All questions of Measurement of Pressure, pH & Viscosity for Electronics and Communication Engineering (ECE) Exam

From, Hagin-Poisuille equal to laminar flow

The main types of sensing elements are Bourdon tubes, diaphragms, capsules, and bellows. The Bourdon tube is a sealed tube that deflects in response to applied pressure.

According to Pascal’s law, the local pressure of a fluid is same in all directions. Hence, the pressure won’t vary along the x and y-direction. The local pressure will increase with an increase in depth due to the extra weight of water column above that point.

Solution:

Given:

Terminal velocity of ball in oil A, V1 = 0.01 m/s

Terminal velocity of ball in oil B, V2 = 0.002 m/s

Density of both oils is assumed to be equal.

Kinematic viscosity of oil A, ν1 = 5 x 10^-3 m^2/s

Kinematic viscosity of oil B, ν2 = ?

Terminal velocity of a ball falling through a fluid is given by the equation:

V = (2/9) * (g * r^2 * (ρ - σ) / η)

where

g = acceleration due to gravity

r = radius of the ball

ρ = density of the ball

σ = density of the fluid

η = dynamic viscosity of the fluid

From the given information, we can write:

For oil A:

V1 = (2/9) * (g * r^2 * (ρ - σ) / ν1)

For oil B:

V2 = (2/9) * (g * r^2 * (ρ - σ) / ν2)

Dividing both equations, we get:

V1/V2 = (ν2 / ν1)

ν2 = (V1 / V2) * ν1

Substituting the given values, we get:

ν2 = (0.01 / 0.002) * 5 x 10^-3

ν2 = 25 x 10^-3 m^2/s

Therefore, the kinematic viscosity of oil B is 25 x 10^-3 m^2/s.

Hence, the correct option is (c).

Capacitive pressure sensors measure pressure by detecting changes in electrical capacitance caused by the movement of a diaphragm.

Defective calibration is not a failure in pH meters. Failure occurs due to defective electrodes, defective input circuitry, and defective electronic circuitry.

Manganin wire is the most suitable measurement device for high-pressure liquids. It has high stability and durability on a long-term basis.

Absolute zero pressure is the reference used for the measurement of absolute pressure. Absolute zero pressure is possible (theoretically). Hence, 0 and positive values are possible, but a negative value is impossible.

The inclined manometer is essential for retaining the most accurate pressure levels for industrial gas applications. A low-pressure industrial gas system may be used to heat or cool manufacturing processes. A small blockage within the gas system can be detected with an inclined manometer and corrected.

The Bourdon tube is an almost rectangular or elliptical cross-section tube made from materials such as stainless steel or phosphor bronze.

The height of the manometric fluid in a U-tube manometer in the test column would fall if there is positive gauge pressure. The height would increase if there is negative gauge pressure. It is possible to measure negative gauge pressures with a U-tube manometer. However, the negative pressure cannot fall below -1 Bar.

The hydrogen ion concentration of pure water is 1×10⁷ moles/litre. It can be represented as [H+]=1×10⁷ moles/litre.

PH is defined as the negative logarithm of hydrogen ion concentration. Hence, its formula is -log₁₀[H+].

Understanding Manometers
Manometers are devices used to measure the pressure of fluids, and they can be applied to both gases and liquids.
Types of Fluids Measured
- Gases: Manometers are effectively used to measure the pressure of gases. They provide accurate readings by comparing the gas pressure to atmospheric pressure or to a vacuum.
- Liquids: Manometers can also measure the pressure of liquids. The height difference in a liquid column helps determine the pressure exerted by the liquid.
Why Option 'C' is Correct
- Versatility: The correct answer is option 'C' because manometers are versatile instruments capable of measuring both gas and liquid pressures. This capability is due to their design, which relies on the hydrostatic principles that apply to both types of fluids.
- Application in Various Industries: Manometers are widely used in various industries such as HVAC, chemical processing, and hydraulics, where both gases and liquids are present.
- Types of Manometers: There are various types of manometers, including U-tube manometers, digital manometers, and inclined manometers, which can be adapted for different fluid types.
Conclusion
In summary, manometers are essential tools for measuring pressures in both gases and liquids, making option 'C' the correct answer. Their design and operating principles allow them to function effectively across different fluid types, highlighting their importance in various applications.

