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. A

    Dynamics of phase transitions

    I'm merely starting to research this field. Phase transitions have always been a mystery for me. Which kinds of dynamics govern when a material will undergo a phase transition? e.g., why is it exactly at the temperature T0 and pressure p0 that the substance X goes from one phase to the other...
  2. J

    Prandtl number of a g/l mixture (Ethane at phase transition)

    I have a problem in finding the heat transfer coefficient of a heat exchanger in which Ethane undergoes a phase transition. I would like to find the Prandtl number of Ethane in the phase transition region. So far I thought I would use the following: Pr_av = x * Pr_g + (1-x) Pr_l Pr_av =...
  3. D

    Finding attenuation, phase constant, and velocity

    Homework Statement Find the attenuation constant alpha, phase constant β, and phase velocity v if the conductivity of the material is σ=ωε the material parameters are μr=1, εr =2.5, and the wavelength in free space is λ naught = 30cm Homework Equations The Attempt at a Solution So...
  4. I

    Control torque of 3 phase motor

    Dear all, This is a newbie asking for some information. Actually, we have 1x30HP, 2x10HP motors working at our workplace. When we start the motors there is a lot of torque generated due to which our grid supply charges us penalty every month. We need information about the device(s) that...
  5. R

    Net Metering: Phase Matching for Solar Panels

    I was reading up on net metering, where the electric utility allows one to feed back excess generation by solar panels etc. onto the distribution network. http://en.wikipedia.org/wiki/Net_metering One question I had is, is it fairly easy to match phase for such inverters with the grid...
  6. E

    Phase Shift of Reflected Wave in Conductive Material

    Homework Statement An EM wave normally shed on a conductive material (\tilde{\epsilon}=\epsilon+i\epsilon_i,\mu_0). Calculate the phase shift of the electric field of the reflected wave relative to that of the incident wave. Homework Equations...
  7. N

    Electric field Phase change upon rarer to denser reflection of an EM

    Can anyone please provide an intuitive explanation of why phase shift of 180 degrees occurs in the Electric Field of a EM wave,when reflected from an optically denser medium and also why the phase remains same on reflection from a denser to rarer medium? please try to explain on an atomic/sub...
  8. S

    Qualitative advice on two phase flow problem.

    Hi guys I have a rather qualitative question. let's imagine a tank with two openings. pressure is measured at one opening (A) to be at a constant 33 bar at time t=0s. the other opening(B) is at atmospheric pressure. Inside the tank we have a two phase flow half is N2 gas and the other half is...
  9. L

    Do spin-1 particles also have phase symmetry?

    In almost every QFT or particle textbook we learn that complex scalar fields or spinor fields (or even multiplets of spinor fields) have a phase symmetry (global gauge symmetry.) You can append to these fields an exponential with a complex phase in the Lagrangian and the dynamics remain the...
  10. J

    Is there a phase shift associated with twisted nematic LCDs?

    Hello, As it says in the title, I would like to know if the light entering a twisted nematic liquid crystal display experiences any kind of phase shift specifically when applying a voltage to manipulate the polarisation of the light. If it is the case, could someone point me towards any...
  11. J

    Digital Image Processing, Phase offset

    Homework Statement I'm working on a Matlab problem for a digital image processing class. The problem is to take an image, then take its 2D-FFT and offset the phase component by pi. Then to take the IFFT of the new DFT using the unmodified magnitude and modified phase. What I got was a...
  12. S

    Why is Phase Velocity Greater than Speed of Light?

    why is the phase velocity(c^2/v) greater than c?? since v<c it should be greater than c.. how does this happen?
  13. A

    Line Current in a 2 phase transformer

    I am a graduate engineer and have been set a small task to work out the current (primary side) in a 2 phase 30kVA 415:650 transformer. The 2 phases have been utilized from a 3 phase source and are hence 120 degrees out of phase. I understand had it been a 3 phase 30kVA transformer I could...
  14. A

