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Applet by Fu-Kwun
Hwang
Virtual Physics Laboratory |
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.
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Instructions on how to use the animation
below-
- The whole area has been divided into two region (Top/Buttom).
- Click within the black semi-circular near the top , then drag the
mouse (Left-Right) to change the angle of incidence.
- You can enter the ratio of index of refraction for those two media
(n2/n1).
- Click Faster/ Slower to change the wave speed.
- Suspend/Resume the animation.
- The animation is suspended when you
press down the left mouse button, it
is resumed when you released the mouse button.
- 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.
- 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.
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