column is:
- A.
  760 mm (29.92 in)
- B.
  1.033 mm (29.92 cm)
- C.
  735.6 mm (the conversion factor from kgf/cm²)
- D.
  100 mm (100 mmHg = 1 kPa)
Q 31.
According to the textbook's conversion formula, how do you convert 25 kgf/cm² into atmospheres (atm)?
- A.
  atm = 0.9678 × 25 ≈ 24.20 atm
- B.
  atm = 25 / 1.033 ≈ 24.20 atm
- C.
  atm = 1.033 × 25 ≈ 25.83 atm
- D.
  atm = 735.6 × 25 ≈ 18390 atm
Q 32.
Convert 3.5 atm into kgf/cm² using the textbook's formula:
- A.
  kgf/cm² = 1.033 × 3.5 ≈ 3.62 kgf/cm²
- B.
  kgf/cm² = 0.9678 × 3.5 ≈ 3.39 kgf/cm²
- C.
  kgf/cm² = 14.22 × 3.5 ≈ 49.77 kgf/cm²
- D.
  kgf/cm² = 735.6 × 3.5 ≈ 2574.6 kgf/cm²
Q 33.
Convert 800 mmHg into kgf/cm² using the textbook's formula:
- A.
  kgf/cm² = 0.001360 × 800 ≈ 1.088 kgf/cm²
- B.
  kgf/cm² = 735.6 × 800
- C.
  kgf/cm² = 1.033 × 800
- D.
  kgf/cm² = 0.9678 × 800
Q 34.
Convert 15 kgf/cm² into psi using the textbook's formula:
- A.
  psi = 14.22 × 15 ≈ 213.3 psi
- B.
  psi = 0.07031 × 15 ≈ 1.05 psi
- C.
  psi = 0.1450 × 15 ≈ 2.18 psi
- D.
  psi = 98.07 × 15 ≈ 1471 psi
Q 35.
Convert 250 kPa into psi using the textbook's conversion table:
- A.
  psi = 0.1450 × 250 = 36.25 psi
- B.
  psi = 6.895 × 250 = 1723.75 psi
- C.
  psi = 14.22 × 250 = 3555 psi
- D.
  psi = 98.07 × 250 ≈ 24518 psi
Q 36.
Convert 40 psi into kPa using the textbook's formula:
- A.
  kPa = 6.895 × 40 = 275.8 kPa
- B.
  kPa = 0.1450 × 40 = 5.8 kPa
- C.
  kPa = 14.22 × 40 = 568.8 kPa
- D.
  kPa = 0.07031 × 40 = 2.81 kPa
Q 37.
What is the textbook's definition of gauge pressure?
- A.
  Gauge pressure is the pressure as indicated by a gauge, calibrated to read zero at atmospheric pressure, measuring only the difference between fluid pressure and atmospheric pressure.
- B.
  Gauge pressure is the total or true pressure of a fluid, including atmospheric pressure.
- C.
  Gauge pressure is the pressure measured by a barometer at sea level.
- D.
  Gauge pressure is the pressure in a perfect vacuum.
Q 38.
The textbook defines absolute pressure as the 'total' or true pressure of a fluid. If a fluid's absolute pressure is greater than atmospheric pressure, the absolute pressure equals:
- A.
  Atmospheric pressure plus gauge pressure.
- B.
  Atmospheric pressure minus gauge pressure.
- C.
  Gauge pressure only.
- D.
  Twice the atmospheric pressure.
Q 39.
A refrigerant line shows a gauge pressure of 5 kgf/cm². Using the textbook's framework and atmospheric pressure of 1.033 kgf/cm², what is the absolute pressure?
- A.
  6.033 kgf/cm² abs
- B.
  5 kgf/cm² abs
- C.
  3.967 kgf/cm² abs
- D.
  1.033 kgf/cm² abs
Q 40.
What is the textbook's definition of 'heat'?
- A.
  Heat is a form of energy related to molecular motion or vibration; molecules move more rapidly when warmed and stop moving if all heat is removed.
- B.
  Heat is a measure of the temperature of an object.
- C.
  Heat is the weight of the molecules in a substance.
- D.
  Heat is the volume occupied by molecules in motion.
Q 41.
Which of the following is the textbook's stated direction of heat flow?
- A.
  Heat always flows from a warmer substance to a cooler one.
- B.
  Heat always flows from a cooler substance to a warmer one.
- C.
  Heat can flow in any direction depending on the substance.
- D.
