PTEC 131 - Exam 2 - Fall 14

Liquids and gases are considered fluids because they both have the ability to flow and take the shape of their container. When calculating pressure, both liquids and gases are treated as fluids because they exert pressure in all directions. This is due to the fact that the particles in fluids are not held together in a rigid structure like solids, allowing them to move more freely. Therefore, it is correct to say that when calculating pressure, liquids and gases are considered as fluids.

The correct answer is 18.7. According to the conversion chart, to convert psig to psia, you add 14.7. Therefore, 4 psig + 14.7 = 18.7 psia.

Fluids are substances that have the ability to flow and take the shape of their container. Liquids and gases both possess these characteristics, which is why they are considered to be fluids. Liquids, such as water and oil, flow freely and take the shape of their container. Gases, such as air and helium, also flow easily and fill the space they are in. Therefore, the statement that liquid and gases are considered to be fluids is correct.

A strain gauge transducer is a pressure measuring device that consists of a group of wires that stretch when pressure is applied. As the wires stretch, their resistance changes, allowing the transducer to measure the applied pressure. This type of transducer is commonly used in various industries for measuring pressure in applications such as automotive, aerospace, and industrial processes.

The correct answer is 2.69. To convert inches H2O to psig, we use the conversion factor of 27.7. So, we multiply 74.7 inches H2O by 27.7 to get the equivalent pressure in psig, which is 2069.19 psig. Therefore, the correct answer is 2.69.

A manometer is a pressure measuring device that uses a U-shaped tube with two fluid chambers. The pressure difference between the two chambers causes the fluid to rise or fall in the tube, indicating the pressure being measured. This type of device is commonly used to measure the pressure of gases or liquids in various applications. Capacitance transducers, differential pressure cells, and strain gauge transducers are different types of pressure measuring devices that operate on different principles and are not specifically designed with a U-shaped tube.

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The given formula to calculate pressure, P = F - V, is incorrect. The correct formula to calculate pressure is P = F / A, where P represents pressure, F represents force, and A represents area. Therefore, the correct answer is false.

The statement is true because the Greek letter delta (∆) is commonly used to represent the concept of "change" or "difference" in mathematics and science. In the context of expressing differential pressure, the delta symbol is used to indicate the difference between two pressure values. Additionally, the abbreviation d/p is also commonly used to represent differential pressure, where "d" stands for delta and "p" represents pressure. Therefore, both the Greek letter delta and the abbreviation d/p are indeed common ways to express differential pressure.

A manometer and gauge are two examples of local indicators because they provide measurements or indications of pressure or other variables in the immediate vicinity or location where they are installed. They do not provide remote or distant measurements and are typically used for monitoring or controlling processes within a specific area or system.

A differential pressure cell is used to measure the difference between two pressure points. It consists of two pressure chambers connected to a diaphragm. When the pressure difference between the two points changes, it causes the diaphragm to flex, which can be measured and converted into an electrical signal. This makes the differential pressure cell a suitable instrument for accurately measuring and monitoring pressure differences in various applications, such as flow rate measurement, level measurement, and HVAC systems.

To convert 100 inches H2O to psig, we can use the conversion factor given in the chart: psig x 27.7 = inches of H2O. Rearranging the equation, we have inches of H2O = psig / 27.7. Plugging in the value of 100 inches H2O, we get 100 / 27.7 = 3.61 psig. Therefore, the correct answer is 3.61.

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In the equation P=F/A, F represents force. Force is a physical quantity that is measured in units such as Newtons (N) or pounds (lb). In this equation, force is divided by the area (A) to calculate the pressure (P). Therefore, F represents the force exerted on a given area.

A differential pressure cell is a type of sensor that can be either a simple mechanical type or a more advanced transducer type. It is commonly found in both pneumatic and electronic transmitters. The sensor produces an output signal of 3 to 15 psi, which makes it suitable for measuring and detecting the difference in pressure between two points. This allows for accurate measurement of flow rates, level, and other variables in various industrial applications.

Density is a measure of how much mass is contained in a given volume. It is calculated by dividing the mass of an object by its volume. Therefore, density represents the mass per unit volume of a substance. Specific gravity, pressure, and force are not directly related to mass per unit volume and do not provide information about the concentration of mass within a given volume.

To convert 50 inches H2O to psig, we can use the conversion factor given in the chart: psig = inches of H2O x 27.7. By substituting the given value of 50 inches H2O into the equation, we get 50 x 27.7 = 1385 psig. Therefore, the correct answer is 1385.

To convert 235 inches H2O to inches Hg, we can use the conversion factor of 2.04. By multiplying 235 by 2.04, we get the answer of 478.2 inches Hg.

Transmitters are generally considered to be transducers. Transducers are devices that convert one form of energy into another, such as converting physical quantities into electrical signals. Transmitters, in particular, are devices that convert physical measurements or signals into electrical signals for transmission to a receiving device. Therefore, it can be inferred that transmitters are a type of transducer.

Pressure is defined as the force applied to a unit area. This means that pressure is the amount of force exerted on a surface divided by the area over which the force is applied. It is commonly measured in units such as pounds per square inch (psi) or pascals (Pa). This definition helps to understand how pressure is calculated and how it affects objects and their surroundings.

Atmospheric pressure at sea level is measured to be 14.7 PSIA. This value is commonly referred to as standard atmospheric pressure and is the average pressure exerted by the Earth's atmosphere at sea level. It is important to note that atmospheric pressure can vary slightly depending on factors such as weather conditions and altitude, but 14.7 PSIA is considered the standard value at sea level.