    Understanding Refractive Phase Differences in Electromagnetic Waves

    I'm wondering about small changes of phase due to a refractive medium. For example, suppose there is an emitter of radio or light waves, and two detectors equidistant from the emitter. One of the detectors is behind a medium, while the other is a straight shot through a vacuum. How would...
  15. S

    Travel through different vacuum phase

    It could be possible for a driven vacuum bubble (like an Alcubierre drive,assuming that it could be possible to realize ) to travel not only many order of magnitude faster than light but even trough different vacuum phase ? like for example region of false vacuum ?
  16. R

    Medium Voltage Motors Phase Rotation Test

    Is it possible to check the phase rotation sequence of a Medium Voltage Motor (Up to 6 kV) with one instrument? Does the shaft need to be moving while it is being tested? If instead of one, there are two motors electrically connected in parallel, with a common source feeder. will it be...
  17. B

    Why do some P,T sets of data give wrong readings in phase transition problems?

    Homework Statement http://icho2013.chem.msu.ru/materials/IChO-2013_Theoretical_Official_English_Version.pdf Looking at problem 1. Homework Equations The integrated form of the Clausius-Clapeyron equation: ln(\frac{P_{T2}}{P_{T1}}) = -\frac{\Delta H}{R} \cdot (\frac{1}{T_2} -...
  18. F

    But, as a webpage title: Wave Problem: Solving for Phase Shift

    Homework Statement 1. A signal of the form x(t) = A cos(ω0t + φ) is plotted below. From the plot, deduce the following: (a) the amplitude A, (b) the period T0, (c) the radian frequency ω0, and (d) the phase φ in radians. For part (e), find f0 in Hz by converting the radian frequency from part...
  19. Pythagorean

    Phase I of clinical HIV vaccine trial successful

    note: Phase I is just safety testing, not efficacy. Still exciting, though! http://communications.uwo.ca/media/releases/2013/September/no_adverse_effects_in_volunteers_following_phase_i_clinical_trial_of_sumagen_aids_vaccine.html
  20. C

    Single phase 415volt loads

    When a single phase 415 / 480 volt load is connected, one Kw/h meter will turn in the right direction whilst the other will turn in the reverse direction. This is the case whether the load is a welder or flood light or inductive heater. Can anybody please explain the reason why?
  21. J

    Three Phase PV Grid-Tied System(MPPT)

    Homework Statement Currently, I'm doing on a research of this three phase PV grid tied system. I found a model and try to run and simulate for further understanding. There's an attachment of a model three phase pv grid tied system in Simulink. However, I've a hard time understanding the MPPT...
  22. A

    Half-silvered rear surface phase shift

    I have read that the rear surface reflection of a half-silvered mirror undergoes no phase shift. But they caution that this is true only for a dielectric mirror. What is the answer for a metallized mirror? It seems to me that the answer must either be 180 degr., or pass continuously to 180 degr...
  23. N

    Pseudo frequency? Related to phase shift

    I am reading a text about how MRI works and I came across a thing that I am totally confused. The book mentions about that few particles side by side with their nuclei spinning at the same frequency but they all have a phase difference. Since MRI cannot measure the phase differences directly...
  24. H

    MATLAB Cavity simulation on matlab with spatially dependent phase

    Hello there, I have been searching for MATLAB simulations that analyze optical cavities and there are some useful codes. Yet, I haven't found codes that analyze what happens to cavit transverse modes if spatially dependent phase is introduced between mirrors Does anybody know if there...
  25. C

    Simple phase relationship (current & voltage)

    Homework Statement Given tthe following voltage and current i(t) = 5sin(377t - 20°)A v(t) = 10cost(377t + 30°)V Determine phase relationship between i(t) and v(t) Homework Equations wave functions wave properties The Attempt at a Solution Would the phase relationship simply be 50°...
  26. M

    Phase Synchronisation Techniques

    Hello Everyone, I was wondering if anyone out there would know any kind of phase synchronisation techniques used in mobile/satellite communication. Thanks in advance With Regards, Max
  27. O