  Heat does not flow; only temperature changes.
Q 42.
According to the textbook, heat transfer always occurs from a hot body to a cold one as a result of which law?
- A.
  The second law of thermodynamics.
- B.
  Newton's first law of motion.
- C.
  Pascal's law.
- D.
  Archimedes' principle.
Q 43.
What does the textbook say about whether heat transfer can be stopped?
- A.
  Heat transfer can never be stopped; it can only be slowed down.
- B.
  Heat transfer can be completely stopped by perfect insulation.
- C.
  Heat transfer can be reversed by applying external work.
- D.
  Heat transfer only occurs in liquids, not solids.
Q 44.
The textbook lists three modes of heat transfer. Which of the following is NOT one of them according to section 1.2.4.2?
- A.
  Sublimation
- B.
  Conduction
- C.
  Convection
- D.
  Radiation
Q 45.
According to the textbook's radiation formula H = e·σ·A·T⁴, the constant σ (Stefan-Boltzmann constant) is:
- A.
  5.67 × 10⁻⁸ J/(s·m²·K⁴)
- B.
  9.807 J/(s·m²·K⁴)
- C.
  0.4536 J/(s·m²·K⁴)
- D.
  1.033 × 10⁻⁸ J/(s·m²·K⁴)
Q 46.
In the textbook's conduction formula Q/t = (k·A·(T_hot - T_cold))/d, what does the variable 'k' represent?
- A.
  Thermal conductivity of the barrier.
- B.
  Kinetic energy of the molecules.
- C.
  Boltzmann's constant.
- D.
  Specific heat capacity.
Q 47.
Convection, as defined in the textbook, involves:
- A.
  Heat transfer by mass motion of a fluid such as air or water, carrying energy with it.
- B.
  Heat transfer through electromagnetic waves without intervening matter.
- C.
  Heat transfer by molecular agitation within a stationary material.
- D.
  Heat transfer that only occurs in solids.
Q 48.
What is the textbook's definition of a calorie (cal)?
- A.
  The amount of heat required to raise the temperature of 1 g of water by 1°C.
- B.
  The amount of heat required to raise the temperature of 1 kg of water by 1°C.
- C.
  The amount of heat required to raise the temperature of 1 lb of water by 1°F.
- D.
  A measure of the temperature of water.
Q 49.
What is the relationship between 1 cal and Joules as given in the textbook?
- A.
  1 cal = 4.186 J
- B.
  1 cal = 1000 J
- C.
  1 cal = 1 J
- D.
  1 cal = 0.001 J
Q 50.
Convert 7500 cal into kcal using the textbook's conversion:
- A.
  7.5 kcal
- B.
  7500 kcal
- C.
  0.75 kcal
- D.
  7,500,000 kcal
Q 51.
Convert 8 kcal into kJ using the textbook's conversion factor:
- A.
  kJ = 4.186 × 8 = 33.49 kJ
- B.
  kJ = 0.2389 × 8 = 1.91 kJ
- C.
  kJ = 8 × 1000 = 8000 kJ
- D.
  kJ = 8 × 1.055 = 8.44 kJ
Q 52.
Convert 500 kJ into kcal using the textbook's formula:
- A.
  kcal = 0.2389 × 500 = 119.45 kcal
- B.
  kcal = 4.186 × 500 = 2093 kcal
- C.
  kcal = 500 / 1000 = 0.5 kcal
- D.
  kcal = 1.055 × 500 = 527.5 kcal
Q 53.
What is the textbook's definition of a British thermal unit (Btu)?
- A.
  The amount of heat required to raise the temperature of 1 lb of water by 1°F.
- B.
  The amount of heat required to raise the temperature of 1 g of water by 1°C.
- C.
  The amount of heat required to raise the temperature of 1 kg of water by 1°C.
- D.
  The amount of heat required to raise the temperature of 1 lb of water by 1°C.
Q 54.
Convert 4000 Btu into kcal using the textbook's conversion factor:
- A.
  kcal = 0.2520 × 4000 = 1008 kcal
- B.
  kcal = 3.968 × 4000 = 15872 kcal
- C.
  kcal = 1.055 × 4000 = 4220 kcal
- D.
  kcal = 0.9480 × 4000 = 3792 kcal
Q 55.
What does the textbook state about the relationship between temperature and heat?
- A.
  Temperature measures heat intensity or heat level; temperature alone does not give the amount of heat in a substance.
- B.
  Temperature and heat are the same physical quantity with different names.
- C.
