What is Constants: Definition and 486 Discussions

A physical constant, sometimes fundamental physical constant or universal constant, is a physical quantity that is generally believed to be both universal in nature and have constant value in time. It is contrasted with a mathematical constant, which has a fixed numerical value, but does not directly involve any physical measurement.
There are many physical constants in science, some of the most widely recognized being the speed of light in vacuum c, the gravitational constant G, the Planck constant h, the electric constant ε0, and the elementary charge e. Physical constants can take many dimensional forms: the speed of light signifies a maximum speed for any object and its dimension is length divided by time; while the fine-structure constant α, which characterizes the strength of the electromagnetic interaction, is dimensionless.
The term fundamental physical constant is sometimes used to refer to universal-but-dimensioned physical constants such as those mentioned above. Increasingly, however, physicists only use fundamental physical constant for dimensionless physical constants, such as the fine-structure constant α.
Physical constant, as discussed here, should not be confused with other quantities called "constants", which are assumed to be constant in a given context without being fundamental, such as the "time constant" characteristic of a given system, or material constants (e.g., Madelung constant, electrical resistivity, and heat capacity).
Since May 2019, all of the SI base units have been defined in terms of physical constants. As a result, five constants: the speed of light in vacuum, c; the Planck constant, h; the elementary charge, e; the Avogadro constant, NA; and the Boltzmann constant, kB, have known exact numerical values when expressed in SI units. The first three of these constants are fundamental constants, whereas NA and kB are of a technical nature only: they do not describe any property of the universe, but instead only give a proportionality factor for defining the units used with large numbers of atomic-scale entities.

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  1. S

    Are Cosmological & Universal Constants the Same?

    Are the cosmological constant and the universal constant essentially the same?
  2. ZenSerpent

    Single Phase Transformer Losses -- Hysteresis, Eddy Current Constants

    Hi. My colleagues and I are doing a research on transformers (single-phase) and we stumbled across the following equations involving hysteresis and eddy current losses: Wh = ηBmaxxfV where Wh = hysteresis losses η = Steinmetz hysteresis constant Bmax = maximum flux density x = constant...
  3. squelch

    Complex Numbers and Constants of Integration

    Homework Statement Suppose that the characteristic equation to a second order, linear, homogeneous differential equation with constant coefficients yielded two complex roots: \begin{array}{l} {\lambda _1} = a + bi\\ {\lambda _2} = a - bi \end{array} This would yield a general solution of: y =...
  4. F

    String theory and fundamental physical constants

    I have heard that ST can calculate the masses of the particles species of some vacuum and also its decay rate, charge and so on, but I have not seen any clear paper on the subject. Can anyone point me to one? Are "hbar" and "c" the same in all the vacuums?why or why not? Can ST predict the...
  5. S

    Deriving the structure constants of the SO(n) group

    The commutation relations for the ##\mathfrak{so(n)}## Lie algebra is:##([A_{ij},A_{mn}])_{st} = -i(A_{j[m}\delta_{n]i}-A_{i[m}\delta_{n]j})_{st}##.where the generators ##(A_{ab})_{st}## of the ##\mathfrak{so(n)}## Lie algebra are given by:##(A_{ab})_{st} =...
  6. M

    MHB Linear differential equations with constants coefficients

    Hey! :o Each element of the ring $\mathbb{C}[z, e^{\lambda z} \mid \lambda \in \mathbb{C}]$ is of the form $\displaystyle{\sum_{k=1}^n α_kz^{d_k}e^{β_kz}}$. A differential equation in this ring is of the form $$Ly = \sum_{k=0}^m \alpha_k y^{(k)}(z)=\sum_{l=1}^n C_lz^{d_l} e^{\beta_l z} , \ \...
  7. thegirl

    Cross product imaginary numbers

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  8. C

    Constants and variables (the very basics)

    Variable; A symbol for a number we don't know yet. It is usually a letter like x or y. Example: in x + 2 = 6, x is the variable. [mathsisfun.com] Q. Why is it called the variable? This seems to me to imply that its value varies. In the above example it seems to me to simply be the unknown...
  9. J

    Choosing Integrating constants for Electric Field

    Homework Statement A nonconducting disk of radius R has a uniform positive surface charge density sigma. Find the Electric field at a point along the axis of the disk at a distance x from its center. Assume that x is positive Homework Equations E=kq/r The Attempt at a Solution I know I'm...
  10. hideelo

    Expected rate of change, if at all, of nature's constants

    I am reading gravitation and spacetime by Hans Ohanian and he is discussing the possibility of the constants, such as proton mass, fine structure constant, etc, actually changing over time. He makes the claim that since the universe is ~10^10 years old the expected change should be...
  11. L

    First order differential equations and constants

    Homework Statement ##y' = \frac{cos x}{sin y}## ##y' = \frac{6x^2}{y(1 + x^3)}## Homework EquationsThe Attempt at a Solution So I was working through some textbook problems and there's something about the solutions of the above equations I don't quite understand. The first one: ##\int sin...
  12. manal gull

    How to calculate these coefficient constants....?