    Calculating gain of a phase detector

    I have a linear model of a phase detector (phase lock loop) represented by the block diagram below. It is designed to maintain zero difference in phase between the input carrier signal and a local voltage controlled oscillator. Phase demand→Ka→F(s)→K/s→Phase output F(s) =...
  28. B

    Expressing Rates of S's Phase Transition: P1, T1, and Activity of S (Phase 1)

    Let's say I have a general phase transition S (phase 1) ::equil:: S (phase 2). At a certain point in pressure and temperature for each phase (they can have different pressures and temperatures, we might say P1 and T1 for phase 1 and P2 and T2 for phase 2), how might we express the forward and...
  29. R

    An intuitive meaning to the phase constant k?

    k being the one from the harmonic wave ψ(x,t) = Asin(kx - ωt) where k = 2π/λ The way I see it right now, k is just defined this way to get the period of sin(x) to be λ by using sin(kx), so I wondered if there's something more to it. (Though I know it can be used as an vector to declare the...
  30. T

    Three phase delta transformers

    Dumb question - if the phases are tied together in a three phase delta transformer why don't the phases short out against each other in the same way the transmission lines would fault phase to phase if the touched each other in the overhead? I think I understand the wye winding situation in...
  31. M

    Operating principle of a Six Phase induction motor

    Hi Sir, I have seen in many IEEE magazines that, a six phase induction motor is having two 3 phase windings spatially separated by an angle of 30 degrees electrical. I have attached the 6 phase induction motor diagram. But I am not able to understand how the motor operates i.e. how the rotor...
  32. K

    Representation of a 1 phase transmission line as line charges

    Hi, According to what I understood, when a terminal is connected to a line, it causes electrons to flow in one direction. And so for a single phase transmission line in parallel if connected to supply, then in one side electrons will be flowing in one direction and the same electrons will be...
  33. T

    Ionization driven phase change

    Greetings, I've been searching online without success for information related to the process (name?) Of utilizing the repusive force between negatively ionized particles to facilitate a change of phase from liquid to plasma. I would like to be able to take a substance in liquid form inside a...
  34. J

    Cherenkov radiation - phase velocity not group velocity

    Why must the charged particle that leads to Cherenkov radiation travel faster than the phase velocity of light not the group velocity of light? One of the sides of the triangle that is used to define cosθ is v=c/n i.e. the phase velocity. I don't see why it's one rather than the other. Thanks!
  35. M

    Problems with currents and phase

    I am still trying to solve this but I first, I need someone to explain to me about the sum of the currents, which I don't understand. The phasor of current I1 is 2+3j[A], and the phasor of current I2 is 1[A]. 1) Find the value of impedance Z. 2) Let the phase difference (arg(I3/I4)) between...
  36. O

    Current phase between inductor and capacitor in LCR-circuit

    At resonance (## \omega_0^2= 1/LC##) in an LCR-Circuit the phase angle given by \theta=\tan^{-1}\left( \frac{\omega L - 1/\omega C}{R} \right) obviously is zero. And still there are other phases to deal with. This I don't understand. Let me elaborate. For example when calculating the amount...
  37. F

    Where does the Berry phase of $\pi$ come from in a topological insulat

    The Berry connection and the Berry phase should be related. Now for a topological insulator (TI) (or to be more precise, for a quantum spin hall state, but I think the Chern parities are calculated in the same fashion for a 3D TI). I can follow the argument up to defining the Chern parity $\nu$...
  38. D

    Phase retrieval problem for laser profile

    Good morning, Before all, I also posted a question to maths forum, but I am convienced that this is the forum I was more like looking for. Firstly, hello to this forum, secondly I want to apologize if this is not a place I would like to post a question like that, maybe in another thread ?; )...
  39. hilbert2

    One-particle system with phase transition?