  Heat is a measure of temperature, but not the other way around.
- D.
  Temperature measures the amount of heat, while heat measures the intensity.
Q 56.
On the Celsius (centigrade) scale, the freezing and boiling points of water at standard atmospheric pressure are:
- A.
  0°C and 100°C, with 100 divisions between them.
- B.
  32°C and 212°C, with 180 divisions between them.
- C.
  273°C and 373°C, with 100 divisions between them.
- D.
  -273°C and 100°C, with 373 divisions.
Q 57.
On the Fahrenheit scale, the freezing and boiling points of water at standard atmospheric pressure are:
- A.
  32°F and 212°F, with 180 divisions between them.
- B.
  0°F and 100°F, with 100 divisions between them.
- C.
  32°F and 100°F, with 68 divisions between them.
- D.
  0°F and 212°F, with 212 divisions between them.
Q 58.
What is the textbook's definition of absolute zero?
- A.
  The temperature at which molecular motion stops; the lowest temperature possible, with no heat remaining in the substance.
- B.
  The temperature at which water freezes under standard atmospheric pressure.
- C.
  The temperature at which all gases become liquids.
- D.
  The temperature of boiling water at sea level.
Q 59.
According to the textbook, the Kelvin scale is offset from Celsius by:
- A.
  Zero on the Kelvin scale is 273 degrees below 0°C.
- B.
  Zero on the Kelvin scale is 273 degrees above 0°C.
- C.
  Zero on the Kelvin scale equals 0°C.
- D.
  Zero on the Kelvin scale equals -100°C.
Q 60.
What is the offset between the Rankine and Fahrenheit scales according to the textbook?
- A.
  Zero on the Rankine scale is 460 degrees below 0°F.
- B.
  Zero on the Rankine scale is 460 degrees above 0°F.
- C.
  Zero on the Rankine scale equals 0°F.
- D.
  Zero on the Rankine scale equals 273°F.
Q 61.
Convert 80°C into Fahrenheit using the textbook's formula:
- A.
  176°F
- B.
  144°F
- C.
  112°F
- D.
  80°F
Q 62.
Convert -10°F into Celsius using the textbook's formula:
- A.
  C = (5/9) × (-10 - 32) = (5/9) × (-42) = -23.33°C
- B.
  C = (5/9) × (-10) = -5.56°C
- C.
  C = (9/5) × (-10) + 32 = 14°F
- D.
  C = -10°C
Q 63.
Convert 50°C into Kelvin using the textbook's formula:
- A.
  323 K
- B.
  223 K
- C.
  50 K
- D.
  273 K
Q 64.
Convert 350 K into Celsius using the textbook's formula:
- A.
  77°C
- B.
  623°C
- C.
  350°C
- D.
  -77°C
Q 65.
Convert 60°F into Rankine using the textbook's formula:
- A.
  520 R
- B.
  400 R
- C.
  60 R
- D.
  460 R
Q 66.
Convert 100 R into Fahrenheit using the textbook's formula:
- A.
  -360°F
- B.
  560°F
- C.
  100°F
- D.
  360°F
Q 67.
What is the textbook's definition of dry-bulb temperature?
- A.
  The temperature determined by an ordinary thermometer, not affected by vapor content or relative humidity, measuring 'sensible heat'.
- B.
  The temperature at which air becomes saturated with water vapor.
- C.
  The lowest temperature a water film can assume when evaporating into air.
- D.
  The total heat content of air.
Q 68.
What is the textbook's definition of dew point temperature?
- A.
  The temperature at which air becomes saturated with water vapor and the vapor condenses as drops of water (dew).
- B.
  The temperature at which ice forms directly from vapor without passing through liquid phase.
- C.
  The temperature measured by a thermometer with a wet cloth covering the bulb.
- D.
  The temperature of dry air measured by an ordinary thermometer.
Q 69.
According to the textbook, what is the relative humidity at the dew point?
- A.
  100%
- B.
  50%
- C.
  0%
- D.
  It depends on the ambient temperature.
Q 70.
What is the textbook's definition of wet-bulb temperature?
- A.
  The temperature of evaporation; the lowest temperature a surface film of water can assume when evaporating freely into air.
- B.
  The temperature at which air becomes saturated with water vapor.
- C.
  The temperature measured by an ordinary thermometer unaffected by humidity.
- D.
  The boiling point of water at standard pressure.
Q 71.
According to the textbook, if the air is saturated (raining or heavy fog), the dry-bulb and wet-bulb temperatures will be:
- A.