Mechanical gauges are instruments that measure pressure, dimensions, levels, etc. They can be mechanical or electro-mechanical devices and offer displays ranging from direct-reading rules to digital LCDs. Gauges that measure pressure are classified as analog or digital depending on their readouts.

The Nernst equation is an equation used to calculate the potential difference (E) between two half-cells in an electrochemical cell. It relates the potential difference to the standard potential (Eo) of the cell, the gas constant (R), the temperature (T), the Faraday constant (F), and the concentration (C) of the species involved in the redox reaction.

The Nernst equation is given by the following statement:

E = Eo - (2.303 RT/F) log C

Explanation:

- The Nernst equation describes the relationship between the potential difference (E) and the concentration (C) of the species involved in the redox reaction.
- The equation includes the standard potential (Eo) of the cell, which is the potential difference when the concentrations of the species are 1 M and the pressure of the gases involved is 1 atm.
- The gas constant (R) is a constant that relates the temperature (T) to the energy of a system.
- The Faraday constant (F) is a constant that relates the charge of an electron to the number of moles of electrons in a mole of substance.
- The logarithm (log) in the equation is used to calculate the ratio of the concentrations of the species involved in the redox reaction.

In option 'A', the correct form of the Nernst equation is given:

E = Eo - (2.303 RT/F) log C

- The equation includes the standard potential (Eo), which is subtracted from the term (2.303 RT/F) log C.
- The logarithm (log) is used to calculate the ratio of the concentration (C) of the species involved in the redox reaction.
- This equation allows us to calculate the potential difference (E) between two half-cells based on the concentration of the species involved in the redox reaction.

Therefore, option 'A' is the correct answer as it correctly represents the Nernst equation.

The orifice type device is used for measurement of viscosity in which viscosity is converted to pressure change.

The options may tempt you to subtract the readings, but the concept of barometer and manometer is important. Barometer measures the atmospheric pressure whereas, the manometer reads the gauge pressure. Hence, we need to add the two values.

Internal Resistance of pH Electrodes
Internal resistance is an important factor to consider when using pH electrodes for measurement. pH electrodes have a very high internal resistance due to the unique composition of the reference and glass electrodes.

Reasons for High Internal Resistance
- The reference electrode is typically made of a silver/silver chloride wire immersed in a potassium chloride solution. This composition results in a high resistance.
- The glass electrode, which measures the pH of the solution, is made of a special glass membrane that is highly resistant to electrical flow.

Effects of High Internal Resistance
- The high internal resistance of pH electrodes can lead to slower response times and potential inaccuracies in pH measurements.
- It is important to properly condition and calibrate pH electrodes to ensure accurate readings despite the high internal resistance.

Conclusion
In conclusion, pH electrodes have a very high internal resistance due to the composition of the reference and glass electrodes. Understanding and accounting for this high resistance is crucial for accurate pH measurements.

Pressure measuring devices using liquid columns in vertical or inclined tubes are called manometers. One of the most common is the water-filled u-tube manometer used to measure pressure difference in pitot or orifices located in the airflow in air handling or ventilation system.

Rearranging Poiseuille’s equation we get

Null-detector type pH meter

The null-detector type pH meter is the simplest type of pH meter among the options given. It is a basic and straightforward device used for measuring the pH of a solution.

Working Principle
The null-detector type pH meter works on the principle of null detection. It consists of a pH electrode, a reference electrode, and a potentiometer. The pH electrode is immersed in the solution whose pH is to be measured, while the reference electrode is immersed in a reference solution. The potentiometer compares the potential difference between the two electrodes and adjusts the voltage until a null point is reached.

Measurement Process
1. Calibration: Before taking measurements, the pH meter needs to be calibrated using standard buffer solutions with known pH values. This ensures accurate and reliable readings.
2. Measurement: Once calibrated, the pH meter is ready for use. The pH electrode is immersed in the solution, and the potentiometer is adjusted until the voltage difference between the pH electrode and reference electrode is zero. At this null point, the pH value of the solution can be read directly from the potentiometer scale.

Advantages
- Simplicity: The null-detector type pH meter is simple in design and operation, making it easy to use even for beginners.
- Cost-effective: It is a cost-effective option compared to other types of pH meters.
- Reliability: With proper calibration, the null-detector type pH meter can provide accurate and reliable pH measurements.

