Question

why is the phase change in going rare to denser

Answer 1

Phase change occurs at transition of a wave from one medium to another because of change in the velocity of propagation of the wave. Intensity changes are due to some reflection at the interface as well as attenuation due to scattering of energy of the wave by the particles of the medium. In a denser medium there would more particles and hence greater scattering.The relationship between period, frequency, and amplitude for a sine wave is illustrated in this image[1]
Phase is the position of a point in time (an instant) on a waveform cycle. A complete cycle is defined as the interval required for the waveform to return to its arbitrary initial value. The graph to the right shows how one cycle constitutes 360° of phase. The graph also shows how phase is sometimes expressed in radians, where one radian of phase equals approximately 57.3°.'

Phase can also be an expression of relative displacement between two corresponding features (for example, peaks or zero crossings) of two waveforms having the same frequency.[1]

In sinusoidal functions or in waves, "phase" has two different, but closely related, meanings. One is the initial angle of a sinusoidal function at its origin and is sometimes called phase offset or phase difference. Another usage is the fraction of the wave cycle that has elapsed relative to the origin.[2]

Phase shift Edit


Illustration of phase shift. The horizontal axis represents an angle (phase) that is increasing with time.
Phase shift is any change that occurs in the phase of one quantity, or in the phase difference between two or more quantities.[2]

This symbol: {\displaystyle \varphi \,} is sometimes referred to as a phase shift or phase offset because it represents a "shift" from zero phase.

For infinitely long sinusoids, a change in {\displaystyle \varphi \,} is the same as a shift in time, such as a time delay. If {\displaystyle \scriptstyle x(t)\,} is delayed (time-shifted) by {\displaystyle \scriptstyle {\frac {1}{4}}\,} of its cycle, it becomes:

{\displaystyle {\begin{aligned}x\left(t-{\tfrac {1}{4}}T\right)&=A\cdot \cos \left(2\pi f\left(t-{\tfrac {1}{4}}T\right)+\varphi \right)\\&=A\cdot \cos \left(2\pi ft-{\tfrac {\pi }{2}}+\varphi \right)\end{aligned}}}
whose "phase" is now {\displaystyle \scriptstyle \varphi \,-\,{\frac {\pi }{2}}}. It has been shifted by {\displaystyle \scriptstyle {\frac {\pi }{2}}} radians (the variable {\displaystyle A} here just represents the amplitude of the wave).

Phase difference

Formula for phase of an oscillation or a wave

See also

References

External links