Pressure Questions

The concept of pressure comes into play when we talk about force area and the application of this force perpendicularly to a particular surface area. Have you ever thought about why the nails we use are manufactured with sharp ends or why the knives need to be so sharp?

The answer to all these questions is pressure force, which is defined as the force per unit area or the ratio of the force applied to the surface area over which the force is applied.

Hence, we can define pressure as:

The force applied per unit area, perpendicular to the surface of an object over which that force is dispersed or distributed is known as pressure.

Formula:

When a force of ‘F’ in Newton is perpendicularly applied to a surface area ‘A’, the pressure exerted on the surface by force is equal to F to A. Therefore, the formula for pressure (P) is:

P = F / A

Units of Pressure

Pascal (Pa), th SI unit of pressure.

The force of one newton applied over a surface area of a one-metre square is known as 1 pascal.

Types of Pressure

• Absolute pressure
• Gauge pressure
• Differential pressure
• Sealed pressure or vacuum pressure

Important Questions on Pressure

1) What happens to the pressure, when the area decreases?

a) Pressure decreases

b) Pressure increases

c) No change in pressure

d) Pressure remains constant

Correct Option: (b)

Explanation: Since, Pressure (P) = Force (F)/Area (A)

Hence, we can conclude from the above equation that pressure is inversely proportional to area. So, if the area decreases, the pressure increases.

2) The decrease in pressure takes place when _____>

a) The force is increased but not the area

b) The area is decreased but not the force

c) Either force increases or area decreases

d) The area increases and the force decreases

Correct Option: (d)

Explanation: Since, Pressure (P) = Force (F)/Area (A)

Therefore, we can conclude from the above equation that the pressure is directly proportional to the applied force and inversely proportional to the area.

Hence, if the area is increased and/or force is decreased, the pressure will decrease.

3) What will be the relation between F and F’ if a force F is acted upon a uniform rod of cross-section A and a force F’ is acted upon a uniform rod of cross-section 4A, and the pressure on both the rods is the same?

a) F/F’ = 1/4

b) F/F’ = 4

c) F’/F = 1/4

d) F/F’ = 1/16

Correct Option: (a)

Explanation: Pressure (P) = F/A (on first rod)

Pressure (P’) = F’/4A (on second rod)

Given;

P = P’

F/A = F’/4A

F/F’ = 1/4.

4) Find the ratio of pressure on the first cube (P) to the pressure on the second cube (P’). If some force is applied on the first cube of side 4m, and another force is applied on a cube of 2m, and the magnitude of this force is double than that of the previous force.

a) 1/10

b) 1/8

c) 1/20

d) 1/12

Correct Option: (b)

Explanation: P = F/4²

P = F/16

P’ = 2F/2²

P’ = F/2

P/P’ = (F/16)/(F/2)

= 1/8.

5) Pascal’s Law is valid only for _____.

a) Metals

b) Water

c) Solids

d) Fluids

Correct Option: (d)

Explanation: For water, gases and even other liquids, Pascal’s Law is valid. But, for any other form of matter, it is not applicable. Hence, Pascal’s Law is valid only for fluids; this can be concluded from the earlier fact.

6) Which among the following statements is stated in Pascal’s Law?

a) For every action, there exists an equal and opposite reaction.

b) The pressure for an ideal gas having constant volume and mass is directly proportional to temperature.

c) A change in pressure at any point in the fluid is transmitted so that the same change occurs everywhere throughout the fluid.

d) None of these.

Correct Option: (c)

Explanation: Pascal’s Law says that – A change in pressure at any point in the fluid is transmitted so that the same change occurs everywhere throughout the fluid.

7) The working of hydraulic machines is based on which of the following laws?

a) Ideal gas law

b) Newton’s law of cooling

c) Universal law of gravitation

d) Pascal’s law

Correct Option: (d)

Explanation: Pascal’s Law says that – A change in pressure at any point in the fluid is transmitted in such a way that the same change occurs everywhere throughout the fluid. This phenomenon is widely used in hydraulic machines by changing cross-sectional areas at required places.

8) What is the SI unit of pressure?

a) Kelvin

b) Candela

c) Pascal

d) Joule

Correct Option: (c)

Explanation: “Pascal” denoted by “Pa” is the SI unit of pressure, which is named after the famous scientist Blaise Pascal.

1 Pa = 1 N/m²

9) Name the instrument that is used to measure pressure.

a) Voltmeter

b) Odometer

c) Barometer

d) Ammeter

Correct Option: (c)

Explanation: To measure air pressure, a scientific instrument named “barometer” is used. Since pressure varies with altitude, a barometer can also be used to measure the altitude of a region.

10) A nail is always manufactured with one end pointed to confirm that for a given amount of force applied to it. True or False?

a) True

b) False

Correct Option: (a)

Explanation: The force per unit area is known as pressure. And to drive the nail easily into the wall, we need more pressure. So, a nail must be manufactured with one end pointed so that the pressure applied on it could be more.

Pressure Questions

1) Define pressure.

2) Define 1 pascal.

3) What are the different types of pressure?

4) What are the factors that affect pressure?

5) What is absolute pressure?

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