Limitations
- Limited features: This type of pH meter does not have advanced features such as automatic temperature compensation or digital display.
- Manual adjustments: The null-detector type pH meter requires manual adjustments to reach the null point, which may be time-consuming and less precise compared to modern digital pH meters.

In conclusion, the null-detector type pH meter is the simplest among the given options. It operates on the principle of null detection and provides basic pH measurements. While it may lack advanced features, it is a cost-effective and reliable choice for simple pH measurements.

The Bourdon-tube gauge, invented about 1850, is still one of the most widely used instruments for measuring the pressure of liquids and gases of all kinds, including steam, water, and air up to pressures of 100,000 pounds per square inch (70,000 newtons per square cm).

Dead weight gauge is used for the measurement of pressure of about 7000 bar. A dead weight tester is an instrument that calibrates pressure by determining the weight of force divided by the area the force is applied. The formula for dead weight testers is pressure equals force divided by the area where force is applied.

Characteristics of Chopper Amplifier pH Meters
Chopper amplifier pH meters are specialized devices used for measuring pH levels with high accuracy and stability. However, not all characteristics listed in the options accurately describe their functionality.
Understanding the Options
- Option A: Direct voltage from the electrodes is chopped at the main frequency.
This is a true characteristic as chopper amplifiers utilize chopping techniques to convert the slow varying DC signals into AC, which can be amplified effectively.
- Option B: Using choppers for high-input resistance gives rise to spikes of waveforms at the output.
This is also correct; the chopper mechanism can introduce transients or spikes in the output due to the rapid switching of signals.
- Option C: It leads to stability in DC output of a phase-sensitive rectifier.
This option is incorrect in the context of chopper amplifiers. While phase-sensitive rectifiers can enhance stability, the primary purpose of a chopper amplifier is to reduce drift and noise rather than inherently stabilize the DC output.
- Option D: Magnitude of surge increases in the glass electrode output.
This statement is accurate as the glass electrode output can indeed experience surges, particularly if the input impedance is high, leading to potential spikes.
Conclusion
In summary, Option C is the correct answer as it does not accurately characterize the chopper amplifier pH meter's functionality. The primary role of the chopper is noise reduction and signal enhancement, rather than ensuring stability in the DC output of a phase-sensitive rectifier. Understanding these principles is crucial for effectively using and interpreting pH measurements in various applications.

Piezometer is one of the simplest forms of manometers. It can be used for measuring moderate pressures of liquids. The setup of piezometer consists of a glass tube, inserted in the wall of a vessel or of a pipe. The tube extends vertically upward to such a height that liquid can freely rise in it without overflowing.

A high density is favourable because the height of the column required for the manometer would below. A liquid with high vapour pressure would be less sensitive to changes in pressure and may result in a slower rise of the manometric fluid. Thus, a fluid with low vapour pressure is favourable.

Diaphragms and Capsules:

Diaphragms are thin, flexible membranes that can vibrate to capture sound waves. On the other hand, capsules are the components of a microphone that contain the diaphragms. Let's discuss the relationship between diaphragms and capsules in microphones.

True:

Diaphragms are the main components of capsules:
- Capsules in microphones are typically made up of diaphragms. The diaphragm is the essential part of the capsule that converts sound waves into electrical signals.
- The diaphragm moves in response to sound waves, causing variations in the electrical signal that are then transmitted through the microphone.

Capsules are responsible for converting sound to electrical signals:
- The diaphragm within the capsule plays a crucial role in capturing sound and converting it into electrical signals.
- The design and quality of the diaphragm greatly impact the overall performance and sound quality of the microphone.

Conclusion:

In conclusion, capsules are indeed made from diaphragms in microphones. The diaphragm is a vital component within the capsule that captures sound waves and converts them into electrical signals. This relationship highlights the importance of diaphragms in the functioning of microphone capsules.

In an acidic solution, the value of hydrogen ion concentration is greater than that of hydroxyl ion concentration. It can be represented as [H+]>[OH-].

Relation between the concentration of hydrogen and hydroxyl ions in a basic solution:

In a basic solution, the concentration of hydroxyl ions (OH-) is greater than the concentration of hydrogen ions (H+). This can be explained by the concept of dissociation of water and the self-ionization of water.

1. Dissociation of water:
Water (H2O) can act as an acid and a base through a process called self-ionization. In this process, a small fraction of water molecules dissociate into hydrogen ions (H+) and hydroxyl ions (OH-).

