Manometer Questions

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Very Short Answers Questions [1 Mark Questions]

Ques. In a U-tube manometer, one end is open to the atmosphere, and the other end is attached to a pressurized gas of gauge pressure 40 kPa. The height of the fluid column on the atmospheric side is 60 cm, and that on the gas side is 30 cm. The manometer fluid used is

1. Oil
2. Liquid ammonia
3. Mercury
4. Water

Ans. The correct answer is c. Mercury

Explanation: Given

• Gauge pressure, P = 40 kPa = 40000 Pa
• Height different, h = 60 - 30 = 30 cm = 0.3 m

Gauge pressure, P = ⍴gh

⇒ density, ρ = P/gh

⇒ ρ = 40000/(9.8 x 0.3) = 13605 kg/m³

The density of mercury is approx 13605 kg/m³. Hence the fluid used is mercury.

Ques. A manometric liquid should suitably have

1. High density and low Vapour pressure
2. Low density and low Vapour pressure
3. High density and high Vapour pressure
4. Low density and high Vapour pressure

Ans. The correct answer is a. High density and low Vapour pressure

Explanation: A high density is desirable since it reduces the height of the column required for the manometer. A liquid with a high vapor pressure is less sensitive to pressure fluctuations, which may result in a slower increase of the manometric fluid. As a result, a fluid with a low vapor pressure is preferable.

Ques. A simple U-tube manometer can measure negative gauge pressures.

1. True
2. False

Ans. The correct answer is a. True

Explanation: If there is a positive gauge pressure, the height of the manometric fluid in a U-tube manometer in the test column will fall. If the gauge pressure is negative, the height will rise. A U-tube manometer can be utilized to measure negative gauge pressures. The negative pressure, however, cannot drop below -1 Bar.

Ques. In a stationary fluid, how does the local pressure of the fluid vary?

1. In the horizontal direction only
2. With depth only
3. Neither with depth nor along the horizontal direction
4. Both with depth and along the horizontal direction

Ans. The correct answer is b. With depth only

Explanation: The local pressure of a fluid is the same in all directions, according to Pascal's law. Therefore, the pressure will remain constant in the x and y directions. The extra weight of the water column above that point causes the local pressure to increase as depth increases.

Ques. Both ends of a U-tube manometer are exposed to the atmosphere. There exists a possibility that the height difference of the manometer is non-zero.

1. True
2. False

Ans. The correct answer is a. True

Explanation: When two immiscible fluids are used in the same manometer, the height difference may be non-zero. Even if the pressure on both surfaces is the same, the height will be different because the fluid with a higher density will be at a lower height.

Ques. Which of the following cannot be the value of the absolute pressure of a fluid at any point?

1. 1.013 bar
2. -1 bar
3. 0
4. 200 bar

Ans. The correct answer is b. -1 bar

Explanation: Absolute zero pressure is the standard against which absolute pressure is measured. Theoretically, absolute zero pressure is possible. Therefore, 0, and positive values are possible, but negative values are not.

Ques. Which state of matter a manometer cannot measure?

1. Fluid
2. Solid
3. Gas
4. Liquid

Ans. The correct answer is b. Solid

Explanation: A manometer is used to measure the pressure of fluids, so it cannot measure the state of matter of solids.

Ques. Which is the instrument used to measure blood pressure?

1. Enlarged Leg Manometer
2. Well Type Manometer
3. Sphygmomanometer
4. Inclined Tube Manometer

Ans. The correct answer is c. Sphygmomanometer

Explanation: The instrument used to measure blood pressure is called a sphygmomanometer.

Ques. The reference liquid in a U-tube manometer is

1. Mercury
2. Phenol
3. Petrol
4. Water

Ans. The correct answer is a. Mercury

Explanation: Mercury is commonly used as the reference liquid in U-tube manometers. It has a high density, which allows for a more compact manometer design.

Ques. Atmospheric pressure is measured using a device called

1. Ammeter
2. Barometer
3. Voltameter
4. Micrometer

Ans. The correct answer is b. Barometer

Explanation: The device used to measure atmospheric pressure is called a barometer.

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Short Answers Questions [2 Marks Questions]

Ques. What is a manometer?

Ans. A manometer is used to measure fluid pressure with respect to an outside source, which is usually considered to be the Earth's atmosphere.

Ques. What is the working principle of a manometer?

Ans. Manometers work on the principle that the pressure produced by a fluid in a column is proportional to its height. The most common manometer, known as the U-tube manometer, is made out of a U-shaped glass tube that is partially filled with a liquid, commonly mercury or water.

Ques. What are the errors in the manometer?

Ans. The error in the manometer is caused by the meniscus. The meniscus is the curved surface of a liquid at the interface between the liquid and air. It is caused by the attraction of the liquid molecules to the sidewalls of the container. The meniscus can be concave or convex, depending on the type of liquid and the surface it is in contact with.

Ques. What is pressure?

Ans. The force applied perpendicular to the surface of an object per unit area across which that force distributes is defined as pressure. The pressure in the surrounding environment is referred to as gauge pressure.

