What is Phase: Definition and 1000 Discussions

In the physical sciences, a phase is a region of space (a thermodynamic system), throughout which all physical properties of a material are essentially uniform. Examples of physical properties include density, index of refraction, magnetization and chemical composition. A simple description is that a phase is a region of material that is chemically uniform, physically distinct, and (often) mechanically separable. In a system consisting of ice and water in a glass jar, the ice cubes are one phase, the water is a second phase, and the humid air is a third phase over the ice and water. The glass of the jar is another separate phase. (See state of matter § Glass)
The term phase is sometimes used as a synonym for state of matter, but there can be several immiscible phases of the same state of matter. Also, the term phase is sometimes used to refer to a set of equilibrium states demarcated in terms of state variables such as pressure and temperature by a phase boundary on a phase diagram. Because phase boundaries relate to changes in the organization of matter, such as a change from liquid to solid or a more subtle change from one crystal structure to another, this latter usage is similar to the use of "phase" as a synonym for state of matter. However, the state of matter and phase diagram usages are not commensurate with the formal definition given above and the intended meaning must be determined in part from the context in which the term is used.

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  1. hello478

    Phase difference between two light waves of the same frequency

    the diagram. i found that the phase difference between them is 100º but how is the answer 260 can someone please explain?
  2. Skaiserollz89

    Relationship between Fourier coefficients and power spectral density

    Here, ##\Phi(f_{x_n},f_{y_m})=|\mathscr{F(\phi(x,y))}|^2 ## is the Power Spectral Density of ##\phi(x,y)## and ##\mathscr{F}## is the Fourier transform operator. Parseval's Theorem relates the phase ##\phi(x,y)## to the power spectral density ##\Phi(f_{x_n},f_{y_m})## by...
  3. George Wu

    A Relativistically invariant 2-body phase space integral

    I encounter a function that I don‘t know in the calculation of Relativistically invariant 2-body phase space integral: in this equation, ##s##is the square of total energy of the system in the center-of-mass frame(I think) I don't know what the function ##\lambda^{\frac{1}{2}}## is. There are...
  4. PhysicsTest

    Phase currents of Trapezoidal switching

    For trapezoidal switching or 180 degree switching these are the waveforms when i referred to the website 180 switching when i calculated the RMS value of the phase voltage it is Vp = 0.4714Vs so assuming the Vs = supply voltage = 20V and each phase - phase resistance as per the data sheet is...
  5. Leureka

    I Hidden phase in polarization tests of Bell's inequality?

    Hi there, i must preface with saying my understanding of the problem is limited to undergraduate quantum mechanics, since my spacialization is chemistry. I know the basic principles, like hilbert spaces, vector bases etc... I'm only asking this question because i genuinely want to understand...
  6. S

    I Topological phase transitions for the whole Universe...?

    Physicist Grigory Volovik has put forward some ideas about the universe undergoing a topological phase transition (especially in the early stages of the universe). He published a book called "*The Universe in a Helium Droplet*" where he explained his ideas. You can find a brief discussion here...
  7. Graffite

    I Two Waves In Phase: Exploring the Possibility w/ Graphs

    May I know how is it possible for two waves to be in phase when they have different amplitude? I couldn't find any existing graphs that clearly shows how the two waves are in phase, would anyone be able to sketch it out so I can have a look. Thank you:smile:
  8. Evari5te

    Three Phase Per Unit System - Mark up, represent as single phase equiv

    I'm seeking some reassurance I've understood the question since there are no answers given in the book and I'm getting a bit tied up in knots. What I am struggling with most is there are three per unit values for impedance already noted on the diagram without qualifying what ##Z{base}## is or...
  9. Q

    I Phase Contrast Telescope - Part II

    Over a year ago I started a post on a theoretical proposal for a phase contrast telescope (link here https://www.physicsforums.com/threads/why-no-phase-contrast-telescopes.1010127 ). However, the post was based on real experiences that were so different from anything I’ve ever experienced in my...
  10. L

    Rearrange formula and work out phase angle

    so far i think Ip = 10 f = 1000hz struggling with the phase angle
  11. H

    I Does an electron have a quantum phase frequency?