H2O ⇌ H+ + OH-

The concentration of hydrogen ions and hydroxyl ions in pure water at 25°C is 1 × 10^-7 M each. This is because water dissociates into equal numbers of hydrogen and hydroxyl ions, resulting in a neutral solution.

2. Self-ionization of water:
In a basic solution, the concentration of hydroxyl ions is greater than the concentration of hydrogen ions. When an alkaline substance is added to water, it can increase the concentration of hydroxyl ions, leading to a basic solution.

For example, if sodium hydroxide (NaOH) is added to water, it dissociates into sodium ions (Na+) and hydroxyl ions (OH-). The hydroxyl ions contribute to the concentration of OH- in the solution, making it greater than the concentration of H+.

NaOH ⇌ Na+ + OH-

As a result, the concentration of hydroxyl ions is higher than the concentration of hydrogen ions in a basic solution.

Conclusion:
In summary, the correct answer is option B: The value of hydroxyl ion concentration is greater than the value of hydrogen ion concentration in a basic solution. This is because the addition of alkaline substances increases the concentration of hydroxyl ions, making the solution basic.

The displacement is measured using strain gauges, and the number of strain gauges required is four. This can be explained based on the working principle of strain gauges and the need for accurate displacement measurement.

1. Working Principle of Strain Gauges:
Strain gauges are devices that measure the strain or deformation of an object when subjected to external forces. They work on the principle that when an object undergoes deformation, its resistance changes proportionally. Strain gauges consist of a thin wire or foil that is attached to the surface of the object. As the object deforms, the wire or foil also deforms, leading to a change in resistance.

2. Measurement of Displacement using Strain Gauges:
To measure displacement using strain gauges, they are attached to the object in a specific arrangement. When the object undergoes displacement, the strain gauges experience strain, which causes a change in their resistance. By measuring this change in resistance, the displacement can be determined.

3. Bridge Configuration:
To obtain accurate displacement measurements, strain gauges are usually connected in a bridge configuration called a Wheatstone bridge. A Wheatstone bridge consists of four strain gauges connected in a specific arrangement. The strain gauges are arranged in two pairs, with each pair connected in a series and the two pairs connected in parallel.

4. Balancing the Bridge:
In the Wheatstone bridge configuration, the objective is to balance the bridge by adjusting the resistance of one of the strain gauges. This is done by applying a known reference voltage to the bridge and adjusting the resistance until the bridge is balanced. When the bridge is balanced, the output voltage is zero, indicating no displacement.

5. Measurement of Displacement:
When the object undergoes displacement, the strain gauges experience strain, causing a change in their resistance. This unbalances the Wheatstone bridge, resulting in a non-zero output voltage. By measuring this output voltage, the displacement can be determined.

6. Four Strain Gauges:
To accurately measure displacement using strain gauges, four strain gauges are required. The use of four strain gauges allows for better compensation of temperature effects, improves accuracy, and provides redundancy in case one of the strain gauges fails.

In conclusion, when measuring displacement using strain gauges, four strain gauges are normally required. This allows for accurate and reliable measurement by using a Wheatstone bridge configuration and compensating for temperature effects.

Mcleod Gauge works on the principle of Boyle's Law. Boyle's Law states that if the temperature and amount of gas remain unchanged, the absolute pressure exerted by a given mass of gas is inversely proportional to the volume it occupies.

According to Stoke’s theorem,

Both diaphragm and capsule convert pressure into displacement which can be measured using indicating instruments. Displacement will be proportional to applied pressure.

Pure water is known to be a weak electrolyte. To understand why, we first need to understand the concept of electrolytes and their behavior in water solutions.

Electrolytes are substances that, when dissolved in water, break apart into ions. These ions can conduct electricity, which is why solutions containing electrolytes are able to conduct electric current. There are two types of electrolytes: strong electrolytes and weak electrolytes.

Strong electrolytes completely dissociate into ions when dissolved in water, resulting in a high concentration of ions in the solution. Examples of strong electrolytes include strong acids (such as hydrochloric acid) and strong bases (such as sodium hydroxide). These substances exist almost entirely as ions in solution and conduct electricity very efficiently.

