Pressure: Formula, Units, Difference, Factors Affecting Pressure and Solved questions

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Pressure can be referred to as the ratio between the normal force and area. Though we can say that force and area are both vector quantities, pressure is known as a scalar quantity and doesn't have any direction. Pressure can be termed as a method to explain force at a particular place of a continuous system.

Table of Content

Definition of Pressure
Units of Pressure
Difference between Stress and Pressure
Factors Affecting Pressure
Things to Remember
Sample Questions

Key Terms: Pressure, Unit of pressure, Normal force, Force, Scalar quantity

Definition of Pressure

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In Physics, Pressure is defined as the force applied perpendicular to the surface of an object per unit area over which that force is distributed.

In other words, pressure can be simply defined as the force that can be applied on per unit area of an object.

Pressure: Formula

Consider that the force (F) is applied to the area (A) perpendicular on the surface of an object, then the pressure exerted is equal to the ratio of F and A.

Pressure, P = F/A

where, F = force applied in Newton

A = Area of the object in sq.m.

P = Pressure

Pressure: Dimensional Formula

The dimensional equation is the representation of fundamental qualities in the basic dimension form is represented in the form of M, L, and T. Where M stands for mass, L stands for length and T stands for time.

The dimensional equation of pressure is represented as M¹ L^-1 T^-2

Read More: Stress and Strain

Units of Pressure

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The pressure can be expressed in various measuring units, Three of the most popularly used units are: SI, CGS and MKS units.

SI Unit:

The pressure is defined as the force of one Newton is applied to the one-meter square area of an object.

In the SI system, the unit of force is Newton, and the unit of area is sq.m. Then the unit of pressure will be N/m². It is known as Pascal and represented by Pa.

SI unit of pressure is Pascal (Pa)
Pa = N/m² = kg/m*s²

The Pascal is a small unit of pressure. The pressure is mostly given in KiloPascal (KPa) which means 1000 Pascals. Another commonly used unit of pressure is atmospheric pressure (atm). The standard atm is 1 atm and it is equal to 10kPa.

CGS Unit :

The tens CGS is an abbreviation for centimeter-gram-second. The CGS unit of pressure is Barye (Ba) which is equal to 1 dyne per sq. cm.

1 Barye (Ba) = 0.1 Pascal (Pa)

MKS Unit:

The MKS stands for meter-kilo-second. The MKS unit of pressure is also Pascal.

Other than these units, there are several other units of pressure namely Pounds Per Square Inch (Ibf/in²), Bar (bar), Atmospheric Pressure (atm), Centimeters of Water, mm or inches of mercury (used as a unit of blood pressure), MSW, FSW, and Torr (torr).

Units of Pressure

The pressure can be calculated for solid as well as fluids (liquids and gases). The object submerged in the water experiences the pressure exerted above the water level and also in the case of gases the molecules of gases get more accelerated due to high pressure and the volume of gas becomes less.

Read Also: Reynolds Number

Difference between Stress and Pressure

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Pressure and stress are the two confusing terms for many students but the right understanding of the concepts can make clear that these are both different. Mathematically they are the same but in actuality, these are two different terms.

Pressure refers to the force applied on the unit area of the surface of an object while stress is the internal resisting force applied to the deformation per unit area. Stress is a material property. Given below is the table which gives a thorough understanding of the difference between stress and pressure on various parameters.

S.No.	Stress	Pressure
1.	Stress is defined as the internal resistive force to deformation per unit area.	Pressure is the force exerted on the unit area of cross-section on the surface of the object.
2.	Stress cannot be measured.	Pressure can be measured by pressure measuring devices.
3.	Stress develops internally.	The pressure exerts externally.
4.	Stress may be of many types i.e. tensile, compressive and shear.	The pressure is always compressive.
5.	Stress can be developed by both positive and negative forces.	Pressure is always a positive force.
6.	Stress is a material property i.e. it acts only on solid objects.	The pressure occurs on all matters (solid, liquid, gases).

Read More: Bulk Modulus

Pressure: Factors Affecting It

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As per the formula of pressure it can be affected by mainly two factors i.e. force and the area over which the force is applied. If the force increases and the pressure also increase the area remains the same and vice versa.