    Stationary solutions to the Schrödinger equation factor into a spatial part, e.g. atomic and molecular orbitals, and a temporal part that gives the phase rotation frequency. It is often assumed that adding a constant to the potential leaves the physics unchanged. And clearly, any "spectroscopic"...
  12. Philip551

    How can the direction of propagation help in determining the phase of a wave?

    Using the equation above I know that I have to find parameters k ##\omega## and ##\phi##. $$k = \frac{2\pi}{\lambda}$$ and $$\omega = 2\pi f$$ The problem I've been having is how you would go about finding ##\phi## since by solving: $$y(0,0)=0 \rightarrow sin(\phi)=0 \rightarrow \phi = 0...
  13. A

    B Phase Change in Light: A & B Signal Reflections

    I would appreciate knowing if there is any error in the mechanics illustrated in this animation with respect to phase change in the signal reflections shown at A and B, or in the description accompanying it. I have embedded the description with the animation and included it in this post for...
  14. simonjech

    I Lorentz invariant phase space and cross section

    Can someone please explain to me how can we obtain this integral in eq. 5.27 from eq. 5.26? I quite do not understand how is it possible to make this adjustment and why the (p_(f))^2 appeared there in the numerator and also why a solid angle appeared there suddenly.
  15. PhysicsTest

    Engineering Phase voltage and Line-Line voltage relation

    The below is the diagram i want to find the phase and line-line voltage relation I am finding difficulty in identifying the loop and applying the KVL. One attempt is U_{VA} - U_R - U_L -U_O - U_L - U_R = U_VB U_{VA} - 2(U_R+U_L) = U_VB -> eq1 Is my attempt correct? i am not confident please help.
  16. D

    A Heat exchange in a thermal storage based on phase change materials

    Hello, I want to model a thermal battery based on phase change materials (PCM). It is a plate heat exchanger immersed in a PCM bath. The diagram is given in the attached file. I want to determine the temperature at each moment and from everywhere in the battery. The hypotheses are the...
  17. L

    I Why do phase trajectories point upwards and downwards in a quadratic potential?

    Hi, I am currently preparing for my exam and have just watched a video about motion in phase space. From minute 4 a quadratic potential is introduced and then from minute 6 minute the phase trajectory. Here are the pictures quadratic potential phase trajectory Regarding phase...
  18. maxelcat

    Standing wave, phase and antiphase

    I think I understand that points P and R are pi radians out of phase - reaching their max/min at the same time. But are P and Q in anti phase? What is antiphase exactly - is it when they are 180deg out of phase - or is it when they are anything other than totally in phase? I seem to find...
  19. Manuel12

    Rectifier circuit for AC sources with 180˚ phase offset

    In a simple 2-phase generator that I am making, I have 2 pairs of oppositely placed copper coils in arrangement similar to this: I would like the generator to power DC devices. My question is: How could one rectify the output from opposing coils? Or, in other words, how could you rectify 2 AC...
  20. L

    A How to compute phase gradient from Snell's law?

    I am trying to figure out an intuitive understanding of how differential phase contrast (DPC) as a modality for measuring the phase shift as light passes through transparent samples. In a nutshell, DPC works by using either asymetric illumination or a split detector to standard compound...
  21. G

    Phase Transitions in the Van Der Waals Gas

    Hi, I am not quite sure if I have understood the second task correctly, but I proceeded as follows. It's about what happens to the isothermal compressibility when the free energy becomes minimal. In the first task there was already the equation ##\kappa_T=\frac{1}{V}\Bigl( \frac{\partial^2...
  22. G

    A Diffraction from a set of concentric rings with random phase

    I have been considering the properties of a Diffractive Optical Element (DOE) consisting of a very large number of concentric rings of equal (small) width, where the thicknessses of the rings are such as to produce random phase shifts in the range 0 to 2pi. I think I understand the behaviour of...
  23. Shreya