  Equal
- B.
  Wet-bulb higher than dry-bulb
- C.
  Dry-bulb higher by 10°C
- D.
  Unrelated to each other
Q 72.
What is the textbook's definition of humidity?
- A.
  Moisture in the air; the ability of air to hold moisture directly relates to its temperature.
- B.
  The temperature of air.
- C.
  The mass of air per unit volume.
- D.
  The pressure exerted by water vapor in the air.
Q 73.
According to the textbook, how does relative humidity relate to the air's moisture capacity?
- A.
  It is the percentage of moisture in the air compared to the amount of moisture the air can hold.
- B.
  It is the absolute amount of moisture in the air in grams.
- C.
  It is independent of the air's temperature.
- D.
  It is always 100% at all temperatures.
Q 74.
How does the textbook describe humidity as a form of heat?
- A.
  Humidity is a form of latent heat; more humid air contains more latent heat.
- B.
  Humidity is a form of sensible heat.
- C.
  Humidity is unrelated to heat.
- D.
  Humidity is a form of work.
Q 75.
What does the textbook state about sweat evaporation at low versus high humidity?
- A.
  At low humidity, sweat evaporates more quickly, allowing faster cooling; at high humidity, sweat evaporates less effectively.
- B.
  Sweat evaporation is the same regardless of humidity.
- C.
  Sweat evaporation is faster at high humidity.
- D.
  Sweat does not evaporate at all at any humidity.
Q 76.
What is the textbook's definition of work?
- A.
  Force multiplied by the distance through which it travels.
- B.
  Energy stored in a system.
- C.
  The rate of energy transfer per unit time.
- D.
  The mass of a moving object.
Q 77.
What is the textbook's definition of energy?
- A.
  The capacity or ability to do work.
- B.
  The rate at which work is performed.
- C.
  The temperature of an object.
- D.
  The weight of an object.
Q 78.
According to the textbook, in a refrigeration unit, electrical energy flowing into the electric motor is converted into:
- A.
  Mechanical energy, which then turns the compressor; the compressor then transforms mechanical energy into heat energy by compressing vapor.
- B.
  Direct heat energy without intermediate mechanical conversion.
- C.
  Light energy.
- D.
  Chemical energy stored in refrigerant.
Q 79.
What is the textbook's definition of power?
- A.
  The time rate of doing work.
- B.
  The total amount of work done.
- C.
  The distance moved per unit time.
- D.
  The mass moved per unit time.
Q 80.
According to the textbook, substances exist in three physical states. Under standard atmospheric pressure, water transitions between these states at which temperatures?
- A.
  Below 0°C (32°F): solid; 0°C to 100°C: liquid; above 100°C: gas/vapor.
- B.
  Below 32°F only: solid; otherwise always gas.
- C.
  Below 100°C: solid; above 100°C: liquid; at 100°C: gas.
- D.
  Below 273 K: gas; 273-373 K: solid; above 373 K: liquid.
Q 81.
What is the textbook's term for the phase change from solid to liquid?
- A.
  Fusion
- B.
  Sublimation
- C.
  Vaporization
- D.
  Condensation
Q 82.
What is the textbook's term for the phase change from solid directly to gas?
- A.
  Sublimation
- B.
  Fusion
- C.
  Condensation
- D.
  Solidification
Q 83.
According to the textbook, the reverse process of vaporization (when heat is removed) is called:
- A.
  Condensation
- B.
  Fusion
- C.
  Sublimation
- D.
  Solidification
Q 84.
What is the textbook's definition of saturated liquid?
- A.
  A liquid at its saturation temperature; any additional heat will cause a portion to vaporize.
- B.
  A liquid that contains no dissolved gases.
- C.
  A liquid at a temperature below its saturation temperature.
- D.
  A liquid that has been superheated.
Q 85.
What is the textbook's definition of superheated vapor?
- A.
  Vapor at a temperature above its saturation temperature, separated from the vaporizing liquid.
- B.
  Vapor at its saturation temperature.
- C.
  Vapor that has been condensed to liquid.
- D.
  Vapor mixed with sub-cooled liquid.
Q 86.
What is the textbook's definition of sub-cooled liquid?
- A.
  Liquid that has been cooled below its saturation temperature after condensation.
- B.
  Liquid at its saturation temperature.
- C.
  Liquid that has been superheated.
- D.
  Liquid that has fully vaporized.
Q 87.
