 # Constants in Physics  View Notes

Constants in Physics

The significance of constants in physics is that throughout all of the formulations of the basic theories of physics and the application to the real world, physical constants appear as fundamental invariant quantities, and they have specific and universally used symbols, that are of such importance that they must be known to as high an accuracy as is possible.

The physical constant also called the fundamental constant or the universal constant is a physical quantity that is believed to be universal in nature and has a constant value at all times.

Fundamental Constants in Physics

Speed of light in vacuum = c

Planck’s constant = h

The electric constant = ε0

The elementary charge = e

Constant Value in Physics

In physics, we deal with various dimensions, and to set the dimensions of an entity, the time length of an event, or the density of the fluid we need to compare them with other entities,  we use as a reference. These entities are the constants of physics, such as the speed of light (c), the charge of the electron(e) or mass (mp) of a proton, Rydberg constant, and so on.

For example, the value of Avogadro's number is 6.02214 x 10²³ mol⁻¹ remains the same everywhere.

Important Physical Constants

There are various fundamental constants to describe the universe as completely as possible; a few are listed below:

## Table: List of All Constants in Physics

 S.No Name Formula Value 1. Von Klitzing constant Rk = 2πh/e² 25812.80745...Ω 2. Curie constant C = X (T - Ө) 1.3047 K * A/(T * m) 3. Fine-structure constant α = e²/2hcε0 0.007297351 4. Compton wavelength λ = h/mc In meter: 2.42 x 10⁻¹²m In Angstrom = 0.242 Å 5. Impedance of free space Z0 = 1/ε0c0 376.730...Ω 6. Bohr radius a0  = 4πε0 h²/e²mₑ 0.0529 m 7. Faraday constant F = eNA 96,485 C/mol 8. Vacuum electric permittivity ε0 = 1/μ0c² 8.854 x 10⁻¹² F.m 9. Stefan–Boltzmann constant σ = π²k⁴/60h³c² 5.67 x 10⁻⁸Js⁻¹m⁻²K⁻⁴ 10. Thomson cross section σe = (8π/3)re² 6.6524587321 x 10⁻²⁹ m² 11. Vacuum magnetic permeability μ0 1.25663706212(19)x10⁻⁶N. A⁻²

All physics constants

## Table: All Constant Values in Physics

 S.No. Name Symbol Formula Value 1. Reduced Planck constant ħ h/2π 1.05457 x 10⁻³⁴ J.s 2. Deuteron mass mD -- 2.013553212745(40) u1875.612928(12)MeV1.67377 x 10⁻²⁷ kg or 1.67377 x 10⁻²⁴g 3. Josephson constant KJ 2e/h 483597.84... x 10⁸ Hz./V 4. Rydberg constant R∞ α2. mec/2h 10.973731.56(12)m⁻¹ 5. Proton mass mp -- 1.672621898(21) x 10⁻²⁷ kg1.672621898(21) x 10⁻²⁴ kg1.007276466879(91)u938.2720813(58) MeV/c² 6. Neutron mass mn -- 1.674927471(21) x 10⁻²⁷ kg1.674927471(21) x 10⁻²⁴ g1.00866491588(49) u939.5654133(58) MeV/c² 7. Electron mass me -- 9.10938356(11) x 10⁻³¹ kg9.10938356(11) x 10⁻²⁸ g5.48579909070(16) amu0.5109989461(31)MeV/c² 8. Boltzmann’s constant Kb 1.380649 x 10⁻²³ J/K1.380649 x 10⁻¹⁶ erg/K 9. Rest mass of the electron me 2R∞h/cα2 0.51099895000(15) Mev 11. Gas constant R -- 8.3144598(48) J/K mol8.3144598(48) x 10³ amu.m²/s²K8.3144598(48) x 10⁻² L.bar/K mol8.3144598(48) m³ .Pa/K.mol62.363577(36) L.T or/K.mol1.9872036(11) x 10⁻³ Kcal/K.mol8.2057338(47)x10⁻⁵m³.atm/K.mol0.082057338(47) L.atm/K.mol 12. Alpha particle mass mα -- 6.644657230(82) x ⁻²⁷ kg4.001506179127(63) u3.727379378(23) GeV/c²

Famous Constants in Physics

There are so many constants besides those I mentioned above, but some constants in physics are recognized widely.

Constant values in physics that are most popular among all the physical constants are as follows:

 S.No. Name Symbol Value 1. Speed of the light in vacuum c 3 x 10⁸ m/s 2. Planck’s constant h 6.62607015 x 10⁻³⁴ J.s 3. Gravitational constant G 6.673 x 10⁻¹¹ Nm²/kg² 4. Elementary charge e, qe (charge of a proton) 1.602176634 x 10⁻¹⁹ C 5. Electric constant ε0 8.9875517923(14) x 10⁹ kg.m³.s⁻⁴.A⁻²

Q1: Is MU a Physical Constant?

Ans: Yes, MU is a physical quantity. It is pronounced as mu naught or mu zero and symbolized as μ₀. The μ₀ is commonly called the permeability of free space, vacuum permeability, the permeability of vacuum, or the magnetic constant. Its value is,

μ₀ = 4π x 10⁻⁷ H/m ≈ 12.57 x 10⁻⁷ H/m

Q2:  Are Constants Dimensionless?

Ans: The dimensionless physical constants are the pure numbers because they don’t have any units attached to them, and they are independent of whatever system of units used.

For example, the formula for the specific gravity is defined as the density of the substance divided by the density of water at 4 ⁰C. Therefore, the units of density cancel out each other, and the term specific gravity becomes a dimensionless quantity.

Q3: What are the Physical Quantities? Give Some Examples.

Ans: The quantities in physics that are measurable are called physical quantities.

Such quantities are force, mass, velocity, light intensity, and many more.

Q4: What are the Two Types of Physical Quantities?

Ans: The two types of physical quantities are:

1. Fundamental or basics quantities, and

2. Derived quantities.

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