In case of liquid pressure, it is affected by three factors namely density of the liquid, depth of liquid or height of the liquid column, and acceleration due to gravity on liquid. It can be understood by the formula of liquid pressure P = hdg.

The pressure of gas is affected by the temperature and volume of the gas. Due to an increase in temperature, the molecules of the gas move with high velocity and it transfers heat to other molecules by collision, as a result, the pressure of gas increases. If the volume of the gas container decreases the kinetic energy of gas molecules increases and it strikes on all of the containers increasing the pressure of the gas.

Read More: Young's Modulus

Points to Remember

Pressure is referred to as the scalar quantity which is measured in force per unit area and is perpendicular to the surface to which it is applied.
Pressure exists due to the presence of gravity and the motion of the particles.
Pressure is denoted as P=F/A
There are four types of pressure which include, gauge pressure, absolute pressure, differential pressure, and vacuum pressure.
Pressure is present in solids, liquids as well as gases.

Sample Questions

Que.1 The pressure is which type of quantity scalar or vector? (1 mark)

Ans- As we know pressure is a ratio of force per unit area so it is a scalar quantity.

Que.2 What is the nature of pressure force? (1 mark)

Ans-As we talk about the pressure it is always compressive. But the stress can be tensile, compressive, and shear.

Que.3 Give the SI unit of pressure? (1 mark)
a. Bar
b. Torr
c. Pascal
d. N/mm²

Ans- (c) The SI unit of pressure is Pascal (Pa).

Que.4 Define atmospheric pressure? (1 mark)

Ans- The weight of the air column acting per unit area is known as atmospheric pressure. The standard atmospheric pressure is equivalent to 760 mm of mercury column.

Que.5 Convert 5 Barye into Pascal? (1 mark)

Ans- We know that, 1 Barye = 0.1 Pascal

5 Barye = 5/10 Pa = 0.5 Pa

Que.6 Is pressure can be experienced for all matters i.e. solids, liquids, and gases? (1 mark)

Ans- Yes, the pressure is applied on all the matters solids, liquids, gases. While the stress can be experienced only in solid objects. It is a material property.

Read More:

Elastic Limit	Mechanical Properties of Fluids	Viscosity
Surface Tension	Fluid Friction	Unit of Viscosity
Buoyant Force	Mechanical Properties of Solid	Poisson’s Ratio
Shearing Stress	Pascal’s Law	Hydraulic Machines
Surface Energy	Bernoulli’s principle	Venturi-meter

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If both the number of protons and the neutrons are conserved in each nuclear reaction, in what way is mass converted into energy (or vice versa) in a nuclear reaction? Explain.
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3.
Two thin lenses of focal length \( f_1 \) and \( f_2 \) are placed in contact with each other coaxially. Prove that the focal length \( f \) of the combination is given by \[ f = \frac{f_1 f_2}{f_1 + f_2}. \]
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Pressure: Formula, Units, Difference, Factors Affecting Pressure and Solved questions

Definition of Pressure

Pressure: Formula

Pressure: Dimensional Formula

Units of Pressure

Difference between Stress and Pressure

Pressure: Factors Affecting It

Points to Remember

Sample Questions

CBSE CLASS XII Related Questions

1.
If both the number of protons and the neutrons are conserved in each nuclear reaction, in what way is mass converted into energy (or vice versa) in a nuclear reaction? Explain.

2.
Suppose a pure Si crystal has \( 5 \times 10^{28} \) atoms per \( \text{m}^3 \). It is doped with \( 5 \times 10^{22} \) atoms per \( \text{m}^3 \) of Arsenic. Calculate majority and minority carrier concentration in the doped silicon. (Given: \( n_i = 1.5 \times 10^{16} \, \text{m}^{-3} \))

3.
Two thin lenses of focal length \( f_1 \) and \( f_2 \) are placed in contact with each other coaxially. Prove that the focal length \( f \) of the combination is given by \[ f = \frac{f_1 f_2}{f_1 + f_2}. \]

4.
The figure shows three point charges kept at the vertices of triangle ABC. The net electric field, due to this system of charges, at the midpoint M of base BC will be:

5.
Write the expression for the magnetic field due to a current element in vector form. Consider a 1 cm segment of a wire, centered at the origin, carrying a current of 10 A in positive x-direction. Calculate the magnetic field \( \mathbf{B} \) at a point \( (1 \, \text{m}, 1 \, \text{m}, 0) \).