    Phase of a wave - My interpretation

    Let's begin my interpretation: (please refer the image below). There I have considered a point in the disturbance/wave (let's call it ##P##),(not a particle of the medium) and I follow it as the wave progresses. The solid curve is a Pic of the wave at ##t=0## and the dotted one is its Pic at...
  24. D

    A Energy hypersurface in a phase space (statistical physics)

    what is the reason for that the energy hypersurfaces in a phase space, which belong to systems with constant energy are closed? ( see picture )
  25. S

    B Phase Difference of Current & Voltage: Capacitors, Inductors & Complex Numbers

    how does capacitors and inductors cause phase difference between current and voltage? how does complex number come into play to explain the relation between phase of current and voltage?
  26. N

    I Exploring the Mysterious Acceleration Phase of Molecular Behaviour

    Princeton U. has a great intro to molec. behav. w. sound, but neither there or elsewhere have I found much on the initial acceleration phase. Is it assumed that movement over these nano-distances is already happening at c - and then there is just more of it ? How can a little stone you drop on a...
  27. person123

    Where can I find a PVT table for water for a 3-D webapp?

    I'm looking to create a little webapp where the user can see the 3-D PVT phase diagram, giving the user functionality like orbiting the surface and moving a point along the surface. (I attached an image of the surface I'm referring to). To do that, though, I would need the data defining the PVT...
  28. A

    Exploring 3 Phase Wire Amperage: Understanding Ampere Rules and Calculations

    If you have 3 phase power and let's say line A & B = 10 amperes line B & C = 10 amperes line C & A = 10 amperes For the single line B. Since it's in both in the first and second lines, then B can experience 10 + 10 = 20 Amperes? Or is it 15 A or still 10 Ampere? Thank you.
  29. W

    Electrical Turning a single phase motor into a generator

    Hi I’m a year 12 student and I’m trying to turn a washing machine motor into a generator. In my physics class we have only learned about AC generators using permanent magnets but the motor I’ve got doesn’t have any magnets and I believe that it is called an induction motor? Anyway I’m still...
  30. K

    What does the 'power' vs 'time' graph look like for a 3 phase AC supply?

    Hi, For years I wanted to understand why we have a 3 phase supply and not a 2 phase supply in AC. In Quora I found an interesting answer and was convinced about the purpose mentioned: Answer to Why there is no two phase electrical inputs instead of three phase and single phase? by Paul...
  31. Jamister

    A Measurement of the phase of coherent states

    It is commonly said that the phase of coherent states can't be measured, just the relative phase between two coherent states. A qubit example: define the states $$|\phi\rangle=[|0\rangle+\exp (\mathrm{i} \phi)|1\rangle] / \sqrt{2}$$ and the measurement operators...
  32. T

    I EM wave propagation: respective phase of E and M field

    Hi alltogether, I have been confused about a certain topic of EM wave propagation: it´s clear to me that E and M field are perpendicular to each other (I know Maxwell´s equations well). But: sometimes you can find on the internet that both fields are in phase...
  33. PhysicsTest

    Measuring Phase to Phase voltage using Multimeter

    I want to understand the concept of measuring the phase to phase voltage using multi meter. For example if i want to measure R-Y voltage, i connect the positive probe of the multi meter to the R phase and the negative probe to the Y phase. But both phases will be sinusoidal, so how does it...
  34. Philip Koeck

    I Phase velocity and frequency of a matter wave

    The relationships for matter waves are (see e.g. https://en.wikipedia.org/wiki/Matter_wave): λ = h / p and E = h f, where E = m c2 From this the phase velocity can be derived and we get vph = c2 / v. v is the group velocity, which is also the velocity of the particle. If I consider these...
  35. L

    Finding equilibrium temperature when there are phase changes

    If there weren't phase changes occurring I know that the temperature equilibrium would be ##T_e=\frac{m_{ice}c_{ice}T_{ice}+m_{w}c_{w}T_{w}}{m_{ice}c_{ice}+m_{w}c_{w}}##. Now, by repeating the reasoning to get the above formula (##\sum \Delta Q=0##) and adding the phase changes of the water...
  36. Callum Plunkett

    Engineering Half-power cut-off frequency and frequency and phase response.