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  13. R

    How to Find Multiple Phase Constants

    Homework Statement A sinusoidal wave traveling in the –x direction (to the left) has an amplitude of 20.0 cm, a wavelength of 35.0 cm and a frequency of 12.0 Hz. The transverse position of an element of the medium at t = 0, x = 0 is y = –3.00 cm and the element has a positive velocity here. (a)...
  14. arpon

    Finding value of constants of quadric equation by experiment

    Homework Statement Suppose, the following equation describes the relation between an independent and a dependent variable physical quantities(that will be measured by experiments; for example, temperature, current, voltage etc) x & y : ##y = ax^2 + bx + c## We have to find the values of the...
  15. S

    How are proportionality constants in physical relations determined?

    I wanted to ask how are the values of proportionality constants in physical relations determined. How do we come to know their exact values ? An explanation with an example please...
  16. M

    Finding Unknown Constants for a Cubic Function with Given Derivatives

    Homework Statement determine the constants a,b,c, and d so that the function f(x)=ax^3+bx^2+cx+d has its first derivative equal to 4 at the point (1,0) and its second derivative equal to 5 at the point (2,4) Homework EquationsThe Attempt at a Solution I found the first and second derivative...
  17. jk22

    Proof that eigenvalues are constants

    i suppose matrices of the form $$A_i=\left(\begin{array}[cc] ccos(x_i)&sin(x_i)\\sin(x_i)&-cos(x_i)\end{array}\right)$$ And i consider the matrix $$C=A1\otimes A2\otimes 1_4-A1\otimes 1_4\otimes A2$$ I would like to show that the eigenvalues of C are independent of the x i tried with...
  18. N

    Difference Between Dimensional & Dimensionless Physical Constants

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  19. E

    Exploring the Quantum Eigenvalues of the 26 Basic Constants of Nature

    How many of the 26 basic constants of nature and more (beyond the standard model) where the values range can be said to be quantum eigenvalues and the exact constant being the *collapsed* one? In other words, Can you refer to the exact value as collapsed (quantum) one from the eigenvalues (or...
  20. A

    Kinetics question: calculating rate constants

    Homework Statement I need help for this kinetics question: Chlorination of butene at 0 degrees c, liquid phase, dichloromethane as solvent. initial concentration of butene is 0.1M conversion of 47.71% achieved after 3.1 hours. an additional 0.5M of hot butene was added at this point, which...
  21. rakeru

    Finding Constants to Solution Given 2nd Order, Nonlinear DE

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  22. L

    Which constants to use in Saha Equation

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  23. S

    Velocity/Acceleration relation w/ constants

    Homework Statement The velocity of a particle is related to its position by: v2 = w2 (A2 - x2) where w and A are constants. Show that the acceleration is given by: a=-w2x[/B]Homework EquationsThe Attempt at a Solution a= v* dv/dt v=(A2w2-x2w2)1/2 dv/dt= 1/2 (A2w2-x2w2)-1/2 * -2xw2 v *...
  24. F

    Understanding the Effective Spring Constant

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  25. Feodalherren

    Find the constants for given IVP

    Homework Statement Homework Equations DifEqs The Attempt at a Solution y ' = 4C1e-4xSinX - 4C2e-4xCosX y'(0) = -1 -1 = 0 - 4C2 Therefore C2 = 1/4 Not correct. What am I doing wrong?
  26. L

    Finding constants in exponential functions

    Homework Statement In 2000 the population of a country was estimated to be 8.23 million. In 2010 the population was 9.77 million. Assume that the number of people P(t) in millions at time t (in years since 2000) is modeled by the exponential growth function. P(t) = Aekt Find P(t) giving the...
  27. anemone

    MHB Finding Constants for Quadratic Equations

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  28. V

    Integration constants, gravitational potential of sphere

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  29. liometopum

    Constants linked to the observable universe, not whole

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  30. Lamdbaenergy

    What Happens If We Change Just One Physical Constant?

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  31. sheldonrocks97

    Find constants that satisfy integrals?

    Homework Statement ∫y1(x)^2dx from - to + infinity=1 and ∫y2(x)^2dx from - to + infinity=1 Homework Equations None that I know of. The Attempt at a Solution I evaluated the integrals and got that c1 is equal to c2 but I think that's wrong.
  32. T

    Finding constants for 3 wave functions

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  33. T

    How Do You Calculate the Force Constant of a Spring?

    I'm jut not sure how to solve this problem in general, I tried a couple ways, but I keep getting wrong answers and I only have 2 attempts left. Please give me a direction to go in! A spring is 17.1cm long when it is lying on a table. One end is then attached to a hook and the other end is...
  34. simplyphysics

    Spring Constants: Does Changing Diameter Affect Constant?

