Applet by Fu-Kwun Hwang

    Virtual Physics Laboratory

    Large Simulation

    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.

    Instructions on how to use the animation below-
    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.