Ques. What is meant by 1 bar of pressure?

Ans. The bar is a metric pressure unit equal to 100,000 Pa (100 kPa). A pressure of one bar is somewhat lower than the Earth's current average atmospheric pressure at sea level (approximately 1.013 bar). 1 bar is approximately the air pressure on Earth at a height of 111 meters at 15 degrees Celsius, according to the barometric formula.

Ques. What is the difference between absolute and differential pressure?

Ans. Absolute pressure is the pressure measured relative to a perfect vacuum. It is the sum of all the pressures acting on a surface, including atmospheric pressure. 

Differential pressure is the difference in pressure between two points. It is used to measure the pressure drop across a device or the pressure difference between two fluids.

Ques. What is atmospheric pressure?

Ans. The pressure within atmos of the Earth is known as atmospheric pressure and is also referred to as air pressure or barometric pressure.

Ques. What is a barometer?

Ans. A barometer is a scientific instrument that measures air pressure in a particular region. Short-term weather changes can be predicted by variations in air pressure.

Ques. What are fluids?

Ans. Fluids are non-fixed-shape substances that flow easily due to larger intermolecular gaps. Fluids include both liquids and gases.

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Long Answers Questions [3 Marks Questions]

Ques. What are the advantages of manometers?

Ans. The following are the advantages of manometers

• Accuracy in Pressure Measurement: Manometers provide precise pressure readings, making them ideal for applications requiring precision control and monitoring.
• Versatility and Wide Range of Applications: Because of the ability to measure a wide range of pressures, from low vacuum to high pressure, manometers can be used in a variety of industries and sectors.
• Cost-Effectiveness: Manometers are less expensive than other pressure-measuring equipment while maintaining accuracy and dependability.

Ques. What are the disadvantages of manometers?

Ans. The following are the disadvantages of manometers

• They may break during transportation.
• When some manometric fluids are exposed to air, they can cause hazards.
• If the diameter of the tube is too small, an error occurs.
• Leveling is required.
• It is large in size and bulky.
• They have a smaller operating range which is on the order 1000 KN/meter-square.
• The manometer has a poor dynamic response.
• It has a slow response which makes it unsuitable for measuring fluctuating pressures 

Ques. What are the applications of manometers?

Ans. The following are the applications of manometers

• Industrial Applications: Manometers are used widely in sectors including manufacturing, chemical processing, and oil and gas, where accurate pressure management is essential to operational efficiency and safety.
• HVAC Systems: In heating, ventilation, and air conditioning (HVAC) systems, manometers are used to measure and balance air pressure in ducts, assuring optimal performance and air quality.
• Medical Applications: Manometers are used to monitor and manage pressure in medical devices such as ventilators and anesthesia machines, assuring patient safety and successful treatment.

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Very Long Answers Questions [5 Marks Questions]

Ques. What is the difference between a manometer and a barometer?

Ans. The following are the differences between a manometer and a barometer

Ques. A manometer tube contains a liquid of density 3 x 10³ kg/m³. When connected to a vessel containing a gas, the liquid level in the other arm of the tube is higher by 10 cm. When connected to another sample of enclosed gas, the liquid level in the arm of the manometer tube falls 7 cm below the liquid level in the first arm. Which of the two samples exerts more pressure and by what amount?

Ans. Given the density of the fluid, ρ = 3 x 10³ kg/m³

Case 1: When the liquid level in the other arm of the tube is higher by 10 cm.

h = 10 cm = 0.1 m

Pressure at the other arm, P1 = Pa + ρgh

Where Pa is the atmospheric pressure.

⇒ P₁ = 1.013 x 10⁵ + (3 x 10³ x 9.8 x 0.1)

⇒ P₁ = 1.0424 x 10⁵ Pa

Case 2: When the liquid in the other arm falls by 7 cm below the liquid level in the first arm

h = 7 cm = 0.07 m

Pressure at the other arm, P₂ = Pa - ρgh

⇒ P₂ = 1.013 x 10⁵ - (3 x 10³ x 9.8 x 0.07)

⇒ P₂ = 0.992 x 10⁵ Pa

Since P₁ > P₂, therefore the first sample will exert more pressure.

Ques. What are the different types of manometers?

Ans. The following are the different types of manometers

• U-Tube Manometer: This is the most basic and widely used kind of manometer. It is made up of a U-shaped tube that is partially filled with liquid. The height difference of the liquid column is determined by the pressure difference between the two arms of the tube, allowing pressure measurement.
• Inclined Manometer: Inclined manometers use an inclined tube rather than a U-shaped tube. The sensitivity of the manometer is affected by the angle of inclination, allowing for more exact pressure readings in particular applications.
• Bourdon Tube Manometer: Bourdon tube manometers use a flattened metal tube curved into a C shape. When pressure is applied, the tube straightens, and the movement is converted into a pressure reading.
• Digital Manometer: Digital manometers are becoming increasingly popular because they are easy to use and accurate. Pressure readings are displayed digitally on these manometers, removing the need for visual interpretation.

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