To convert inches H2O to inches Hg, we can use the conversion factor of 2.04. Therefore, the conversion is calculated by multiplying the known units (5 inches H2O) by the conversion factor (2.04). This gives us a result of 10.20 inches Hg. Therefore, the correct answer is 10.20.

Gauge pressure always sets zero at atmospheric pressure. Gauge pressure is the pressure measured relative to atmospheric pressure, so when the pressure is equal to atmospheric pressure, the gauge pressure is zero. This is because gauge pressure is a measure of the pressure above or below atmospheric pressure, so when they are equal, there is no difference and the gauge pressure is zero.

A U-tube manometer is the most common measurement scale for a manometer because it is a simple and effective device for measuring pressure. It consists of a U-shaped tube partially filled with a liquid, such as mercury or water. When pressure is applied to one end of the tube, the liquid level in that arm will rise, while the level in the other arm will decrease. The difference in the liquid levels can be measured and used to determine the pressure. This design is widely used due to its simplicity, accuracy, and versatility in measuring both positive and negative pressures.

To convert inches Hg to inches H2O, we use the conversion factor of 2.04. Therefore, we multiply the given value of 24.2 inches Hg by 2.04 to get the equivalent value in inches H2O. The result is 328.60 inches H2O.

The conversion chart provided states that to convert inches Hg to psig, you need to multiply the height of liquid by 2.04. Therefore, to convert 100 inches H2O to inches Hg, you would multiply 100 by 2.04, which equals 204. The correct answer is 204.

A hepometer is not a common instrument for sensing pressure. Therefore, the correct answer is False.

Specific gravity is a measure of the density of a substance relative to the density of water. It is a dimensionless quantity, meaning it has no units. The specific gravity of a substance indicates how many times denser or lighter it is compared to water. A specific gravity greater than 1 means the substance is denser than water, while a specific gravity less than 1 means it is less dense. This measurement is commonly used in various industries, such as chemistry and engineering, to compare the densities of different substances and determine their buoyancy or solubility in water.

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In a strain gauge transducer, current flows through the wires, and the resistance changes proportionally to the stress or strain applied. This means that as the stress or strain increases, the resistance of the strain gauge also increases. By measuring the change in resistance, the applied stress or strain can be determined. Therefore, the correct answer is current.

A manometer is a device used to measure pressure, particularly in fluid systems. The most common measurement scale for a manometer is inches of mercury. This scale is commonly used because it provides an accurate and precise measurement of pressure. The height of the mercury column in the manometer indicates the pressure being measured. Other measurement scales like bars, PSIA, and inches of water are also used in certain applications, but inches of mercury is the most commonly used scale for manometers.

To convert inches H2O to inches Hg, we use the conversion factor of 2.04. Therefore, we multiply the given value of 300 inches H2O by 2.04 to get the equivalent value in inches Hg. So, 300 inches H2O multiplied by 2.04 equals 612 inches Hg. Hence, the correct answer is 22.09.

PSIA stands for "pounds per square inch absolute". This unit of pressure is used to measure the absolute pressure, which includes both the atmospheric pressure and the pressure exerted by the system being measured. It is important to specify "absolute" when using this unit to differentiate it from other pressure measurements that may only consider the pressure relative to atmospheric pressure.

The number of molecules per unit of volume defines density. Density is a measure of how much mass is contained in a given volume. In the case of gases and vapors, the density is determined by the number of molecules present in a specific volume.

The correct answer is "inches of mercury." This unit of measurement is commonly used to measure the level of mercury in a column. It represents the height of a column of mercury in inches, indicating the pressure exerted by the mercury. This measurement is often used in barometers and other devices to measure atmospheric pressure.

When molecules begin to move faster, the pressure increases. This is because the pressure exerted by a gas is directly proportional to the average kinetic energy of its molecules. When molecules move faster, their average kinetic energy increases, leading to more frequent and forceful collisions with the walls of the container. These collisions result in an increase in pressure.

The measurement of pressure equal to 0.987 atmospheres can be expressed in bars. In the International System of Units (SI), the bar is a unit of pressure equal to 100,000 pascals (Pa). It is commonly used in many fields, including physics, engineering, and meteorology, as a convenient unit for measuring pressure.

A capacitance transducer is a device that contains a measurement diaphragm and capacitor plates. It works by measuring the change in capacitance between the plates when pressure is applied to the diaphragm. As the pressure changes, the distance between the plates also changes, resulting in a change in capacitance. This change in capacitance can be measured and used to determine the pressure being applied. Therefore, a capacitance transducer is the correct answer because it fits the description of a device that contains a measurement diaphragm and capacitor plates.

At sea level, atmospheric pressure is equal to 0 PSIG. This is because PSIG stands for pounds per square inch gauge, which measures pressure relative to atmospheric pressure. At sea level, the atmospheric pressure is considered as the reference point, so the gauge pressure is 0.

An inch of water is a small unit of pressure measurement commonly used for low-pressure systems. It is defined as the pressure exerted by a column of water that is one inch in height. In this case, the given pressure of 0.036 psi at 4 degrees Celsius can be converted to inches of water using conversion factors.

The most common measurement scale used for vacuum is Inches of Mercury. This scale measures the pressure difference between the atmospheric pressure and the pressure in a vacuum. It is commonly used in industries such as aviation, automotive, and manufacturing. The term "inches of mercury" refers to the height of a column of mercury that would be supported by the pressure difference. This scale is widely recognized and used due to its accuracy and compatibility with various vacuum systems.