    Homework Statement If you change the diameter of a spring does it affect the spring constant? Assume the spring length, if fully extended, was kept constant. Homework Equations F=kx; F=mg The Attempt at a Solution From my research the spring constant (k) is measured by applying a mass and...
  35. P

    Exploring Equilibrium Constants & Kinetics: A Closer Look

    Consider the following generic equilibrium: aM + bN ⇌ cO + dP An equilibrium constant, K, can be defined as: $$K = \frac{[O]^c [P]^d}{[M]^a [N]^b}$$ But couldn't we also define another equilibrium constant similarly with coefficients that are in the same ratio as our original equation? For...
  36. M

    Understanding the Running of Mass in Particle Interactions

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  37. C

    Definite integral and constants

    Homework Statement If acceleration=dV/dt, V=def.integal from t1 to t2 of a*dt,=at+C. At t=0, C=V0. Why do we have a constant C, as a definite integral was calculated. Won't C2 and C1 cancel out? Homework Equations Definite integral from x1 to x2 of dx is x2-x1 without any constant, right? The...
  38. S

    How do I calculate van der Waals constants with 2 unknowns (a and b)?

    How would I go about calculating the units for the van der waals constants if I have 2 unknowns? (a and b) (P + a (n/V)^2) (V - n b) = n R T p=Pressure v=Volume n=moles R=gas constant T=temperature
  39. kmm

    C and h are not fundamental constants?

    I was looking through Zee's 'Quantum Field theory in a Nutshell" and he says that c and \hbar are "not so much fundamental constants as conversion factors." I've heard other physicists say this as well. I understand that these constants are used in some equations to give units of energy so...
  40. D

    Distribution of named and important mathematical constants

    I've noticed that the vast majority of named or important mathematical constants, are what you might call small numbers. Their modulus lies very often in the range [0,5]. Here's two examples of tables: http://en.wikipedia.org/wiki/Mathematical_constant#Table_of_selected_mathematical_constants...
  41. M

    Extreme Value Theorem true for constants?

    My textbook says the extreme value theorem is true for constants but I don't buy it. I mean I suppose that every value over a closed interval for a constant would be a maximum and a minimum technically but it seems like BS to me. Can anyone explain why this BS is true?
  42. S

    Are normalization constants of wave equation time dependent?

    The wave function solution psi is a function of time and position. Hence the integral of its square over all x will, in general, give a function of time. To normalize this, we must multiply with the inverse of the function. Therefore it seems that the normalization constant does not remain...
  43. M

    Faraday Effect: Calculating Vedet Constants

    Hi guys, so we currently ran an experiment where we calculated the verdet constant when laser light passed through a glass rod then through an analyzer to a photodetector. The experiment worked great for us but I wanted to know if anyone has ever calculated the verdet constant for any other...
  44. JasonHathaway

    Differential equations: Elimination of arbitrary constants

    Homework Statement Find the differential equation of ln y = ax^2 + bx + c by eliminating the arbitrary constants a, b and c. Homework Equations Wrosnkian determinant. The Attempt at a Solution I've solved a similar problem (y=ax^2+bx+c --> y'''=0), but couldn't do the same with...
  45. Math Amateur

    MHB If R is a domain , then units in R[x] are non-zero constants

    I am reading Joseph Rotman's book Advanced Modern Algebra. I need help with Problem 2.21 Part (i) on page 94. Problem 2.21 Part (i) reads as follows: -------------------------------------------------------------------- Let R be a domain. Prove that if a polynomial in R[x] is a unit, then it...
  46. FysixFox

    Concerning the Classical Electromagnetism and Gravitation Constants

    In classical electromagnetism, Coulomb's constant is derived from Gauss's law. The result is: ke = 1/4πε = μc^2/4π = 8987551787.3681764 N·m2/C2 Where ε is the electric permittivity of free space, μ is the magnetic permeability of free space, c is the speed of light in a vaccuum, and 4π is...
  47. Portal.Leaf

    Elimination of Arbitrary Constants (Differential Equations)

    Homework Statement Eliminate the arbitrary constants of the equation: ax2 + bx + cHomework Equations (Concept) According to my instructor, having n arbitrary constants makes an nth-order differential equation.The Attempt at a Solution I tried to differentiate 'til I get a third derivative so I...
  48. J

    Generator Constants: Understanding RLC Circuits in Series and Parallel

    If in a typical complete circuit (RLC) we have a resistor with resistence R, an inductor with inductance L and a capacitor with capacitance C, so the generator has which constants? And in second place, I was searching about the math of generators in series and parallel and I found something...
  49. FysixFox

    A quick question concerning constants and planck units

    Recently I have taken an interest in physical constants (and, through it, an interest in SI units and the upcoming redefinition of the kilogram). I actually have a list of almost all of them now, standard uncertainties included. After a bit, I decided to have a bit of fun messing around with the...
  50. N

    Understanding ∏ and other mathematical constants

    What exactly is ∏? I've never quite understood why it is apparent in so many different equations and formulas. Why is it there? Why is it apparent in nature so much? And ∏ it's just a infinite set of numbers why is it any more relevant than any other set of infinite numbers. Why is 3.14... so...
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