According to the textbook, water boils at 100°C at atmospheric pressure. At what temperature does alcohol vaporize under the same atmospheric pressure?
- A.
  78°C
- B.
  100°C
- C.
  -40.8°C
- D.
  0°C
Q 88.
What does the textbook state about the saturation temperature of refrigerant R-22 under atmospheric pressure?
- A.
  R-22 vaporizes at -40.8°C under atmospheric pressure.
- B.
  R-22 vaporizes at 100°C under atmospheric pressure.
- C.
  R-22 vaporizes at 78°C under atmospheric pressure.
- D.
  R-22 has no saturation temperature.
Q 89.
According to the textbook, how does increasing pressure affect the saturation temperature of a substance?
- A.
  Increasing the pressure raises the saturation temperature.
- B.
  Increasing the pressure lowers the saturation temperature.
- C.
  Saturation temperature is independent of pressure.
- D.
  The relationship depends on the substance's color.
Q 90.
The textbook gives an example: at 1.03 kgf/cm² abs, water's saturation temperature is 100°C. If the pressure is increased to 2.0 kgf/cm² abs, what happens to the saturation temperature?
- A.
  The saturation temperature increases above 100°C.
- B.
  The saturation temperature decreases below 100°C.
- C.
  The saturation temperature stays at 100°C.
- D.
  The water becomes solid.
Q 91.
What does the textbook define as 'sensible heat'?
- A.
  Heat that causes a change in temperature in a substance when added or removed.
- B.
  Heat that causes a change of state without a change in temperature.
- C.
  Heat stored at absolute zero.
- D.
  Heat measured by a thermometer only.
Q 92.
What does the textbook define as 'latent heat'?
- A.
  Heat that brings about a change of state with no change in temperature.
- B.
  Heat that increases the temperature of a substance.
- C.
  Heat measured by a barometer.
- D.
  Heat stored in absolute vacuum.
Q 93.
Using the textbook's example, calculate the sensible heat (in kcal) required to heat 5 kg of copper from 20°C to 220°C, given copper's specific heat ≈ 0.095 kcal/(kg·°C).
- A.
  95 kcal
- B.
  0.95 kcal
- C.
  950 kcal
- D.
  19 kcal
Q 94.
What is the specific heat of water according to the textbook's Table 1-6?
- A.
  1 kcal/(kg·°C) or 4.187 kJ/(kg·K)
- B.
  0.504 kcal/(kg·°C)
- C.
  0.327 kcal/(kg·°C)
- D.
  0.129 kcal/(kg·°C)
Q 95.
The textbook gives an example of heating 1 kg of water from -50°C ice to 150°C vapor under atmospheric pressure. The latent heat of vaporization (D to E) is approximately:
- A.
  539 kcal
- B.
  79.6 kcal
- C.
  100 kcal
- D.
  25.2 kcal
Q 96.
According to the textbook's Table 5, what is the latent heat of vaporization of water at 100°C?
- A.
  2260 J/g
- B.
  334 J/g
- C.
  855 J/g
- D.
  1369 J/g
Q 97.
A refrigeration engineer uses the formula Q = m·L to calculate the heat required to vaporize 10 kg of water at 100°C. With L = 539 kcal/kg, what is the heat Q?
- A.
  5390 kcal
- B.
  539 kcal
- C.
  53.9 kcal
- D.
  53,900 kcal
Q 98.
Using the textbook's formula for sensible heat Q_s = M·C·(t₂ - t₁), how much heat (in kcal) is required to heat 20 kg of water from 30°C to 80°C? Water's specific heat is 1 kcal/(kg·°C).
- A.
  1000 kcal
- B.
  1100 kcal
- C.
  50 kcal
- D.
  2000 kcal
Q 99.
Essay: A refrigeration system operates with R-22 refrigerant. At one point in the cycle, R-22 vapor is at 30°C under a saturation pressure where the saturation temperature is -5°C. Using the textbook's superheat formula, calculate the amount of superheat, explain what superheat means in terms of phase state, and discuss why superheat is important for safe compressor operation.
Q 100.
Essay: A copper block of 20 kg is to be heated from 30°C to 250°C. Using the textbook's sensible heat formula and the example for copper (specific heat ≈ 0.095 kcal/(kg·°C)), calculate the heat required in kcal. Then, convert the heat in kcal to (a) Btu, (b) kJ, and (c) Joules. Discuss the practical relevance of these energy conversions for a refrigeration engineer who must select equipment for a specific climate application.

Answers and explanations are in mode.