The Transmission of Wave through Dense media -- Reflection and Refraction



The Huygens–Fresnel principle:It recognizes that each point of an advancing wave front is in fact the center of a fresh disturbance and the source of a new train of waves; and that the advancing wave as a whole may be regarded as the sum of all the secondary waves arising from points in the medium already traversed.
[img]http://www.phy.ntnu.edu.tw/ntnujava/index.php?action=dlattach;topic=16.0;attach=1078;image[/img]


How to play:


  1. The whole area has been divided into two region (Top/Buttom).

  1. Click within the black semi-circular near the top , then drag the mouse (Left-Right) to change the angle of incidence.

  2. You can enter the ratio of index of refraction for those two media (n2/n1).

  3. Click Faster/ Slower to change the wave speed.

  4. Suspend/Resume the animation.


    1. The animation is suspended when you press down the left mouse button, it is resumed when you released the mouse button.

    2. If you press the right mouse button, the animation is also suspended. But you will have to press the right mouse button again to resume the animation.

    3. What if I press the right mouse button first then press the left mouse button ? Try it!


* For sound wave originates in and impings on water:

If the incident angle is larger than critical angle (about 13 degree),

the sound wave will be total reflected. No sound will be transmitted.



When a beam of light impings at some angle on the smooth flat surface of an optically dense medium, the wave "sees" a vast array of very closely spaced atoms that will somehow scatter it.
(At the wavelengths of light -- d=500nm -- the Earch's atmosphere at STP has about 106 molecules in such a d3-cube).
As the wavefront descends, it excites one scatterer after another, each of which reradiates a stream of photons that can be thought of as a hemispherical wavelet in the incident medium.
Because the wavelength is so much greater than the separation between the molecules, the wavelets advance together and add constructively in only one directions, and there is one well-defined reflected beam.
The wavelets bend as they cross the boundary, because of the speed change.
For similar reason, they form one well-defined refracted beam.





Ratio of index of refraction n2/n1 = v1/v2, where v1, v2 are speed of wave in media 1 and 2.
For light (electromagnetic wave):


substancesAirWaterPlexglassDiamond
indices of refraction1.000291.3331.512.417

For sound wave :


materialAirwater vaporfresh watersea waterAluminum
speed of sound (m/s)331401149315135104



http://www.youtube.com/watch?v=xwzw5GhpC_0