phase

(noun)

Waves are said to be "in phase" when they begin at the same part (e.g., crest) of their respective cycles.

Related Terms

Examples of phase in the following topics:

  • The Evaporating Atmosphere

    • Within each phase, the properties are uniform but between the two phases properties differ.
    • Water in a closed jar with an air space over it forms a two phase system.
    • Even at equilibrium, molecules are constantly in motion and, once in a while, a molecule in the liquid phase gains enough kinetic energy to break away from the liquid phase and enter the gas phase.
    • The water vapor in it changes phases.
    • It is in a phase equilibrium.

  • Phase Changes and Energy Conservation

    • A phase of a thermodynamic system and the states of matter have uniform physical properties.
    • The measurement of the external conditions at which the transformation occurs is termed the phase transition.
    • There are well-defined regions on these graphs that correspond to various phases of matter, so PT graphs are called phase diagrams .
    • Using the graph, if you know the pressure and temperature you can determine the phase of water.
    • The solid lines—boundaries between phases—indicate temperatures and pressures at which the phases coexist (that is, they exist together in ratios, depending on pressure and temperature).

  • Latent Heat

    • The latent heat is the energy associated with a phase change of a substance.
    • There is no temperature change until a phase change is complete.
    • Significant amounts of energy are involved in phase changes.
    • This example shows that the energy for a phase change is enormous compared to energy associated with temperature changes without a phase change.
    • There is no temperature change until a phase change is complete.

  • Conditions for Wave Interference: Reflection due to Phase Change

    • This is constructive interference and occurs when the phase difference between the waves is a multiple of 2π.
    • Assuming the two waves are in phase at point B, then the relative phase changes along the x-axis.
    • The phase difference at point A is given by:
    • Destructive interference occurs when the waves are half a cycle out of phase, or
    • In other words, the wave undergoes a 180 degree change of phase upon reflection, and the reflected ray "jumps" ahead by half a wavelength.

  • Spherical and Plane Waves

    • Spherical waves come from point source in a spherical pattern; plane waves are infinite parallel planes normal to the phase velocity vector.
    • Constructive interference occurs when waves are completely in phase with each other and amplifies the waves.
    • Destructive interference occurs when waves are exactly out of phase with either other, and if waves are perfectly out of phase with each other, the wave will be canceled out completely.
    • A plane wave is a constant-frequency wave whose wavefronts (surfaces of constant phase) are infinite parallel planes of constant peak-to-peak amplitude normal to the phase velocity vector .

  • Wavelength, Freqency in Relation to Speed

    • They also have two kinds of velocity: phase and group velocity.
    • where v is called the wave speed, or more commonly,the phase velocity, the rate at which the phase of the wave propagates in space.
    • This is the velocity at which the phase of any one frequency component of the wave travels.
    • For such a component, any given phase of the wave (for example, the crest) will appear to travel at the phase velocity.
    • (The group velocity is positive and the phase velocity is negative. )

  • Phase Angle and Power Factor

    • In a series RC circuit connected to an AC voltage source, voltage and current maintain a phase difference.
    • Therefore we can say: the currents in the resistor and capacitor are equal and in phase.
    • we notice that voltage $v(t)$ and current $i(t)$ has a phase difference of $\phi$.
    • Because voltage and current are out of phase, power dissipated by the circuit is not equal to: (peak voltage) times (peak current).
    • The fact that source voltage and current are out of phase affects the power delivered to the circuit.

  • Power

    • Here, $\phi$ is called the phase angle.
    • As seen in previous Atoms, voltage and current are out of phase in an RLC circuit.
    • There is a phase angle ϕ between the source voltage V and the current I, given as
    • This implies that ϕ=0º and that voltage and current are in phase, as expected for resistors.
    • \phi is the phase angle, equal to the phase difference between the voltage and current.

  • Phase-Space Density

    • The phase-space density of particles gives the number of particles in an infinitesimal region of phase space,
    • If there is no dissipation, the phase-space density along the trajectory of a particular particle is given by

  • Young's Double Slit Experiment

    • (This means that the light sources were in the same phase. ) The two slits cause the two coherent light sources to interfere with each other either constructively or destructively.
    • Destructive wave interference occurs when waves interfere with each other crest-to-trough (peak-to-valley) and are exactly out of phase with each other.
    • The waves all start out in phase (matching crest-to-crest), but depending on the distance of the point on the wall from the slit, they could be in phase at that point and interfere constructively, or they could end up out of phase and interfere with each other destructively.
    • (a) Pure constructive interference is obtained when identical waves are in phase.
    • (b) Pure destructive interference occurs when identical waves are exactly out of phase (shifted by half a wavelength).