    Hi, I'm Teemu from Finland, and I'm just getting my master's degree in physics completed (only one course in electronics left). This is my first post in Physicsforums. I was thinking about a problem in statistical mechanics. As you all know, if we have a one- particle system where the...
  40. C

    Including a heat for a phase change or not?

    Hi PF! I just took a test for my class and there is one problem I can't get my mind off of. I'm not necessarily looking for the correct solution here, just if my thinking was correct. It went more or less like this: there is 40g of ice at 0 degrees C in 200g of water in an aluminum calorimeter...
  41. B

    Pressure on (T,P) Phase Diagram for Substance

    On a (T,P) phase diagram, what is meant by the pressure at each phase for the substance? Chemically speaking we are only usually dealing with "gaseous" pressure (i.e. that exerted by the gases), but only when the substance is in (one of the phases in) the gaseous state or supercritical fluid...
  42. M

    Phase change in lock-in amplifier

    I just started to use a lock-in amplifier, and I am trying to following the procedures by adjusting zero phase. But my input phase changes with time and sensitivity, and I couldn't lock in onto it. The question is, is this normal that phase changes all the time during the experiment or if there...
  43. Y

    What is scalar voltage potential with phase shift means?

    Say ##V_{out}=4e^{j\frac {\pi}{6}}##, what is this mean? It is a scalar voltage. Does this means: 4e^{j\frac {\pi}{6}}=4\left(\cos \frac {\pi}{6}+j\sin \frac {\pi}{6}\right) = 4(0.866+j0.5) = 3.4641+j2=4\angle 30^o What is the phase shift means, reference to input? Thanks
  44. D

    Putting phase factor in amplitude in Lorentz oscillator

    Hi there, In my course solid state physics, there is a part about the Lorentz oscillator. At a certain part, this is written: "X(t) = X_0sin(-ωt+α) This changes into: X(t) = X_0 exp(-iωt) by choosing X_0 as a complex number and putting the phase factor into the complex amplitude."...
  45. A

    Group velocity and phase velocity of a matter wave

    Hi. Today I sat my final first year Modern Physics exam. It went very well, however I got stuck in one question. It asked (i) to prove the following relation for the matter wave \omega^{2}=k^{2}c^{2}+m^{2}c^{4}/\hbar^{2} and (ii) to obtain the group velocity and phase velocity of a matter wave...
  46. B

    What is the relationship between equilibrium constant and phase diagrams?

    On a phase diagram, the lines are "lines of equilibrium", i.e. at any point on these lines of equilibrium there is an established equilibrium between the two phases on either side of the line. The equilibrium constant is a function of temperature and pressure, and the various other thermodynamic...
  47. sunrah

    Relationship between trace and phase space

    So I noticed we can define entropy in two very different ways: 1) quantum mechanically S = -k Tr(\hat{\rho}\ln{(\hat{\rho})}) 2) classically S = -k \int \rho \ln{(\rho)} d\Gamma where Tr is the trace and d\Gamma = \frac{1}{h^{3N}N!}\prod_{i}^{N} d^{3N}q_{i}d^{3N}p_{i} is the phase...
  48. B

    Lamp color before and after a phase of acceleration

    You have a yellow lamp in your spaceship. Now you accelerate your spaceship significantly. Then you stop accelerating. Does the lamp still have the same color? I would think it should, but I reckon differently as follows: Consider the situation from an outside observers point of view, resting...
  49. fluidistic

    Confused on phase diagrams for binary systems (thermodynamics)

    I'm confused regarding the phase diagrams of binary systems. Let's suppose we mix 2 liquids, A and B at a given pressure P that won't change during the whole experiment. I raise the temperature until I observe that some of the mix of liquids vaporizes. What boggles me is that it seems I can...
  50. Z

    MHB Stability, phase portrait, bifurcations

    I am stuck with another one -- Assume that f(x) has the following graph: (for graph please see the attachment) Consider the (1-dimensional) ODE: X’ = f(x): (a) Find all the xed points, and study their stability. (b) Draw the phase portrait of the system, as well as the graphs of the...
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