6.
Photoemission of electrons occurs from a metal (\( \phi_0 = 1.96 \, \text{eV} \)) when light of frequency \( 6.4 \times 10^{14} \, \text{Hz} \) is incident on it. Calculate: Energy of a photon in the incident light, The maximum kinetic energy of the emitted electrons, and The stopping potential.

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Pressure: Formula, Units, Difference, Factors Affecting Pressure and Solved questions

Definition of Pressure

Pressure: Formula

Pressure: Dimensional Formula

Units of Pressure

Difference between Stress and Pressure

Pressure: Factors Affecting It

Points to Remember

Sample Questions

CBSE CLASS XII Related Questions

1. If both the number of protons and the neutrons are conserved in each nuclear reaction, in what way is mass converted into energy (or vice versa) in a nuclear reaction? Explain.

2.Suppose a pure Si crystal has \( 5 \times 10^{28} \) atoms per \( \text{m}^3 \). It is doped with \( 5 \times 10^{22} \) atoms per \( \text{m}^3 \) of Arsenic. Calculate majority and minority carrier concentration in the doped silicon. (Given: \( n_i = 1.5 \times 10^{16} \, \text{m}^{-3} \))

3.Two thin lenses of focal length \( f_1 \) and \( f_2 \) are placed in contact with each other coaxially. Prove that the focal length \( f \) of the combination is given by \[ f = \frac{f_1 f_2}{f_1 + f_2}. \]

4.The figure shows three point charges kept at the vertices of triangle ABC. The net electric field, due to this system of charges, at the midpoint M of base BC will be:

5.Write the expression for the magnetic field due to a current element in vector form. Consider a 1 cm segment of a wire, centered at the origin, carrying a current of 10 A in positive x-direction. Calculate the magnetic field \( \mathbf{B} \) at a point \( (1 \, \text{m}, 1 \, \text{m}, 0) \).

6.Photoemission of electrons occurs from a metal (\( \phi_0 = 1.96 \, \text{eV} \)) when light of frequency \( 6.4 \times 10^{14} \, \text{Hz} \) is incident on it. Calculate: Energy of a photon in the incident light, The maximum kinetic energy of the emitted electrons, and The stopping potential.

Comments

SUBSCRIBE TO OUR NEWS LETTER

1.
If both the number of protons and the neutrons are conserved in each nuclear reaction, in what way is mass converted into energy (or vice versa) in a nuclear reaction? Explain.

2.
Suppose a pure Si crystal has \( 5 \times 10^{28} \) atoms per \( \text{m}^3 \). It is doped with \( 5 \times 10^{22} \) atoms per \( \text{m}^3 \) of Arsenic. Calculate majority and minority carrier concentration in the doped silicon. (Given: \( n_i = 1.5 \times 10^{16} \, \text{m}^{-3} \))

3.
Two thin lenses of focal length \( f_1 \) and \( f_2 \) are placed in contact with each other coaxially. Prove that the focal length \( f \) of the combination is given by \[ f = \frac{f_1 f_2}{f_1 + f_2}. \]

4.
The figure shows three point charges kept at the vertices of triangle ABC. The net electric field, due to this system of charges, at the midpoint M of base BC will be:

5.
Write the expression for the magnetic field due to a current element in vector form. Consider a 1 cm segment of a wire, centered at the origin, carrying a current of 10 A in positive x-direction. Calculate the magnetic field \( \mathbf{B} \) at a point \( (1 \, \text{m}, 1 \, \text{m}, 0) \).

6.
Photoemission of electrons occurs from a metal (\( \phi_0 = 1.96 \, \text{eV} \)) when light of frequency \( 6.4 \times 10^{14} \, \text{Hz} \) is incident on it. Calculate: Energy of a photon in the incident light, The maximum kinetic energy of the emitted electrons, and The stopping potential.