    I have been given the attached following question: FIGURE 2 shows the response of a first-order filter to a step input. Estimate the half-power cut-off frequency of the filter and sketch its frequency and phase response. I believe that I have correctly calculated the half-power cut-off...
  37. runningphysics

    Incorrect Calculation of Time for Reactor Energy Phase Change

    I tried using the equation Q'*t= Q1+Q2. Where Q' is the energy of the reactor aka 200,000 kJ and t is the time. Take Q1 to be (1/2m*2257) and Q2 to be (1/2m*4.184*90). The 90 is the change in temperature for the phase change to occur from liquid water to gas, or boiling. Plugged everything in...
  38. K

    A How Does Quantum Theory Provide a Measure for Microstates in Phase Space?

    *Pathria, Statistical mechanics*"The microstate of a given classical system, at any time, may be defined by specifying the instantaneous positions and momenta of all the particles constituting the system. Thus. If ##N## is the number of particles in the system, the definition of a microstate...
  39. Dom Tesilbirth

    The magnetic phase change of an electromagnetic wave during reflection

    If the question had mentioned ##\overrightarrow{E}## instead of ##E_\bot##, then we could have used ##\overrightarrow{B}=\dfrac{1}{v}\widehat{k}\times \overrightarrow{E}## to get the direction of the magnetic field. But the question had only mentioned ##E_\bot##. To my understanding, knowing...
  40. Tertius

    A Local phase invariance of complex scalar field in curved spacetime

    I am stuck deriving the gauge field produced in curved spacetime for a complex scalar field. If the underlying spacetime changes, I would assume it would change the normal Lagrangian and the gauge field in the same way, so at first guess I would say the gauge field remains unchanged. If there...
  41. Dario56

    Extraction Flash Calculation - 4 Component and 2 Phase System

    I am performing extraction flash calculations for 4 component and 2 phase system. For anyone somewhat shaky with what extraction flash calculation is; extraction is performed, feed composition is known and we are calculating compositions of both phases at equilibrium, mole fraction of every...
  42. F

    What's the best shape function/element in finite element methods for phase field simulation?

    What's the best shape function/element in finite element methods for phase field simulation?
  43. casualguitar

    Modelling of two phase flow in packed bed (continued)

    Previous post linked here, where a model for the two phase flow of air through a packed bed was developed: https://www.physicsforums.com/threads/modelling-of-two-phase-flow-in-packed-bed-using-conservation-equations.1008754/ The first few comments on this new thread will be copies of the...
  44. S

    Convert 1 phase to 3 phase by using an old washing machine

    We were in the process of going off grid when a tree fell over our power line. Hence we got off grid before we were ready as we didn't want to repair the power line. Now everything in the house runs on solar power, except for the well pump. The problem with the well pump is that it is a 3 phase...
  45. H

    Engineering Decomposition minimal phase & all pass

    Hey everybody! I have put G1 = (1-s)/(2-10s) & G2 = (2-10s)/ (2 +10s) but than I read that all poles and zeroes should be inside the unit circle, and I don't know how to move the Zero S_01 = 1 to the unit circle
  46. binis

    A How is phase velocity related to deflection angle?

    Refractive index is a function of velocity in the medium. How is this related to deviation angle inside the medium? I am not asking for the known formula, but for the mechanism behind it.
  47. doggy

    How to wire a house using 3 phase

    We are getting 3 phase power delivered to our property via our own dedicated transformer. We want to rewire the house and other buildings so that we can use different appliances on different phases. We have 4 air conditioners, 3 hot water units and the usual assortment of things you would find...