Weak electrolytes, on the other hand, only partially dissociate into ions when dissolved in water, resulting in a lower concentration of ions in the solution. Examples of weak electrolytes include weak acids (such as acetic acid) and weak bases (such as ammonia). These substances exist as a mixture of ions and uncharged molecules in solution and conduct electricity less efficiently compared to strong electrolytes.

Now, coming back to pure water, it is considered a weak electrolyte because it undergoes a process called self-ionization. In self-ionization, a small fraction of water molecules dissociate into ions:

H2O ⇌ H+ + OH-

In pure water, the concentration of H+ ions (also called hydronium ions) and OH- ions is very low, approximately 10^-7 mol/L each. This means that only a small fraction of water molecules are ionized at any given time. Consequently, pure water has a very low concentration of ions, making it a weak electrolyte.

It is worth noting that even though pure water is a weak electrolyte, it still conducts electricity to some extent. This is because the small concentration of ions present in pure water allows for the flow of electric current, although not as effectively as solutions containing strong electrolytes.

In summary, pure water is known to be a weak electrolyte due to its ability to undergo self-ionization and the resulting low concentration of ions in the solution.

Understanding Bourdon Tubes
Bourdon tubes are mechanical devices widely used in pressure measurement applications. They are designed to convert pressure into a readable displacement, making them essential in various engineering and industrial contexts.
How Bourdon Tubes Work
- Structure: A Bourdon tube is a curved, hollow tube that typically has an elliptical cross-section. When pressure is applied to the inside of the tube, it tends to straighten out.
- Displacement Mechanism: As the internal pressure increases, the deformation of the tube causes it to straighten, which is a measurable displacement. This movement can then be linked to a needle on a dial gauge, providing a visual representation of the pressure level.
Why Option A is Correct
- Pressure to Displacement: The primary conversion that occurs in a Bourdon tube is the transformation of pressure into a physical displacement. This is why option 'A' is the correct answer.
- Other Options:
- Pressure to Voltage: This conversion typically involves electronic sensors, not Bourdon tubes.
- Pressure to Strain: While strain may occur in the material, it is not the primary purpose of a Bourdon tube.
- Pressure to Force: Although pressure can be related to force, Bourdon tubes specifically translate pressure to a mechanical displacement for measurement.
Applications of Bourdon Tubes
- Widespread Use: Bourdon tubes are commonly found in pressure gauges for HVAC systems, automotive applications, and industrial machinery, providing reliable and accurate pressure readings.
- Advantages: They are robust, relatively inexpensive, and do not require external power, making them ideal for various applications.
In summary, Bourdon tubes efficiently convert pressure into displacement, facilitating accurate pressure measurement in numerous settings.

The disadvantages of chopper amplifier type pH meter can be overcome using a vibrating condenser. It is used in the place of the mechanical chopper.

Pressure measurement is the analysis of an applied force by a fluid, whether a liquid or a gas, on a surface. Pressure is basically measured in the units of force per unit of the surface. Instruments used to measure and display pressure in an integral unit are called pressure meters or pressure gauges or vacuum gauges.

Monometer - Visual indication of pressure level.

In bellows pressure to force conversion takes place, which is acted on bellows and can be measured for calculating applied pressure.

Water vs. Transformer Oil as a Manometric Liquid:
Water and transformer oil are commonly used as manometric liquids in pressure measurement applications. However, there are some key differences between the two when it comes to their suitability for specific pressure differentials.

Differences:
- Water is used for large pressure differentials: Water is commonly used as a manometric liquid for measuring large pressure differentials due to its low viscosity and high density. It provides accurate readings in situations where the pressure difference is significant.
- Transformer oil is used for large pressure differentials: Transformer oil, on the other hand, is typically used for measuring smaller pressure differentials. It has a higher viscosity compared to water, making it more suitable for applications where the pressure difference is not as great.
- Transformer oil has evaporation problems: One of the drawbacks of using transformer oil as a manometric liquid is its tendency to evaporate over time. This can lead to inaccuracies in pressure measurements, especially in long-term applications.
- Water has evaporation problems: Water, on the other hand, does not have significant evaporation issues compared to transformer oil. It remains stable over time, providing reliable and consistent pressure readings.
In conclusion, while both water and transformer oil can be used as manometric liquids, their suitability depends on the specific pressure differential requirements of the application. Water is preferred for large pressure differentials due to its stability and low evaporation rate, while transformer oil is more suitable for smaller pressure differentials despite its evaporation problems.